U.S. patent application number 16/315739 was filed with the patent office on 2020-07-30 for aluminum alloy rolled material for molding, with improved press formability, bending workability, and ridging resistance.
The applicant listed for this patent is UACJ CORPORATION. Invention is credited to Yuya SAWA, Yusuke YAMAMOTO.
Application Number | 20200239991 16/315739 |
Document ID | 20200239991 / US20200239991 |
Family ID | 1000004767477 |
Filed Date | 2020-07-30 |
Patent Application | download [pdf] |
United States Patent
Application |
20200239991 |
Kind Code |
A1 |
YAMAMOTO; Yusuke ; et
al. |
July 30, 2020 |
ALUMINUM ALLOY ROLLED MATERIAL FOR MOLDING, WITH IMPROVED PRESS
FORMABILITY, BENDING WORKABILITY, AND RIDGING RESISTANCE
Abstract
The present disclosure provides an aluminum alloy rolled
material for molding, including an Al--Mg--Si--Cu-based alloy
containing 0.30 mass % or more Cu. A ratio of a cube orientation
density to a random orientation is 10 or more in a plane that is
perpendicular to a sheet thickness direction and is at a depth of
1/4 of a total sheet thickness from a surface. An absolute value of
a difference between a maximum value and a minimum value of an
average Taylor factor in a case in which molding is assumed to
cause plane strain deformation having a main strain direction that
is a rolling width direction is 1.0 or less. The average Taylor
factor is obtained for each of subareas that are obtained by equal
division of an area, having a 10 mm width in the rolling width
direction and a 2 mm length in a rolling direction, into 10
subareas in the rolling width direction. The subareas are in a
plane that is perpendicular to the sheet thickness direction and is
at a depth of 1/2 of the total sheet thickness from the
surface.
Inventors: |
YAMAMOTO; Yusuke; (Tokyo,
JP) ; SAWA; Yuya; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UACJ CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
1000004767477 |
Appl. No.: |
16/315739 |
Filed: |
July 13, 2017 |
PCT Filed: |
July 13, 2017 |
PCT NO: |
PCT/JP2017/025582 |
371 Date: |
January 7, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/057 20130101;
C22F 1/05 20130101; C22C 21/16 20130101; C22C 21/18 20130101; C22C
21/14 20130101; B21B 2003/001 20130101; B21B 3/00 20130101 |
International
Class: |
C22F 1/057 20060101
C22F001/057; C22C 21/18 20060101 C22C021/18; C22C 21/16 20060101
C22C021/16; C22C 21/14 20060101 C22C021/14; C22F 1/05 20060101
C22F001/05; B21B 3/00 20060101 B21B003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 14, 2016 |
JP |
2016-139812 |
Feb 14, 2017 |
JP |
2017-025445 |
Claims
1. An aluminum alloy rolled material for molding, with improved
press formability, bending workability, and ridging resistance, the
aluminum alloy rolled material comprising: an aluminum alloy
comprising 0.30 to 1.50 mass % Cu, 0.30 to 1.50 mass % Si, 0.30 to
1.50 mass % Mg, at least one of 0.50 mass % or less Mn, 0.40 mass %
or less Cr, or 0.40 mass % or less Fe, and a balance of Al and
inevitable impurities, wherein a difference between a tensile
strength and a 0.2% proof stress is 120 MPa or more, wherein a
ratio of a cube orientation density to a random orientation is 10
or more in a plane that is perpendicular to a sheet thickness
direction and is at a depth of 1/4 of a total sheet thickness from
a surface, and wherein an absolute value of a difference between a
maximum value and a minimum value of an average Taylor factor in a
case in which molding is assumed to cause plane strain deformation
having a main strain direction that is a rolling width direction is
1.0 or less, the average Taylor factor being obtained for each of
subareas that are obtained by equal division of an area, having a
10 mm width in the rolling width direction and a 2 mm length in a
rolling direction, into 10 subareas in the rolling width direction,
the subareas being in a plane that is perpendicular to the sheet
thickness direction and is at a depth of 1/2 of the total sheet
thickness from the surface.
2. The aluminum alloy rolled material for molding according to
claim 1, wherein the aluminum alloy contains at least one of 0.03
to 0.50 mass % Mn, 0.01 to 0.40 mass % Cr, or 0.03 to 0.40 mass %
Fe.
3. The aluminum alloy rolled material for molding according to
claim 2, wherein the aluminum alloy contains at least one of 0.03
to 0.15 mass % Mn, 0.01 to 0.04 mass % Cr, or 0.03 to 0.40 mass %
Fe.
4. The aluminum alloy rolled material for molding according to
claim 1, wherein the aluminum alloy contains 0.03 to 0.80 mass %
Cu.
5. The aluminum alloy rolled material for molding according to
claim 1, wherein the aluminum alloy contains 0.03 to 0.80 mass %
Mg.
6. The aluminum alloy rolled material for molding according to
claim 1, wherein the difference between the tensile strength and
the 0.2% proof stress is 121 to 133 MPa.
7. The aluminum alloy rolled material for molding according to
claim 1, wherein the ratio of the cube orientation density to the
random orientation is 12 or more.
8. The aluminum alloy rolled material for molding according to
claim 7, wherein the ratio of the cube orientation density to the
random orientation is 12 to 18.
9. The aluminum alloy rolled material for molding according to
claim 1, wherein the absolute value of the difference between the
maximum value and the minimum value of the average Taylor factor is
0.9 or less.
10. The aluminum alloy rolled material for molding according to
claim 9, wherein the absolute value of the difference between the
maximum value and the minimum value of the average Taylor factor is
0.5 to 0.9.
11. The aluminum alloy rolled material for molding according to
claim 1, wherein, in 180-degree bending working, a score given by
comparison with workability evaluation samples is 6 or more.
12. The aluminum alloy rolled material for molding according to
claim 11, wherein, in the 180-degree bending working, the score
given by comparison with the workability evaluation samples is 7 or
more.
13. The aluminum alloy rolled material for molding according to
claim 12, wherein, in the 180-degree bending working, a score given
by comparison with the workability evaluation samples is 8 or
more.
14. The aluminum alloy rolled material for molding according to
claim 1, wherein the aluminum alloy rolled material is obtained by
rolling working including hot rolling working, and an average
particle size of precipitated particles having particle diameters
of 0.4 to 4.0 .mu.m is 0.6 .mu.m or more in pre-rolling heating and
retention prior to the hot rolling working.
15. The aluminum alloy rolled material for molding according to
claim 14, wherein the average particle size of the precipitated
particles having particle diameters of 0.4 to 4.0 .mu.m is 0.7 to
1.9 .mu.m.
16. The aluminum alloy rolled material for molding according to
claim 14, wherein a density of the precipitated particles having
particle diameters of 0.4 to 4.0 .mu.m is equal to or less than
1500 particles/100 .mu.m.sup.2.
17. The aluminum alloy rolled material for molding according to
claim 16, wherein the density of the precipitated particles having
particle diameters of 0.4 to 4.0 .mu.m is 402 particles/100
.mu.m.sup.2 to 1411 particles/100 .mu.m.sup.2.
18. The aluminum alloy rolled material for molding according to
claim 1, wherein a recrystallization rate after the hot rolling
working is 95% or more.
19. The aluminum alloy rolled material for molding according to
claim 18, wherein the recrystallization rate after the hot rolling
working is 100%.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to an Al--Mg--Si--Cu-based
aluminum alloy rolled material which is subjected to molding and
coating baking and is used as the members and components of various
automobiles, ships, aircraft, and the like, such as automobile body
sheets and body panels, construction materials, structural
materials, and other materials for various machinery and
appliances, household electrical appliances, the components
thereof, and the like. In particular, the present disclosure
relates to an aluminum alloy rolled material for molding, with
improved press formability, bending workability, and ridging
resistance, which is preferred for the applications.
BACKGROUND ART
[0002] Demands for improvement in fuel efficiency through a
reduction in the weights of automobiles have been increased against
recent requirements such as suppression of global warming and a
reduction in energy costs as backgrounds. In response to the
demands, aluminum alloy sheets have also increasingly tended to be
used as automotive body sheets applied to automobile body panels,
in place of conventional cold rolled steel sheets. An aluminum
alloy sheet has a specific gravity about one-third the specific
gravity of a conventional cold rolled steel sheet while having a
strength approximately equivalent to the strength of the
conventional cold rolled steel sheet, and can contribute to a
reduction in the weight of an automobile. Aluminum alloy sheets
have also been recently often used in molded components such as the
panels and chassis of electronic and electrical instruments and the
like, in addition to automotive applications. Like automotive body
sheets, such aluminum alloy sheets have been often pressed and
used.
[0003] The press formability of the sheet materials for molding has
been more strictly required because the design properties of the
shapes of automobiles and the like have been highly required in
recent years. The automotive body panels have been often used after
hemming of the edges of sheets in order to join and integrate outer
and inner panels. The hemming can be considered to be very severe
working for a material because 180-degree bending is performed at
an extremely small bend radius. Thus, improved hemming workability
and improved bending workability in consideration of such
applications are required. In addition, automobile body sheets have
been usually used after subjected to coating baking. In a balance
between formability and strength, therefore, it is necessary to
obtain high strength after the coating baking in the case of
attaching great importance to the strength, whereas it is necessary
to obtain high press formability at the expense of the strength to
some extent after the coating baking in the case of attaching great
importance to the formability.
[0004] As described above, more severe molding of aluminum alloy
sheets for molding has been particularly recently often performed.
In addition to severe molding conditions, importance has been
placed on surface appearance quality. With regard to the surface
appearance quality, it is strongly demanded that not only no
Lueders mark is generated but also no ridging mark is generated
even when the severe molding described above is performed.
[0005] The ridging mark is a fine recessed and projected pattern
that appears in a stripe shape in a direction parallel to the
direction of rolling in a step of producing a sheet when the sheet
is molded. Surface appearance quality may be deteriorated because a
site at which such a ridging mark is generated appears as, for
example, a site with less luster or the like even after a sheet
surface is coated. Therefore, a material for an automobile body
sheet or the like particularly requiring high surface appearance
quality strongly requires that a ridging mark is prevented from
being generated in molding. Hereinafter, in this specification,
resistance to generation of a ridging mark in molding is referred
to as "ridging resistance."
[0006] Examples of known aluminum alloys commonly used for
automotive body sheets include an Al--Mg-based alloy, as well as an
Al--Mg--Si-based alloy or Al--Mg--Si--Cu-based alloy with an aging
property. In particular, an Al--Mg--Si-based alloy with an aging
property and an Al--Mg--Si--Cu-based alloy with an aging property
have relatively low strength and improved formability in molding
prior to coating baking, has an advantage of being aged by heating
during the coating baking, thereby enhancing strength after the
coating baking, and has an advantage in that, for example,
generation of a Lueders mark is inhibited.
[0007] As described above, aluminum alloy sheet materials for
molding have required more severe working conditions for press
formability and bending workability. Not only securing of press
formability and bending workability but also ridging resistance for
improving surface appearance quality has been demanded. Various
commitments have also been made to the aluminum alloy sheet
materials described above.
[0008] Drawability and stretchability are required for press
formability. A number of findings for improving the press
formability have been conventionally obtained. In particular, it
has been proposed that press formability is improved by controlling
the amounts of elements added to an aluminum alloy to adjust
strength and increasing a difference between a tensile strength and
a proof stress as well as an elongation in a tensile test (Patent
Literatures 1 and 2).
[0009] It has been pointed out that the bending workability of an
aluminum alloy sheet material is profoundly associated with the
particle sizes of Al--Fe--Si-based particles, Mg--Si-based
particles, or the like which are precipitates in an alloy, and the
texture of the alloy. For example, in Patent Literatures 3 to 6,
proposals are made from the viewpoints of the control of the sizes
of particles and the dispersion state of the particles, and the
control of a texture and an r-value caused by the texture.
[0010] In parallel with such proposals for improvement of
workability as described above, some commitments to improvement of
ridging resistance associated with appearance quality after working
have been reported. According to the commitments, generation of a
ridging mark has been confirmed to be profoundly associated with a
recrystallization behavior in a material. In addition, it has been
proposed as a manner for inhibiting the generation of a ridging
mark that recrystallization is controlled in a process for
producing a sheet by hot rolling and/or the like performed after
homogenization treatment of an alloy ingot.
[0011] As such a specific manner for improving ridging resistance,
for example, a temperature at which hot rolling is started is
principally set at a relatively low temperature of 450.degree. C.
or less, thereby inhibiting crystal grains from coarsening during
hot rolling and then controlling a material structure after cold
working and solution treatment, in Patent Literatures 7 and 8.
Patent Literature 9 mentions differential speed rolling in a warm
region and differential speed rolling in a cold region after hot
rolling. In Patent Literatures 8, 9, and 10, it is proposed that
intermediate annealing is performed after hot rolling, or that cold
rolling is temporarily performed, followed by performing
intermediate annealing.
[0012] In Patent Literatures 10 and 11, it is proposed that
self-annealing is performed by heat in winding of a rolled sheet
that has been hot-rolled, thereby temporarily decomposing a
stripe-shaped structure caused by ingot crystal grains. It is
considered that a sheet material with favorable ridging resistance
can be produced because the stripe-shaped structure is sufficiently
decomposed when recrystallization is re-performed in solution
treatment.
[0013] Patent Literature 12 describes that an alloy ingot is
subjected to homogenization treatment and then to hot rolling into
a rolled material having a thickness of 4 to 20 mm, and the rolled
material is cold-rolled to have a sheet thickness of 2 mm or more
at a sheet thickness reduction rate of 20% or more, thereby
allowing the cube orientation of a sheet material to be
appropriate.
CITATION LIST
Patent Literature
[0014] Patent Literature 1: Unexamined Japanese Patent Application
Kokai Publication No. 2001-342577
[0015] Patent Literature 2: Unexamined Japanese Patent Application
Kokai Publication No. 2002-146462
[0016] Patent Literature 3: Unexamined Japanese Patent Application
Kokai Publication No. 2012-77319
[0017] Patent Literature 4: Unexamined Japanese Patent Application
Kokai Publication No. 2006-241548
[0018] Patent Literature 5: Unexamined Japanese Patent Application
Kokai Publication No. 2004-10982
[0019] Patent Literature 6: Unexamined Japanese Patent Application
Kokai Publication No. 2003-226926
[0020] Patent Literature 7: Japanese Patent No. 2823797
[0021] Patent Literature 8: Japanese Patent No. 3590685
[0022] Patent Literature 9: Unexamined Japanese Patent Application
Kokai Publication No. 2012-77318
[0023] Patent Literature 10: Unexamined Japanese Patent Application
Kokai Publication No. 2010-242215
[0024] Patent Literature 11: Unexamined Japanese Patent Application
Kokai Publication No. 2009-263781
[0025] Patent Literature 12: Unexamined Japanese Patent Application
Kokai Publication No. 2015-67857
SUMMARY OF INVENTION
Technical Problem
[0026] Individual characteristics of press workability, bending
workability, and ridging resistance have been confirmed to be
improved in the techniques for improving the conventional
production processes described above and aluminum alloy sheet
materials for molding produced by the techniques. However, mutual
compatibility among the press workability, the bending workability,
and the ridging resistance is needed for addressing more severe
requirements of improvement in molding characteristics and surface
quality in recent years but is not easily achieved. This is because
the criteria for improving press formability, bending workability,
and ridging resistance described in Patent Literatures 1 to 6 are
not intrinsically designed for satisfying all the three
characteristics.
[0027] With regard to production processes, it is also considered
that, for example, in a case in which additional elements are
controlled for strength adjustment useful for improving press
formability, it may be impossible to apply, to alloy composition
considered to be preferred in the case, criteria as indices for a
production process for improving bending workability and ridging
resistance as well as for a produced sheet material. Even a
production process conventionally considered to be effective is
incapable of having such an effect when a material structure,
particularly the constitution or property of a precipitate, is
changed by adjustment of alloy composition. It is also possible
that the effect of the setting of a temperature at which hot
rolling is started at a relatively low temperature in Patent
Literatures 7 and 8 is not always sufficient when molding
conditions become more severe. The intermediate annealing after hot
rolling performed in Patent Literatures 2, 8, 9, and 10 and the
differential speed rolling in Patent Literature 9 may exhibit no
effect of improving ridging resistance under the alloy composition
made in consideration of the press formability. With regard to the
performance of self-annealing by heat in winding in hot rolling
proposed in Patent Literatures 10 and 11, a precipitate which is
not taken into consideration in these literatures may prevent
recrystallization, thereby precluding the self-annealing. According
to the present inventors, it is impossible to obtain an aluminum
alloy sheet material improved in both bending workability and
ridging resistance even in the case of making such definitions of a
sheet thickness and the like after hot rolling as described in
Patent Literature 12.
[0028] Thus, the present disclosure provides an aluminum alloy
sheet material for molding that can have surface quality after
working while addressing severe molding conditions and that
achieves mutual compatibility among press workability, bending
workability, and ridging resistance.
Solution to Problem
[0029] The present inventors performed intensive examination in
order to solve the problems described above and first found, from
targeted Al--Mg--Si--Cu-based alloys, an aluminum alloy having a
great difference between a tensile strength and a 0.2% proof stress
as an indicator for improvement in press formability. As a result,
there was adopted an aluminum alloy having a Cu concentration of
0.30 mass % (hereinafter simply referred to as "%") or more.
Addition of 0.30% or more Cu to an Al--Mg--Si--Cu-based alloy,
which is an aluminum alloy with an aging property as described
above, enables the alloy to have a higher strength after solution
treatment, regardless of the number of aging days. According to the
present inventors, the Al--Mg--Si--Cu-based alloy can have a great
difference between a tensile strength and a 0.2% proof stress as
well as a high strength, and can have press formability.
[0030] Thus, the present inventors examined means of allowing
compatibility between the bending workability and anti-ridging
property of an alloy sheet material on the basis of securing of
press formability by application of the Al--Mg--Si--Cu-based alloy
to which 0.30% or more Cu is added. The present inventors
considered that items associated closely with the means include
behaviors and features in a process of producing an
Al--Mg--Si--Cu-based alloy sheet.
[0031] According to the examination by the present inventors,
Mg--Si-based particles as precipitates are very finely precipitated
as particles containing Cu (Mg--Si--Cu-based particles) in a
production step prior to hot rolling, in an Al--Mg--Si-based alloy
sheet material containing Cu. The precipitation of the
Mg--Si--Cu-based particles occurs in a cooling process after
homogenization treatment, a heating process until reaching a
hot-rolling temperature, and a heating and retention process until
the start of the hot rolling. When the state of fine dispersion of
Mg--Si--Cu-based particles is not addressed, even hot rolling does
not enable the fine precipitates to function as the origin of a
recrystallized structure, but rather causes recrystallization to be
suppressed. Therefore, a state occurs in which hot rolling does not
cause an expected recrystallized structure or in which even if
recrystallization occurs, a very coarse recrystallized structure is
generated and ridging resistance is not improved.
[0032] The structure of such a hot-rolled material with
recrystallization insufficient due to the influence of fine
precipitates as described above is not sufficiently improved even
by setting a temperature at which a rolled sheet that has been
hot-rolled is wound at 300.degree. C. or more and by performing
self-annealing of the hot-rolled material, as in the conventional
technologies (Patent Literatures 10 and 11) described above. Any
effect caused by intermediate annealing after the hot rolling is
incapable of being expected.
[0033] Thus, the present inventors tried to control the state of
the distribution of Mg--Si--Cu-based particles in an
Al--Mg--Si--Cu-based alloy sheet material. In this examination, the
features of the Mg--Si--Cu-based particles were summarized as
follows.
[0034] (a) The state of the precipitation of Mg--Si--Cu-based
particles is influenced by a cooling rate after homogenization
treatment. When the cooling rate after the homogenization treatment
is high, the precipitation of the Mg--Si--Cu-based particles occurs
at a lower temperature, and particle sizes become smaller. In
addition, the amounts of Mg, Si, and Cu taken in solid solution
states are increased, and therefore, fine precipitation further
occurs in subsequent heating.
[0035] (b) When an ingot of an aluminum alloy is heated to a
hot-rolling temperature and retained, the Mg--Si--Cu-based
particles precipitated after the homogenization treatment are
coarsened in the processes of the heating and the retention.
[0036] (c) The state of the precipitation of the Mg--Si--Cu-based
particles in (a) and the rate of the coarsening by the heating in
(b) as described above are influenced by the content of Cu in the
aluminum alloy. Specifically, an increase in the content of Cu
tends to cause the Mg--Si--Cu-based particles to be finer. In
addition, the rate of the coarsening of the Mg--Si--Cu-based
particles by the heating is decreased with increasing the content
of Cu. These actions due to Cu tend to become noticeable when the
content of Cu is 0.30 mass % or more. For example, the coarsening
rate of Mg--Si--Cu-based particles in an Al--Mg--Si--Cu-based alloy
with 0.30% or more Cu is much lower than the coarsening rate of
Mg--Si--Cu-based particles precipitated in an Al--Mg--Si-based
alloy with less than 0.30% Cu.
[0037] On the basis of the findings of (a), (b), and (c) described
above, examples of manners for controlling the state of the
distribution of Mg--Si--Cu-based particles include, first,
decreasing a cooling rate after homogenization treatment on the
basis of the findings of (a). This manner is a manner for
inhibiting the precipitation itself of fine Mg--Si--Cu-based
particles. Decreasing a cooling rate after homogenization treatment
can be mentioned on the basis of the findings of (a).
[0038] Coarsening of fine Mg--Si--Cu-based particles into
appropriate sizes by intentional heating and retention at a
temperature close to a hot-rolling temperature after homogenization
treatment is also considered to be effective on the basis of the
findings of (b). The precipitation of fine Mg--Si--Cu-based
particles is not always able to be completely inhibited even if the
cooling rate after the homogenization treatment is lowered. A case
in which it is impossible to lower the cooling rate after the
homogenization treatment can also be considered from the viewpoint
of a production facility, production control, or the like. Thus,
treatment of retaining an ingot of an aluminum alloy at a
temperature close to the hot-rolling temperature enables the
Mg--Si--Cu-based particles to be coarsened, and this manner can be
considered to be a particularly effective manner.
[0039] On the basis of the findings of (c), it is necessary to
strictly consider both of the state and rate of the precipitation
of Mg--Si--Cu-based particles in the case of an aluminum alloy
containing 0.30% or more Cu according to the present disclosure. In
particular, it is required to appropriately examine the setting of
the time of the heating and retention described above according to
the content of Cu in consideration of the diffusion of Cu.
[0040] In the present disclosure, a precipitate is controlled as
described above in an Al--Mg--Si--Cu-based alloy sheet material to
which 0.30% or more Cu is added, the material is then hot-rolled,
and self-annealing is thereafter performed by winding the material
at an appropriate temperature. The thereby produced
Al--Mg--Si--Cu-based alloy sheet material has improved press
formability, includes an appropriately controlled texture, and also
has improved bending workability. Further, the material also has
improved ridging resistance. The present inventors revealed, as the
constitutions of the Al--Mg--Si--Cu-based alloy sheet material with
the improved various characteristics, the mechanical properties of
the sheet material, as well as a relationship between a cube
orientation density and a random orientation, and the deviation of
an average Taylor factor in a predetermined plane of the sheet
material, and arrived at the present disclosure.
[0041] In other words, the present disclosure provides an aluminum
alloy rolled material for molding, with improved press formability,
bending workability, and ridging resistance, the aluminum alloy
rolled material including: an aluminum alloy including 0.30 to
1.50% Cu, 0.30 to 1.50% Si, 0.30 to 1.50% Mg, at least one of 0.50%
or less Mn, 0.40% or less Cr, or 0.40% or less Fe, and a balance of
Al and inevitable impurities, wherein a difference between a
tensile strength and a 0.2% proof stress is 120 MPa or more,
wherein a ratio of a cube orientation density to a random
orientation is 10 or more in a plane that is perpendicular to a
sheet thickness direction and is at a depth of 1/4 of a total sheet
thickness from a surface, and wherein an absolute value of a
difference between a maximum value and a minimum value of an
average Taylor factor in a case in which molding is assumed to
cause plane strain deformation having a main strain direction that
is a rolling width direction is 1.0 or less, the average Taylor
factor being obtained for each of subareas that are obtained by
equal division of an area, having a 10 mm width in the rolling
width direction and a 2 mm length in a rolling direction, into 10
subareas in the rolling width direction, the subareas being in a
plane that is perpendicular to the sheet thickness direction and is
at a depth of 1/2 of the total sheet thickness from the
surface.
[0042] The aluminum alloy rolled material according to the present
disclosure may contain at least one of 0.03 to 0.50% Mn, 0.01 to
0.40% Cr, or 0.03 to 0.40% Fe, and may further contain at least one
of 0.03 to 0.15% Mn, 0.01 to 0.04% Cr, or 0.03 to 0.40% Fe.
[0043] In the aluminum alloy rolled material of the present
disclosure, the difference between the tensile strength and the
0.2% proof stress is preferably 121 to 133 MPa.
[0044] In the aluminum alloy rolled material of the present
disclosure, the ratio of the cube orientation density to the random
orientation is preferably 12 or more, and still more preferably 12
to 18.
[0045] In the aluminum alloy rolled material of the present
disclosure, the absolute value of the difference between the
maximum value and the minimum value of the average Taylor factor is
preferably 0.9 or less, and preferably 0.5 to 0.9.
[0046] In the aluminum alloy rolled material of the present
disclosure, a score given by comparison with workability evaluation
samples is 6 or more, preferably 7 or more, and still more
preferably 8 or more, in 180-degree bending working.
[0047] In the aluminum alloy rolled material of the present
disclosure, the aluminum alloy rolled material is obtained by
rolling working including hot rolling working, and an average
particle size of precipitated particles having particle diameters
of 0.4 to 4.0 .mu.m is preferably 0.6 .mu.m or more, and preferably
0.7 to 1.9 .mu.m, in pre-rolling heating and retention prior to the
hot rolling working.
[0048] In the aluminum alloy rolled material of the present
disclosure, a density of the precipitated particles having particle
diameters of 0.4 to 4.0 .mu.m, is preferably equal to or less than
1500 particles/100 .mu.m.sup.2, and preferably 402 particles/100
.mu.m.sup.2 to 1411 particles/100 .mu.m.sup.2.
[0049] In the aluminum alloy rolled material of the present
disclosure, a recrystallization rate after the hot rolling working
is preferably 95% or more, and more preferably 100%.
Advantageous Effects of Invention
[0050] The aluminum alloy rolled material according to the present
disclosure is an aluminum alloy rolled material that is produced by
controlling Mg--Si--Cu-based particles precipitated in a sheet
production process while setting the amount of added Cu to 0.30% or
more in an Al--Mg--Si-based alloy containing Cu and that has
compatibility among high press formability, ridging resistance, and
bending workability.
BRIEF DESCRIPTION OF DRAWINGS
[0051] FIG. 1 is an explanatory diagram of planes (plane S2 and
plane S3) that define the texture of an aluminum alloy rolled
material according to the present disclosure; and
[0052] FIG. 2 is an external view of samples for evaluation of
bending test results in an embodiment of the present
application.
DESCRIPTION OF EMBODIMENTS
[0053] An embodiment of an aluminum alloy rolled material according
to the present disclosure will be specifically described below. In
the following discussion, the alloy composition and mechanical
characteristics of an aluminum alloy included in the aluminum alloy
rolled material according to the present disclosure will first be
described, and then the features of a texture will be described. A
method preferred for producing the aluminum alloy rolled material
according to the present disclosure will also be described in
detail.
[0054] (1) Alloy Composition of Aluminum Alloy Rolled Material
According to the Present Disclosure
[0055] As described above, the aluminum alloy rolled material
according to the present disclosure is based on an aluminum alloy
comprising Cu, Si, and Mg as essential additional elements, further
at least one of Cr, Mn, or Fe, and a balance of Al and inevitable
impurities. The action and addition amount of each additional
element will be described below.
[0056] Cu: 0.30 to 1.50%
[0057] Cu is a fundamental alloy element in the alloy system of the
present disclosure and contributes to improvement in strength in
cooperation with Si and Mg described later. As described above, it
is important to define the amount of added Cu in the aluminum alloy
rolled material according to the present disclosure from the
viewpoint of improvement in press formability. In other words, in
the present disclosure, an alloy sheet is allowed to have a high
strength after solution treatment by setting the amount of added Cu
to 0.30% or more, and press formability is secured by setting a
great difference between a tensile strength and a 0.2% proof
stress. A Cu amount of less than 0.30% causes such effects to be
insufficient. With regard to an upper limit, an amount of more than
1.50% results in degradation in corrosion resistance (intergranular
corrosion resistance and filiform corrosion resistance). From the
above viewpoints, the content of Cu is set within a range of 0.30
to 1.50%. The lower limit value, a Cu amount of 0.30%, has
significances as a criterion for securing of press formability and
as a criterion for showing the possibility or impossibility of
compatibility between a relationship between a cube orientation
density and a random orientation described later and the deviation
of an average Taylor factor.
[0058] Si: 0.30 to 1.50%
[0059] Si is a fundamental alloy element in the alloy system of the
present disclosure and contributes to improvement in strength in
cooperation with Mg and Cu. The above-described effects are not
sufficiently obtained when the amount of Si is less than 0.30%,
while coarse Si particles and coarse Mg--Si--Cu-based particles are
generated, resulting in the deterioration of press formability,
particularly bending workability, when the amount of Si is more
than 1.50%. Accordingly, the amount of Si is set within a range of
0.30 to 1.50%. A Si amount within a range of 0.60 to 1.30% is
preferred for allowing a balance between press formability and
bending workability to be more favorable.
[0060] Mg: 0.30 to 1.50%
[0061] Mg is also a fundamental alloy element in the alloy system
as a subject of the present disclosure and contributes to
improvement in strength in cooperation with Si and Cu. The amount
of a generated G.P. zone which contributes to improvement in
strength due to precipitation hardening in coating baking becomes
small, and therefore a sufficient improvement in strength is not
obtained when the amount of Mg is less than 0.30%, while coarse
Mg--Si--Cu-based particles are generated, resulting in the
deterioration of press formability, particularly bending
workability, when the amount of Mg is more than 1.50%. Thus, the
amount of Mg is set within a range of 0.30 to 1.50%. A Mg amount
within a range of 0.30 to 0.80% is preferred for allowing the press
formability, particularly bending workability, of a final sheet to
be more favorable.
[0062] Mn: 0.50% or less, Cr: 0.40% or less
[0063] Mn and Cr are elements effective at allowing crystal grains
to be finer and at stabilizing a structure. However, a Mn content
of more than 0.50% or a Cr content of more than 0.40% may cause not
only saturation of the above-described effects but also generation
of a large number of intermetallic compounds, resulting in an
adverse impact on formability, particularly hem-bendability.
Accordingly, Mn is set at 0.50% or less, and Cr is set at 0.40% or
less. With regard to the lower limit values of the contents of Mn
and Cr, when the content of Mn is less than 0.03% or the content of
Cr is less than 0.01%, the above-described effects are not
sufficiently obtained, crystal grains are coarsened in solution
treatment, and a surface may be roughened in hemming-bending. Thus,
the contents of Mn and Cr are preferably set at Mn: 0.03 to 0.50%
and Cr: 0.01 to 0.40%.
[0064] With regard to Mn and Cr, more than 0.15% Mn or more than
0.05% Cr may result in an excessive increase in the above-described
effects and in inhibition of recrystallization in self-annealing
after hot-rolling winding. Thus, further restrictions on Mn and Cr
may be preferred in consideration of a balance with other
additional elements. In such a case, Mn is more preferably 0.03% or
more and 0.15% or less. Cr is more preferably 0.01% or more and
0.05% or less.
[0065] Fe: 0.40% or less
[0066] Fe is also an element effective at improving strength and
allowing crystal grains to be finer, but more than 0.40% Fe may
cause a large number of intermetallic compounds to be generated and
bending workability to be deteriorated. Thus, the amount of Fe is
set at 0.40% or less. With regard to the lower limit of the amount
of Fe, an Fe amount of less than 0.03% may result in an
insufficient effect. Thus, it is preferable to set the amount of Fe
within a range of 0.03 to 0.40%. It is more preferable to set the
amount of Fe at 0.03% to 0.20% when further bending workability is
demanded.
[0067] The aluminum alloy in the present disclosure may
fundamentally comprise Al and inevitable impurities as well as Si,
Mg, Cu, Cr, Mn, and Fe described above. Examples of the inevitable
impurities include Zn, Ti, and V. The effects of the present
disclosure are prevented from deteriorating when Zn is 0.30% or
less, the elements other than Zn are 0.10% or less, all the
impurity elements other than Zn are 0.20% or less.
[0068] (2) Mechanical Characteristics of Aluminum Alloy Rolled
Material According to the Present Disclosure
[0069] A greater difference between a tensile strength and a 0.2%
proof stress is effective at improving the press formability of an
aluminum alloy rolled material, as described above. The difference
between these values relating to mechanical characteristics
corresponds to an allowance against rupture after the start of
plastic deformation and the proceeding of local deformation.
Therefore, formability can be improved by increasing the difference
between the tensile strength and the 0.2% proof stress.
Specifically, the aluminum alloy rolled material according to the
present disclosure has a difference between a tensile strength and
a 0.2% proof stress of 120 MPa or more. An aluminum alloy rolled
material of which the value of the difference is less than 120 MPa
results in insufficient formability under severer press molding
conditions in recent years. The difference between the tensile
strength and the 0.2% proof stress is preferably 121 to 133 MPa.
The tensile strength is preferably 225 MPa or more.
[0070] As already mentioned, in the aluminum alloy rolled material
according to the present disclosure, an Al--Mg--Si--Cu-based alloy
is adopted, and the difference between the tensile strength and the
0.2% proof stress of an alloy sheet is allowed to be 120 MPa or
more by adding 0.30% or more Cu. The positive addition of Cu
results in the effect of changing the state of a fine cluster
formed after solution treatment and greatly improving work
hardening characteristics. A common Al--Mg--Si-based alloy for an
automobile panel, to which Cu is not positively added, has a
difference between a tensile strength and a 0.2% proof stress of
115 MPa or less.
[0071] (3) Texture of Aluminum Alloy Rolled Material According to
the Present Disclosure
[0072] The aluminum alloy rolled material produced by the method
according to the present disclosure includes favorable
characteristics in ridging resistance and bending workability as
well as press formability. The aluminum alloy rolled material
includes a texture exhibiting distinguishing characteristics.
Specifically, the aluminum alloy rolled material includes features
relating to each of a relationship between a cube orientation
density and a random orientation, and the deviation of an average
Taylor factor in a predetermined plane of the aluminum alloy sheet
material, and also has both the indices thereof in preferred
ranges. Each characteristic will be described below.
[0073] (3.1) Texture Based on Cube Orientation Density as Index,
and Bending Workability
[0074] In the aluminum alloy rolled material according to the
present disclosure, the constituent composition of an alloy is
adjusted as described above, and the texture of the aluminum alloy
rolled sheet as a final sheet is appropriately controlled based on
a cube orientation density as an index. This is because, in
particular, bending workability is improved stably. The cube
orientation density is the orientation density of a crystal grain
with a cube orientation ({100}<001> orientation). In the
present disclosure, specifically, it is necessary that the ratio of
the cube orientation density to a random orientation is 10 or more
in a plane that is perpendicular to a sheet thickness direction and
is at a depth of 1/4 of a total sheet thickness from a surface.
Crystal grains with a cube orientation inhibit a shear zone from
being generated in hemming-bending and inhibit a bending crack from
occurring and propagating along a shear zone. The bending
workability can be improved by increasing the rate of cube
orientation crystal grains inhibiting the formation and propagation
of a shear zone by controlling the ratio of the cube orientation
density to 10 or more. The ratio of the cube orientation density is
preferably set at 12 or more, and more preferably at 12 to 18, in
order to achieve further strict appearance quality after bending
working.
[0075] The reason that the texture in the plane that is
perpendicular to a sheet thickness direction and is at a depth of
1/4 of a total sheet thickness from a surface is defined as a
reference of improvement in bending workability is because the
vicinity of a surface layer of a sheet particularly influences
surface quality under a very severe working condition,
hemming-bending, according to the present inventors.
[0076] The measurement of a cube orientation density will be
specifically described with reference to FIG. 1. First, a plane S2
that is perpendicular to a sheet thickness direction T and is at a
depth of 1/4 of a total sheet thickness t from a sheet surface S1
is exposed by mechanical polishing. Then, the orientation
information of a texture is acquired by measuring the incomplete
pole figures of a (111) plane, a (220) plane, and a (200) plane by
reflection method of Schulz which is one of X-ray diffraction
measurement methods at an inclination angle ranging from 15 to
90.degree.. The cube orientation density can be determined based on
the obtained orientation information of the texture by using pole
figure analysis software.
[0077] For example, analysis software "Standard ODF" publicly
distributed by Hirofumi Inoue [Associate Professor] in Osaka
Prefecture University or "OIM Analysis" manufactured by 1TSL may be
used as the analysis software. Specifically, first, the orientation
information of the texture obtained by the above-described method
is subjected to rotation operation as needed and to series
expansion on the conditions that the expansion degrees of "even
number term" and "odd number term" are "22" and "19", respectively,
thereby determining a crystal orientation distribution function
(ODF). The orientation density of each orientation obtained by the
ODF can be calculated as a ratio with respect to the orientation
density of a standard sample including a random texture obtained by
sintering an aluminum powder (random ratio).
[0078] (3.2) Texture Based on Taylor Factor as Index, and Ridging
Resistance
[0079] In the present disclosure, ridging resistance as well as
press formability and bending workability is improved, and such
preferably balanced characteristics are achieved. It is very
important to appropriately control the texture of the aluminum
alloy rolled material which is a final sheet on the basis of a
Taylor factor as an index with regard to the ridging resistance. In
other words, high-level ridging resistance can be achieved by
controlling the texture so that the dispersion of average Taylor
factors in a rolling width direction is within an appropriate
range.
[0080] A ridging mark is a fine recessed and projected pattern that
is generated in a stripe shape in a direction parallel to a rolling
direction when a rolled sheet is molding-worked. The generation of
the ridging mark is considered to be caused by a difference between
the plastic deformation amounts of crystal orientations adjacent to
each other in molding.
[0081] The actual strain state of a press molded component in the
case of press molding of a rolled sheet is known to be distributed
primarily in a region between a plane strain state and an
equibiaxial strain state. It is considered that a ridging mark is
most prominently generated due to the plane strain, of which the
rolling width direction (direction perpendicular to a rolling
direction and parallel to a sheet surface) is a main strain
direction, of the strains in the region. The plane strain
deformation in the rolling width direction can be considered to be
a strain state in which only an extension in the rolling width
direction and a decrease in sheet thickness occur.
[0082] The dispersion (fluctuation range) of Taylor factor values
in a rolling width direction in a case in which molding is assumed
to cause plane strain deformation having a main strain direction
that is a rolling width direction is an effective index for ridging
resistance. The Taylor factors are calculated from all crystal
orientations existing in the texture, and the reduction of the
dispersion of Taylor factors in a rolling width direction in a case
in which molding is assumed to cause plane strain deformation
having a main strain direction that is the rolling width direction
in a sheet surface of the rolled sheet or a plane in a sheet
parallel to the sheet surface is effective for improving ridging
resistance.
[0083] In the present disclosure, in the control of a texture based
on a Taylor factor as an index, the absolute value of the
difference between the maximum value and the minimum value of the
average Taylor factor in a case in which molding is assumed to
cause plane strain deformation having a main strain direction that
is a rolling width direction is 1.0 or less. The average Taylor
factor is obtained for each of subareas that are obtained by equal
division of an area, having a 10 mm width in the rolling width
direction and a 2 mm length in a rolling direction, into 10
subareas in the rolling width direction. The subareas are in a
plane that is perpendicular to the sheet thickness direction and is
at a depth of 1/2 of the total sheet thickness from the surface.
The absolute value of the difference between the maximum value and
the minimum values of the average Taylor factors is preferably 0.9
or less.
[0084] The index will be specifically described with reference to
FIG. 1. FIG. 1 clearly illustrates three planes S1, S2, and S3
which are a sheet surface S1 that is perpendicular to a sheet
thickness direction T, a plane S2 that is perpendicular to the
sheet thickness direction T and is at a depth of 1/4 of a total
sheet thickness t from the sheet surface S1, and a plane S3 that is
perpendicular to the sheet thickness direction T and is at a depth
of 1/2 of the total sheet thickness t from the sheet surface S1. In
the present disclosure, in the plane S3 among the planes, an area
SA having a 10 mm width in a rolling width direction Q and a 2 mm
length in a rolling direction P is made in an arbitrary site in the
plane, subareas SA1, SA2, . . . , SA10 in the same plane are
obtained by equal division of the area SA into 10 subareas in the
rolling width direction Q, and the value of the average Taylor
factor of each of the subareas SA1, SA2, . . . , SA10 is measured.
The average value of Taylor factors in a case in which molding is
assumed to cause plane strain deformation having a main strain
direction that is the rolling width direction Q is measured as
described above. A ridging mark can be stably inhibited from being
generated in the molding by controlling the absolute value of the
difference between the maximum value and the minimum value of the
measurement values of the corresponding subareas SA1, SA2, . . . ,
SA10 to be 1.0 or less, that is, by reducing the maximum value of
the dispersion of the values of the average Taylor factors of the
micro-areas (the corresponding subareas SA1, SA2, . . . , SA10) in
the plane S3 in the rolling width direction to 1.0 or less.
[0085] In contrast, when the absolute value of the difference
between the maximum value and the minimum value of the values of
the average Taylor factors of the corresponding subareas SA1, SA2,
. . . , SA10 defined as described above is more than 1.0, the local
dispersion of plastic deformation amounts in the rolling width
direction becomes noticeable, ridging resistance is deteriorated,
and a ridging mark may be generated.
[0086] In the present disclosure, the area SA having a 10 mm width
in the rolling width direction and a 2 mm length in the rolling
direction is set, and the subareas obtained by equal division of
the area into 10 subareas in the rolling width direction are
targets for the measurement of the average Taylor factors. The
difference between the maximum value and the minimum value of the
average Taylor factors measured in the corresponding subareas is
regarded as an index for evaluating ridging resistance. The
validity of the settings of the shapes, dimensions, and division
number of the areas of the measurement of the average Taylor
factors was confirmed by the present inventors. The present
inventors confirmed by experiment that ridging resistance can be
reliably and effectively evaluated based on the settings.
[0087] In the present disclosure, the maximum value of the
dispersion of the average Taylor factors in the rolling width
direction is defined only in the plane S3, that is, the plane
located in the center of the sheet thickness. The reason that only
the presence or absence of the dispersion of the average Taylor
factors in the plane S3 is regarded as the index for evaluating
ridging resistance is because it is preferable to determine the
presence or absence of the generation of a ridging mark on the
basis of the state of crystals in the area. Like the plane S3, the
states of crystals in the sheet surface (plane S1) and the plane
(plane S2) at a depth of 1/4 of the total sheet thickness can also
influence the generation of a ridging mark, and a band-shaped
structure which influences the generation of a ridging mark remains
most easily in the vicinity of the center of the sheet thickness.
Accordingly, an aluminum alloy rolled material can be considered to
be improved in ridging resistance intended by the present
disclosure by allowing the state of the crystals of the plane S3 to
be a favorable state and confirming the state. The reason that the
maximum value of the dispersion of the average Taylor factors is
regarded as the index is because the present disclosure is intended
to decompose a band-shaped structure, and the index is preferred
for evaluating the state of a formed texture on the basis of the
success or failure thereof.
[0088] Accordingly, the present disclosure does not deny that
subareas are set in the plane S1 and the plane S2 like plane S3 and
the dispersion of Taylor factors is measured. Further, it is not
intended to exclude that the results of the dispersion of the
Taylor factors in the plane S1 and the plane S2 are equivalent to
or better than the results of the dispersion of the plane S3
required by the present disclosure.
[0089] A specific method for measuring an average Taylor factor
value in each of the predetermined subareas in the plane S3 that is
perpendicular to the sheet thickness direction and is at a depth of
1/2 of the total sheet thickness from the sheet surface S1 will now
be described. First, the surface S3 at a depth of 1/2 of the total
sheet thickness which becomes a measurement plane is exposed. This
exposure can be performed by mechanical polishing,
buffing-polishing, or electrolytic polishing. The orientation
information of the texture is acquired by measuring each of the
predetermined subarea ranges continuous in the rolling width
direction in the exposed plane S3 per visual field with a
backscattered electron diffraction measurement apparatus attached
to a scanning electron microscope (SEM-EBSD). A STEP size for the
measurement may be set at around 1/10 of a crystal particle
diameter.
[0090] An average Taylor factor is determined from the obtained
orientation information using EBSD analysis software. For example,
"OIM Analysis" manufactured by TSL may be used as the analysis
software. Specifically, first, the orientation information of the
texture obtained by the above-described method is subjected to
rotation operation as needed so that measurement data shows the
orientation information in the case of being viewed from the sheet
thickness direction. Then, average Taylor factors in the
corresponding subareas can be calculated by calculating an average
Taylor factor under a plane strain state in which the sheet
thickness decreases and the rolling width direction extends on a
measurement data basis in each visual field. The calculation can be
performed on the assumption that an active primary slip system is
{111}<110>. The average Taylor factors in the corresponding
subareas are calculated in such a manner, and the difference
between the maximum and minimum values of the average Taylor
factors is calculated, thereby evaluating ridging resistance.
[0091] (4) Production Method Preferred for Aluminum Alloy Rolled
Material According to the Present Disclosure
[0092] A preferred method for producing an aluminum alloy rolled
material according to the present disclosure will now be described.
The aluminum alloy rolled material according to the present
disclosure is a sheet material that comprises an
Al--Mg--Si--Cu-based alloy and includes an optimized texture. The
state of the distribution of Mg--Si--Cu-based particles is
preferably controlled in a sheet production process to adjust a
recrystallized structure after hot rolling in order to obtain such
a preferred texture, as described above. According to the present
inventors, examples of a method for controlling the state of the
distribution of the Mg--Si--Cu-based particles include
appropriately setting a cooling rate after homogenization treatment
and intentionally retaining, at a hot-rolling temperature, an ingot
after the homogenization treatment. The retention at the
hot-rolling temperature enables the Mg--Si--Cu-based particles to
be coarsened and an origin for causing a preferred recrystallized
structure to be formed. Fine recrystallization can be achieved by
self-annealing using heat generated in the case of winding of a
rolled material in a subsequent hot-rolling step.
[0093] In other words, examples of the preferable method for
producing the aluminum alloy rolled material according to present
disclosure include a method for producing an aluminum alloy rolled
material for molding, the method including: a step of performing
homogenization treatment of an ingot including an aluminum alloy
including the composition described above; a cooling step of
cooling the aluminum alloy after the homogenization treatment so
that an average cooling rate in a thickness of 1/4 part from a
surface of the ingot between 500.degree. C. and a cooling
temperature is 20.degree. C./h to 2000.degree. C./h, the cooling
temperature being set at a temperature of more than 320.degree. C.
or at a temperature of 320.degree. C. to room temperature; and a
step of starting hot rolling at 370.degree. C. to 440.degree. C.
and winding the hot-rolled aluminum alloy at 310 to 380.degree. C.,
wherein the aluminum alloy after the cooling step is retained at a
pre-rolling heating temperature set within a range of 370.degree.
C. to 440.degree. C. before the hot rolling, thereby controlling
the sizes of the precipitated particles of the aluminum alloy. The
method for producing the aluminum alloy rolled material will be
described below.
[0094] First, the aluminum alloy with the constituent composition
described above is melted according to a usual method, and cast by
selecting a usual casting method such as a continuous casting
method or a semi-continuous casting method (DC casting method) as
appropriate. The obtained ingot is subjected to homogenization
treatment. Treatment conditions in the case of performing the
homogenization treatment are not particularly limited, but heating
may be performed typically at a temperature of 500.degree. C. or
more and 590.degree. C. or less for 0.5 hour or more and 24 hours
or less.
[0095] The ingot subjected to the homogenization treatment is
cooled and hot-rolled. In the method for producing an aluminum
alloy rolled material according to the present disclosure, it is
needed to define the range of a cooling rate after the stage of
ending the homogenization treatment and to intentionally retain the
ingot at a set pre-rolling heating temperature for not less than a
predetermined time before starting the hot rolling after cooling
the ingot. With regard to the cooling rate after the stage of
ending the homogenization treatment, the cooling is performed so
that an average cooling rate at a temperature of from 500.degree.
C. to a cooling temperature in a thickness of 1/4 part from a
surface of the ingot is between 20.degree. C./h and 2000.degree.
C./h. In such a case, the cooling temperature is a temperature of
more than 320.degree. C. or a temperature of 320.degree. C. to room
temperature. The reason that the cooling rate after the
homogenization treatment is defined as described above is because
an excessively high cooling rate tends to result in precipitation
of fine Mg--Si--Cu-based particles. In addition, this is because an
excessively low cooling rate results in the precipitation of
Mg--Si--Cu-based particles having coarse sizes equal to or larger
than sizes necessary for promoting recrystallization and in the
need for wasting time for making the particles into a solid
solution in final heat treatment (in solution treatment). It is
preferable to set the cooling rate at 50.degree. C./h to
1000.degree. C./h.
[0096] In the present disclosure, a position at which the
temperature of the ingot is measured is set at a thickness of 1/4
part from the surface in the measurement of the cooling rate (the
same applies hereafter). In addition, a position at which the
temperature of the ingot is measured is also set at a thickness of
1/4 part in the case of temperature management in retention at a
pre-rolling heating temperature described later. This is because
the temperature of a surface layer of the ingot widely changes, and
therefore, it is difficult to appropriately measure the cooling
rate. Although stable temperature measurement is also possible in
the center of the ingot, a delay in temperature change may occur to
some degree, and an ingot thickness of 1/4 part is preferred in
consideration of strict management of the cooling rate or the
retention time. The temperature in an ingot thickness of 1/4 part
may be measured using an ingot in which a thermocouple is embedded
or may be calculated using a heat transfer model. The temperature
of an ingot in the following description means the temperature in
an ingot thickness of 1/4 part.
[0097] On the basis of the temperature of the ingot after the
cooling step, plural patterns can be adopted for the heat history
of the ingot after the cooling after the homogenization treatment.
First, the ingot is cooled from the homogenization treatment
temperature so as to be prevented from being cooled to 320.degree.
C. or less, and the ingot is then retained at a pre-rolling heating
temperature set within a range of 370.degree. C. to 440.degree. C.
before the hot rolling. In such a case, the ingot may be retained
at the pre-rolling heating temperature when the temperature of the
ingot reaches the pre-rolling heating temperature from the
homogenization treatment temperature. It is preferable to slightly
heat the ingot to the pre-rolling heating temperature and retain
the ingot when the ingot is cooled to a temperature of more than
320.degree. C. and less than the pre-rolling heating temperature.
The reason that the temperature of the ingot after the cooling step
is based on 320.degree. C. as described above is because fine
Mg--Si--Cu-based particles are inhibited from precipitating.
Accordingly, in view of heat and energy, it is effective to cool
the ingot from the homogenization treatment temperature to more
than 320.degree. C., particularly to a hot-rolling temperature in a
straight manner, in the cooling step after the homogenization
treatment.
[0098] However, the ingot may be temporarily cooled to a
temperature in a range of 320.degree. C. to room temperature in the
cooling step. Even when the ingot is temporarily cooled to the
temperature in a range of 320.degree. C. to the room temperature,
fine Mg--Si--Cu-based particles can be coarsened by re-heating the
ingot to the pre-rolling heating temperature and retaining the
ingot at the pre-rolling heating temperature. Thus, the ingot with
such a heat history is not problematic at all for producing a fmal
sheet of an aluminum alloy with improved ridging resistance and
bendability. The temporal cooling of the ingot to the temperature
in a range of 320.degree. C. to the room temperature and the
re-heating of the ingot are useful for obtaining stable product
characteristics. When such re-heating is performed, time is needed
for coarsening Mg--Si--Cu-based particles as represented by a heat
history coefficient in Equation A described later; however, due to
the time, excessive coarsening is inhibited even in the case of
retention for long time at the pre-rolling heating temperature. As
a result, the deterioration of strength characteristics and bending
workability caused by incompletely melting coarse particles in
solution treatment is inhibited.
[0099] In the present disclosure, the ingot is preferably retained
at the pre-rolling heating temperature set within a range of
370.degree. C. to 440.degree. C. before starting the hot rolling.
Mg--Si--Cu-based particles can be grown and coarsened by the
retention at the pre-rolling heating temperature.
[0100] The reason that the pre-rolling heating temperature is set
at 370.degree. C. to 440.degree. C. is because the temperature is
needed for coarsening finely precipitated Mg--Si--Cu-based
particles. When the temperature is less than 370.degree. C., an
element diffusion length becomes insufficient, and it is impossible
to obtain a preferred particle size. When the temperature is more
than 440.degree. C., coarse recrystallized grains are formed in hot
rolling, and ridging resistance is deteriorated. The range of the
pre-rolling heating temperature is the same as the range of the
hot-rolling temperature. Accordingly, the pre-rolling heating
temperature and the hot-rolling temperature may be set at the same
temperature. In such a case, the ingot after the cooling step is
retained at the hot-rolling temperature, and the hot rolling of the
ingot can be started on an as-is basis. The pre-rolling heating
temperature and the hot-rolling temperature may also be set at
different temperatures. In such a case, the ingot heated and
retained at the pre-rolling heating temperature is cooled or
re-heated, and the hot rolling of the ingot is then started.
However, even a case in which the pre-rolling heating temperature
and the hot-rolling temperature are set at different temperatures
is not problematic if both of the temperatures are set in a range
of 370.degree. C. to 440.degree. C. As described above, the
temperature of the ingot is a temperature in a thickness of 1/4
part from a surface of the ingot.
[0101] The optimal range of the retention time at the pre-rolling
heating temperature is considered to exist depending on various
conditions such as the composition of the aluminum alloy and the
heat history after the homogenization treatment. Examples of the
conditions include, first, the content of Cu in the aluminum alloy.
This is because the dispersion state and coarsening rate of
Mg--Si--Cu-based particles vary depending on the content of Cu as
described above.
[0102] Examples of the conditions that can determine the retention
time also include the heat history of the aluminum alloy after the
homogenization treatment. The heat history is either the history of
retaining the aluminum alloy at the pre-rolling heating temperature
so that the aluminum alloy is prevented from being cooled to
320.degree. C. or less after the homogenization treatment or the
history of cooling the aluminum alloy to a temperature in a range
of 320.degree. C. to room temperature after the homogenization
treatment, then re-heating the aluminum alloy to the pre-rolling
heating temperature, and retaining the aluminum alloy at the
pre-rolling heating temperature.
[0103] Further, the retention time at the pre-rolling heating
temperature can also be determined by a cooling rate after the
homogenization treatment (the average cooling rate of the ingot
between 500.degree. C. and the cooling temperature).
[0104] The present inventors found preferred retention time in
consideration of the various conditions. The retention time at the
pre-rolling heating temperature is preferably set at not less than
the lower limit of a retention time (h) calculated by Equation A
described below.
Lower limit of retention time(h)=3(h).times.Cu amount
coefficient.times.cooling rate coefficient.times.temperature
history coefficient (Equation A)
[0105] wherein the meanings of the Cu amount coefficient, the
cooling rate coefficient, and the temperature history coefficient
in Equation A are described as follows: [0106] Cu amount
coefficient: Cu content (%) in aluminum alloy/reference Cu content
(0.7%); [0107] cooling rate coefficient: (average cooling rate
(.degree. C./h) in cooling step/reference cooling rate (90.degree.
C./h)).sup.1/2; and [0108] temperature history coefficient: set at
0.3 or 1.0 based on heat history in (a) or (b) described below:
[0109] (a) temperature history coefficient=0.3 in a case in which
the ingot is retained at the pre-rolling heating temperature
without cooling the ingot to 320.degree. C. or less in the cooling
step; and
[0110] (b) temperature history coefficient=1.0 in a case in which
the ingot is cooled to a temperature in a range of 320.degree. C.
to room temperature in the cooling step, then heated, and retained
at the pre-rolling heating temperature.
[0111] Mg--Si--Cu-based particles can be easily controlled to have
appropriate particle sizes by retaining the aluminum alloy for not
less than the lower limit of a retention time calculated by the
above-described Equation A. The equation is a mathematical
expression derived by organizing cooling conditions and the amount
of Cu in Al after homogenization treatment on the basis of various
kinds of experimental data.
[0112] In the case of retention at a pre-rolling heating
temperature without cooling from a temperature after homogenization
treatment to 320.degree. C. or less, growth of already precipitated
Mg--Si--Cu-based particles is promoted compared with the new
precipitation of Mg--Si--Cu-based particles, and therefore, a short
time for coarsening to appropriate particle sizes is acceptable.
The reason that the heat history coefficient in Equation A is set
at 0.3 is because the above is intended. In contrast, in the case
of temporally performing cooling to a temperature in a range of
320.degree. C. to room temperature and then performing re-heating
to the pre-rolling heating temperature, fine Mg--Si--Cu-based
particles are precipitated in a process in a low-temperature region
in the cooling after the homogenization treatment and in the
process of increasing temperature from room temperature. It is
found that long time is needed until control to appropriate
particle sizes as compared with the case of retention at a
pre-rolling heating temperature without cooling to 320.degree. C.
or less after cooling because it is necessary to coarsen the
precipitates in the present disclosure. The reason that the heat
history coefficient in Equation A is set at 1.0 is because the
above is intended.
[0113] The retention time before hot rolling is not particularly
restricted as long as being not less than the lower limit of a
retention time calculated by Equation A. If the temperature of the
ingot is within the range of the pre-rolling heating temperature,
the lower limit of the retention time may be achieved by addition
of a time for which the ingot is in a furnace, a migration time,
and a waiting time on a hot-rolling table. The upper limit of the
retention time is not particularly restricted, but hot rolling is
performed after retention for 24 hours or less in usual
operation.
[0114] Coarse precipitated particles grown by the retention at the
pre-rolling heating temperature become the nucleation sites of
recrystallization and have the action of promoting the
recrystallization. In the material structure of the alloy
appropriately retained at the pre-rolling heating temperature, when
precipitated particles having a particle diameter of 0.4 .mu.m to
4.0 .mu.m in crystal grains that can be observed with a scanning
electron microscope are extracted, the average particle diameter of
the precipitated particles is preferably 0.6 .mu.m or more, and
more preferably 0.8 .mu.m or more. A reduction in the number of
fine particles constituting obstacles to grain boundary migration
for recrystallization can also promote the recrystallization. Thus,
the total number of precipitated particles having a particle
diameter of 0.04 .mu.m to 0.40 .mu.m in crystal grains that can be
observed with a scanning electron microscope is preferably 1500
particles/100 .mu.m.sup.2 or less.
[0115] Hot rolling is performed according to a conventional and
common method after the homogenization treatment, the cooling, and
the retention in the hot rolling in such a manner as described
above. A temperature for the hot rolling is set at a temperature
within a range of 370.degree. C. to 440.degree. C. The hot-rolling
temperature or a winding temperature described later is the
temperature of a sheet surface or coil-side wall surface of a
workpiece material. Such temperatures can be measured with a
contact type thermometer or a non-contact type thermometer.
[0116] In the step of the hot rolling, it is important to set the
winding temperature after the hot rolling. In the present
disclosure, an appropriate particle distribution is obtained by the
cooling and the retention at the pre-rolling heating temperature
after the homogenization described above, and an ingot with the
action of promoting recrystallization by coarse precipitated
particles and in the state of a small number of fine particles
obstructing grain boundary migration is hot-rolled. Appropriate
setting of the winding temperature of the obtained hot-rolled sheet
allows recrystallization to occur due to self-annealing and can
result in a recrystallized fine structure on which a material
structure for improving ridging resistance is based.
[0117] In the present disclosure, the winding temperature after the
hot rolling is set at 310 to 380.degree. C., and preferably at 325
to 365.degree. C. When the winding temperature is less than
310.degree. C., it is impossible to stably obtain a recrystallized
structure by self-annealing even if an appropriate particle
distribution is obtained before starting the hot rolling. Even if a
recrystallized structure is obtained by self-annealing, a winding
temperature of more than 380.degree. C. results in the coarse
recrystallized grains of the recrystallized structure and therefore
in the deterioration of ridging resistance.
[0118] After the self-annealing after the hot rolling, cold rolling
is performed until a product sheet thickness is achieved. A total
cold rolling reduction from a hot-rolled sheet thickness to the
product sheet thickness is preferably 65% or more, and more
preferably 75% or more. Such cold rolling allows a rolling texture
to be grown, whereby recrystallized grains grow while eroding a
rolling texture constituent in solution treatment following the
cold rolling, and an aluminum alloy rolled material including a
preferred texture can be obtained. The upper limit value of the
total cold rolling reduction is not particularly limited, but is
set at 85% in the present disclosure.
[0119] The aluminum alloy sheet for molding improved particularly
in bendability and ridging resistance can be obtained by further
subjecting the aluminum alloy sheet allowed to have a predetermined
sheet thickness in such a manner as described above to solution
treatment serving as recrystallization treatment. As the conditions
of the solution treatment serving as the recrystallization
treatment, it is preferable to set a material achieving temperature
in a sheet thickness of 1/4 part at 500.degree. C. or more and
590.degree. C. or less and to set a retention time at the material
achieving temperature at no retention to 5 minutes or less, and it
is still more preferable to set a material achieving temperature in
a sheet thickness of 1/4 part at 530.degree. C. or more and
580.degree. C. or less and to set a retention time at the material
achieving temperature at no retention to 1 minute or less.
[0120] In order to impart favorable bake hardenability to the
aluminum alloy sheet produced in such a manner as described above,
it is possible to perform preliminary ageing treatment by which the
aluminum alloy sheet is retained for 1 hour or more in a
temperature range of 50 to 150.degree. C. immediately after the
solution treatment. However, the preliminary ageing treatment does
not essentially influence the texture. Thus, whether or not
preliminary ageing treatment is performed is not an essential
requirement in the present disclosure aimed at improvement of
ridging resistance influenced by a material structure.
EXAMPLES
[0121] More specific examples of the aluminum alloy rolled material
for molding according to the present disclosure will now be
described. In the examples, plural aluminum alloy rolled sheet
materials for molding with different compositions were produced
while adjusting production conditions. The mechanical properties
and textures of the produced aluminum alloy rolled sheet materials
were measured and evaluated, and tests for evaluating the
mechanical characteristics (tensile strength and 0.2% proof
stress), bending workability, and ridging resistance of the
aluminum alloy rolled sheet materials were conducted.
[0122] (i) Production of Aluminum Alloy Rolled Sheet Material
[0123] First, the ingots of aluminum alloys with compositions shown
in Table 1 were made by DC casting. The obtained ingot (lateral
cross-section dimensions: thickness of 500 mm, width of 1000 mm)
was subjected to homogenization treatment at 550.degree. C. for 6
hours, then subjected to a cooling step, retained at a pre-rolling
heating temperature, and then subjected to hot rolling. In the
present examples, the pre-rolling heating temperature and a
hot-rolling temperature were set at the same temperature. As heat
histories between the cooling and the hot rolling after the
homogenization treatment, two patterns of a case in which after the
homogenization treatment, the ingot was cooled to the pre-rolling
heating temperature and retained at the pre-rolling heating
temperature without being allowed to be at 320.degree. C. or less
(direct retention), and a case in which the ingot after the
homogenization treatment was cooled to room temperature, re-heated
to the pre-rolling heating temperature, and retained at the
pre-rolling heating temperature (re-heating) were performed. The
cooling rates, the heat histories, and the pre-rolling heating
temperatures in the present examples are shown in Table 2. The
cooling rate of 1/4 part of the ingot was measured using a dummy
slab in which a thermocouple was embedded, and which had the same
size. The ingot was retained at the pre-rolling heating temperature
with reference to the needed retention time calculated from the
Equation A described above depending on the heat histories.
[0124] Then, the hot rolling was performed. A temperature at which
the hot-rolled sheet after the hot rolling was wound was adjusted
as shown in Table 2. After the hot rolling, cold rolling and
solution treatment were performed. A rolling reduction in the cold
rolling was shown in Table 2. In the solution treatment, solution
treatment was performed in a continuous annealing furnace on
conditions of 550.degree. C. and 1 minute, and preliminary ageing
treatment was performed at 80.degree. C. for 5 hours immediately
after forced-air cooling with a fan to around room temperature. The
aluminum alloy rolled sheet materials according to disclosure
examples and comparative examples were produced by the above
steps.
[0125] In the present examples, the state of the distribution of
Mg--Si--Cu-based particles in the aluminum alloy ingot before the
hot rolling was also examined. In the examination, a small piece
sample was cut from a thickness of 1/4 part in the center of the
width of the ingot at a position of 500 mm from an end of the ingot
after the casting of the above-described test material. Samples of
which the heat histories (heat histories from homogenization
treatment to retention at the hot rolling temperature before hot
rolling) equivalent to those of the disclosure examples and the
comparative examples in Table 2 were reproduced in a laboratory
were generated, mirror-polishing of surfaces of the samples was
performed, and the images of the surfaces were then taken with
FE-SEM and subjected to image analysis. In the evaluation of the
material structures, precipitated particles having a particle
diameter of 0.4 .mu.m to 4.0 .mu.m in crystal grains that were able
to be observed in the SEM images were extracted, and the average
particle diameter of the particles was calculated. In addition, the
number of precipitated particles having a particle diameter of 0.04
.mu.m to 0.40 .mu.m in the crystal grains that were able to be
observed in the SEM images was quantified. The results are also
shown in Table 2.
[0126] Further, the state of recrystallization after the hot
rolling was confirmed. In a method of the confirmation, the three
outer windings of the hot-rolled sheet were removed, and a sample
was then collected from the center in a width direction. The
crystal grain structures of cross sections parallel in a rolling
direction were photographed, and visual determination was performed
whether recrystallization occurred at 100 lattice points obtained
by drawing 10 evenly spaced straight lines in a visual field of 2
mm.times.4 mm in longitudinal and lateral directions, respectively.
The number of lattice points corresponding to recrystallized grains
was defined as a recrystallization rate, and a case in which the
recrystallization rate was 95% or more was defined as generation of
a recrystallized structure.
TABLE-US-00001 TABLE 1 Chemical component (mass %) Alloy Si Fe Cu
Mn Mg Cr Zn Ti Al AA A 0.74 0.16 0.68 0.12 0.68 0.02 0.03 0.02 Bal.
6111 B 0.71 0.17 0.22 0.08 0.70 0.01 0.15 0.03 Bal. 6061 C 0.68
0.10 0.32 0.14 0.72 0.01 0.17 0.01 Bal. 6061 D 0.73 0.18 1.40 0.09
0.70 0.04 0.10 0.02 Bal. -- E 0.69 0.17 1.61 0.11 0.68 0.02 0.08
0.04 Bal. -- F 0.27 0.13 0.72 0.14 0.73 0.03 0.23 -- Bal. -- G 0.34
0.20 0.79 0.12 0.76 0.02 0.26 0.09 Bal. -- H 1.41 0.13 0.69 0.01
0.70 -- 0.16 0.02 Bal. 6110 I 1.61 0.16 0.67 0.13 0.70 0.01 0.21
0.02 Bal. -- J 0.71 0.02 0.70 0.06 0.26 0.01 0.19 0.03 Bal. -- K
0.77 0.02 0.78 0.01 0.33 0.03 0.33 0.03 Bal. -- L 0.72 0.02 0.67
0.04 1.42 -- 0.09 0.02 Bal. -- M 0.67 0.18 0.68 0.09 1.63 0.02 0.11
0.06 Bal. -- N 0.74 0.01 0.54 0.02 0.49 -- -- 0.01 Bal. -- O 0.65
0.08 0.63 0.43 0.61 0.01 0.01 0.02 Bal. -- P 0.69 0.15 0.63 0.55
0.64 0.03 0.02 0.02 Bal. -- Q 0.66 0.06 0.64 0.02 0.63 0.35 0.01
0.02 Bal. -- R 0.72 0.17 0.68 0.11 0.62 0.43 0.01 0.03 Bal. -- S
0.69 0.37 0.70 0.11 0.64 0.01 0.01 0.02 Bal. -- T 0.70 0.45 0.69
0.08 0.64 0.01 0.01 0.02 Bal. -- The mark "--" shows that a content
was not more than a detection limit.
TABLE-US-00002 TABLE 2 Precipitate of ingot before Retention
conditions at pre-rolling hot rolling Cooling heating temperature
Average rate after Time (h) Actual particle Production
homogenization Heat Temperature calculated by performance diameter
process Alloy (.degree. C./h) history*.sup.1 (.degree. C.)*.sup.2
Equation A time (h) (.mu.m) 1 A 90 Re- 400 2.91 4.0 0.9 heating 2 B
90 Re- 400 0.94 2.0 1.2 heating 3 C 90 Re- 400 1.37 2.0 0.8 heating
4 D 90 Re- 400 6.00 8.0 1.4 heating 5 E 90 Re- 400 6.90 8.0 1.0
heating 6 F 90 Re- 400 3.09 4.0 0.8 heating 7 G 90 Re- 400 3.39 4.0
0.9 heating 8 H 90 Re- 400 2.96 4.0 1.2 heating 9 I 90 Re- 400 2.87
4.0 1.0 heating 10 J 90 Re- 400 3.00 4.0 0.9 heating 11 K 90 Re-
400 3.34 4.0 0.8 heating 12 L 90 Re- 400 2.87 4.0 1.1 heating 13 M
90 Re- 400 2.91 4.0 1.0 heating 14 N 90 Re- 400 2.31 4.0 1.0
heating 15 O 90 Re- 400 2.70 4.0 1.1 heating 16 P 90 Re- 400 2.70
4.0 1.2 heating 17 Q 90 Re- 400 2.74 4.0 0.9 heating 18 R 90 Re-
400 2.91 4.0 1.0 heating 19 S 90 Re- 400 3.00 4.0 1.2 heating 20 T
90 Re- 400 2.96 4.0 1.3 heating 21 A 1800 Direct 440 3.91 4.0 1.3
retention 22 A 90 Direct 400 0.87 1.0 1.2 retention 23 A 30 Direct
370 0.50 1.0 1.0 retention 24 A 90 Re- 450 2.91 4.0 1.9 heating 25
A 1800 Re- 440 13.03 15.0 1.4 heating 26 A 300 Re- 400 5.32 6.0 1.1
heating 27 A 90 Re- 370 2.91 4.0 0.7 heating 28 A 90 Re- 360 2.91
4.0 0.3 heating 29 A 90 Re- 400 2.91 1.0 0.4 heating 30 A 90 Re-
400 2.91 4.0 0.9 heating 31 A 90 Re- 400 2.91 4.0 0.9 heating 32 A
90 Re- 400 2.91 4.0 0.9 heating 33 A 90 Re- 400 2.91 4.0 0.9
heating 34 A 90 Re- 400 2.91 4.0 0.9 heating Precipitate of ingot
before hot rolling Cold Number Hot-rolling Recrystal- Inter rolling
Production (particles/ winding lization mediate reduction process
100 .mu.m.sup.2) temperature (.degree. C.) rate annealing (%)
Classification 1 788 346 100% No 80 Disclosure Example 2 512 311
100% No 80 Comparative Example 3 1284 358 100% No 80 Disclosure
Example 4 859 326 100% No 80 Disclosure Example 5 779 351 100% No
80 Comparative Example 6 462 338 100% No 80 Comparative Example 7
1411 374 100% No 80 Disclosure Example 8 982 312 100% No 80
Disclosure Example 9 783 324 100% No 80 Comparative Example 10 884
347 100% No 80 Comparative Example 11 1366 359 100% No 80
Disclosure Example 12 687 326 100% No 80 Disclosure Example 13 769
341 100% No 80 Comparative Example 14 689 323 100% No 80 Disclosure
Example 15 901 362 100% No 80 Disclosure Example 16 992 371 100% No
80 Comparative Example 17 1013 361 100% No 80 Disclosure Example 18
1097 378 100% No 80 Comparative Examples 19 863 356 100% No 80
Disclosure Example 20 928 347 100% No 80 Comparative Example 21 402
339 100% No 70 Disclosure Example 22 532 337 100% No 80 Disclosure
Example 23 746 351 100% No 70 Disclosure Example 24 322 352 100% No
70 Comparative Example 25 681 341 100% No 80 Disclosure Example 26
844 356 100% No 80 Disclosure Example 27 1003 326 100% No 80
Disclosure Example 28 2133 321 46% No 80 Comparative Example 29
1724 339 18% No 70 Comparative Example 30 788 388 100% No 70
Comparative Example 31 788 305 54% No 70 Comparative Example 32 788
268 0% Batch 70 Comparative annealing Example immediately after hot
rolling 33 788 291 0% 30% cold 70 Comparative rolling + Example
batch annealing 34 788 237 0% 30% cold 70 Comparative rolling +
Example CAL *.sup.1"Heat history" means a heat history from cooling
after homogenization treatment to retention at a pre-rolling
heating temperature. "Direct retention": An ingot was cooled to a
pre-rolling heating temperature so as to be prevented from being
cooled to 320.degree. C. or less, and was retained. "Re-heating":
An ingot was cooled to room temperature, then re-heated, and
retained at a pre-rolling heating temperature. *.sup.2Pre-rolling
heating temperature, which was set at the same temperature as a
hot-rolling temperature in the present embodiment.
[0127] (ii) Mechanical Properties of Aluminum Alloy Rolled Sheet
Material, and Measurement and Evaluation of Texture
[0128] For each aluminum alloy sheet material produced in the
present examples, a JIS No. 5 test piece was first cut in a
direction parallel to a rolling direction, and the tensile strength
(ASTS) and 0.2% proof stress (ASYS) of the test piece were measured
by a tensile test.
[0129] The states (cube orientation density, and dispersion of
average Taylor factors) of the texture of a predetermined plane,
defined in the present disclosure, of each sheet material were
measured. For the cube orientation density, a plane S2 at a depth
of 1/4 of a total sheet thickness was exposed by mechanical
polishing and subjected to X-ray diffraction measurement, the
orientation information of the texture was acquired by measuring
the incomplete pole figures of a (111) plane, a (220) plane, and a
(200) plane, and the cube orientation density was calculated using
pole figure analysis software, as described above.
[0130] Further, a plane S3 at a depth of 1/2 of a total sheet
thickness was exposed by mechanical polishing, and SEM-EBSD
measurement of the exposed plane was performed by the
above-described method, as described above. An area SA was set in
the center in a sheet width direction as a representative example
of an arbitrary area in the S3 plane, and the orientation
information of the textures of corresponding subareas SA1, SA2, . .
. , SA10 in the area SA was then acquired. Average Taylor factors
were calculated from the obtained orientation information by the
above-described method, and the absolute value of the difference
between the maximum value and the minimum value of the average
Taylor factors between the corresponding subareas in the same plane
was calculated.
[0131] (iii) Evaluation of Workability and Ridging Resistance of
Aluminum Alloy Rolled Sheet Material
[0132] The workability and ridging resistance of each aluminum
alloy sheet material produced in the present examples were
evaluated to examine production conditions and the relationships of
the configuration of the alloy sheet material, workability, and the
like. First, the ridging resistance was evaluated using a
conventionally performed simple evaluation technique. Specifically,
JIS No. 5 test pieces were collected along a direction at
90.degree. with respect to a rolling direction and subjected to 10%
and 15% stretches, respectively. Assuming that a stripe pattern
(stripe-shaped recessed and projected pattern) generated on a
surface along the rolling direction was regarded as a ridging mark,
the presence or absence and degree of generation of the stripe
pattern were determined by visual observation. The results are
shown in Table 3. In Table 3, "Excellent" shows the absence of a
stripe pattern, "Good" shows a state in which a slight stripe
pattern was visually observed, "Fair" shows a moderate stripe
pattern, and "Poor" shows a state in which a stripe pattern was
vivid. In the present embodiment, it was determined that
"Excellent" or "Good" showed that ridging resistance was
favorable.
[0133] In addition, bending workability was evaluated by a
180-degree bending test. Bending test pieces were collected along a
direction at 90.degree. with respect to the rolling direction and
subjected to 5% predistortion. Then, the 180-degree bending test of
the bending test pieces between which an intermediate plate having
a thickness of 1 mm (bend radius: 0.5 mm) was interposed was
conducted. The bending workability of the appearance of the bend in
each direction was given a point (score) in comparison with the
bending workability evaluation samples illustrated in FIG. 2. The
results are shown in Table 3. The higher numerical value of the
score in the bending test represents more favorable bending
workability. In the present embodiment, it was determined that a
point of "6" or more showed favorable bending workability, a point
of "7" or more showed high grade bending workability, and a point
of "8" or more showed very high grade bending workability.
TABLE-US-00003 TABLE 3 States of Evaluation of texture ridging
Tensile test Disper- resisteance results Cube sion of After After
Bending ASTS - Production orientation Taylor 10% 15% test ASYS ASTS
ASYS Classifi- process Alloy density factors stretch stretch score
(MPa) (MPa) (MPa) cation 1 A 12 0.7 Excel- Excel- 8 116 245 129
Disclosure lent lent Example 2 B 26 0.6 Excel- Excel- 9 105 219 114
Comparative lent lent Example 3 C 18 0.8 Excel- Excel- 8 108 229
121 Disclosure lent lent Example 4 D 10 0.7 Excel- Excel- 7 140 269
129 Disclosure lent lent Example 5 E 13 0.6 Excel- Excel- 5 142 268
126 Comparative lent lent Example 6 F 21 0.7 Excel- Excel 8 101 199
98 Comparative lent lent Example 7 G 12 0.7 Excel- Excel- 8 110 233
123 Disclosure lent lent Example 8 H 15 0.6 Excel- Excel- 7 138 261
123 Disclosure lent lent Example 9 I 13 0.7 Excel- Excel- 5 139 266
127 Comparative lent lent Example 10 J 20 0.7 Excel- Excel- 8 100
197 97 Comparative lent lent Example 11 K 16 0.7 Excel- Excel- 8
103 225 122 Disclosure lent lent Example 12 L 12 0.7 Excel- Excel-
7 138 269 131 Disclosure lent lent Example 13 M 11 0.7 Excel-
Excel- 5 140 268 128 Comparative lent lent Example 14 N 13 0.8
Excel- Excel- 6 106 228 122 Disclosure lent lent Example 15 O 11
1.0 Good Good 7 110 231 121 Disclosure Example 16 P 11 1.0 Good
Good 5 112 234 122 Comparative Example 17 Q 13 1.0 Good Good 7 109
232 123 Disclosure Example 18 R 12 1.0 Good Good 5 113 237 124
Comparative Example 19 S 14 0.7 Excel- Excel- 6 111 233 122
Disclosure lent lent Example 20 T 10 0.6 Excel- Excel- 5 112 236
124 Comparative lent lent Example 21 A 15 0.5 Excel- Excel- 9 110
241 131 Disclosure lent lent Example 22 A 15 0.6 Excel- Excel- 8
115 243 128 Disclosure lent lent Example 23 A 15 0.7 Excel- Excel-
8 112 239 127 Disclosure lent lent Example 24 A 11 1.2 Fair Fair 8
109 233 124 Comparative Example 25 A 13 0.7 Excel- Excel- 8 120 252
132 Disclosure lent lent Example 26 A 12 0.6 Excel- Excel- 9 121
254 133 Disclosure lent lent Example 27 A 12 0.8 Excel- Excel- 8
119 249 130 Disclosure lent lent Example 28 A 12 1.6 Poor Poor 9
121 247 126 Comparative Example 29 A 20 1.6 Poor Poor 9 122 249 127
Comparative Example 30 A 18 1.5 Fair Fair 9 115 245 130 Comparative
Example 31 A 20 1.6 Poor Poor 9 116 246 130 Comparative Example 32
A 23 1.8 Poor Poor 9 113 237 124 Comparative Example 33 A 21 1.6
Fair Fair 8 112 235 123 Comparative Example 34 A 4 0.1 Excel-
Excel- 5 129 252 123 Comparative lent lent Example
[0134] The constituent compositions of all of the aluminum alloy
sheet materials of the production processes No. 1, No. 3, No. 4,
No. 7, No. 8, No. 11, No. 12, No. 14, No. 15, No. 17, No. 19, Nos.
21 to 23, and Nos. 25 to 27 which are the disclosure examples of
the present disclosure are within the ranges defined in the present
disclosure. In addition, a cube orientation density in a plane S2
and the dispersion of average Taylor factors in a plane S3 satisfy
the conditions defined in the present disclosure. The aluminum
alloy sheets were confirmed to have favorable ridging resistance
and favorable bending workability.
[0135] In contrast, the constituent compositions of the aluminum
alloy sheet materials of the production processes No. 2, No. 6, and
No. 10 corresponding to the comparative examples are outside the
ranges defined in the present disclosure. The results of the
aluminum alloy sheet materials comprising an alloy B (No. 2) having
a Cu content of less than 0.3%, an alloy F (No. 6) having a Si
content of less than 0.3%, and an alloy J (No. 10) having a Mg
content of less than 0.3% are shown. In the aluminum alloy sheets,
a difference between a tensile strength (ASTS) and a 0.2% proof
stress (ASYS) is less than 120 MPa because the contents of Cu, Si,
and Mg associated with mechanical characteristics are less than the
amounts defined in the present disclosure.
[0136] The constituent compositions of the aluminum alloy sheet
materials of the production processes No. 5, No. 9, and No. 13 are
also outside the ranges defined in the present disclosure. The
results of the aluminum alloy sheet materials comprising an alloy E
(No. 5) having a Cu content of more than 1.5%, an alloy I (No. 9)
having a Si content of more than 1.5%, and an alloy M (No. 13)
having a Mg content of more than 1.5% are shown. Because the
contents of Cu, Si, and Mg in the aluminum alloy sheet materials
are more than the ranges defined in the present disclosure, coarse
particles formed in the production steps also remain in the product
sheets and become the origins of cracks in bending working, and
therefore, the aluminum alloy sheet materials do not have
sufficient bending workability. Scores in the bending test were low
in the comparative examples.
[0137] The contents of Mn, Cr, and Fe in the aluminum alloy sheet
materials of the production processes Nos. 16, 18, and 20 are more
than the preferred ranges. In the bending test, the aluminum alloy
sheet materials had low scores, which were results in which it was
necessary to regard the aluminum alloy sheet materials as
comparative examples.
[0138] Although the ridging resistance and bending workability of
the aluminum alloy sheet of the production process No. 14 were
acceptable, the contents of Fe, Mn, and Cr in the aluminum alloy
sheet were less than the preferred lower limit values (Mn: 0.03% or
less, Cr: 0.01% or less, and Fe: 0.03% or less). Therefore, slight
surface roughening which can be considered to be caused by
coarsening of crystal grains in solution treatment occurred in the
aluminum alloy sheet. Thus, the workability of the alloy may be
considered to be acceptable to some extent, but the alloy can be
considered not to be recommended when importance is particularly
placed on working quality.
[0139] The constituent compositions of the aluminum alloy sheets of
the production processes No. 24 and Nos. 28 to 34 corresponding to
the comparative examples are within the ranges defined in the
present disclosure. However, the cube orientation densities and
dispersions of average Taylor factors of the final sheets are
outside the ranges defined in the present disclosure due to the
production process conditions. As a result, the aluminum alloy
sheets are inferior in ridging resistance and bending
workability.
[0140] These comparative examples will be specifically described.
First, Table 2 reveals that the pre-rolling heating temperature in
the production process No. 28 is lower than the preferred
condition. In this comparative example, retention was performed at
the hot rolling temperature for not less than the needed time
calculated by Equation A before hot rolling, but any precipitate
having a size sufficient for promoting self-annealing was not able
to be obtained, and recrystallization after the hot rolling did not
sufficiently proceed. In the production process No. 29, the
retention time at the pre-rolling heating temperature was shorter
than the needed time calculated by Equation A. Therefore, a large
number of fine precipitates were formed. As a result, the
recrystallization after the hot rolling did not sufficiently
proceed. Further, in the production process No. 31, the temperature
at which a hot-rolled sheet after hot rolling was wound was less
than 310.degree. C., and therefore, recrystallization due to
self-annealing did not proceed. The aluminum alloy sheet materials
of No. 28, No. 29, and No. 31 are aluminum alloy sheet materials
with insufficient recrystallization in states after hot-rolling
winding. Table 3 reveals that the differences between the maximum
values and the minimum values of the average Taylor factors of the
planes S3 of the final sheets of the aluminum alloy sheet materials
of No. 28, No. 29, and No. 31 were more than 1.0, and the aluminum
alloy sheet materials were inferior in ridging resistance.
[0141] The aluminum alloy sheet material in the production process
No. 24 was produced at a pre-rolling heating temperature set at
more than 440.degree. C., and the aluminum alloy sheet material in
the production process No. 30 was produced at a winding temperature
of more than 380.degree. C. after hot rolling. The textures of the
aluminum alloy sheet materials were insufficient controlled, the
differences between the maximum values and the minimum values of
the average Taylor factors of the planes S3 of the final sheets of
the aluminum alloy sheet materials were more than 1.0, and the
aluminum alloy sheet materials were inferior in ridging
resistance.
[0142] The production processes Nos. 32 to 34 are production
examples in which intermediate annealing was performed after hot
rolling while setting a temperature at which a hot-rolled sheet
after the hot rolling was wound at less than 310.degree. C. These
results reveal that it is particularly important to manage cooling
after homogenization treatment, retention at a pre-rolling heating
temperature, and a temperature at which a hot-rolled sheet after
hot rolling is wound, for improving bending workability and ridging
resistance in a good balance. In addition, it is found that when
treatment outside the ranges of the preferred conditions is
performed in these processes, it is difficult to attain an
objective, and intermediate annealing is also ineffective. The low
effect of the intermediate annealing is understood from inferior
ridging resistance in intermediate annealing (batch annealing at
360.degree. C. for 120 minutes) after hot rolling like No. 32. Like
No. 33, even when cold rolling (30%) was performed before
intermediate annealing (batch annealing at 360.degree. C. for 120
minutes), only ridging resistance was improved. In No. 34,
intermediate annealing (at 500.degree. C. or more for 1 minute or
less) was performed in a continuous annealing furnace, and a cube
orientation density was outside the definition and bending
workability was deteriorated although the dispersion of the Average
Taylor factors of the plane S3 was favorable and ridging resistance
was improved. As described above, the performance of intermediate
annealing enables a texture to be changed depending on the
conditions of the intermediate annealing, but is incapable of
allowing both of the cube orientation density of a final sheet and
the dispersion of the average Taylor factors of a plane S3 to fall
within preferred ranges.
INDUSTRIAL APPLICABILITY
[0143] As described above, the aluminum alloy rolled material
according to the present disclosure is an aluminum alloy rolled
material that is based on an Al--Mg--Si-based alloy and is allowed
to have compatibility among press formability, ridging resistance,
and bending workability by allowing the mechanical properties and
texture of the aluminum alloy rolled material to be appropriate in
consideration of the content of Cu. The present disclosure can also
be utilized for molding-worked components such as the panels and
chassis of electronic and electrical instruments and the like as
well as automotive applications such as automotive body sheets
applied to the body panels of automobiles.
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