U.S. patent application number 15/574710 was filed with the patent office on 2018-05-31 for high-strength hot-forged aluminum alloy.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). The applicant listed for this patent is Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Masayuki HORI, Yoshiya INAGAKI, Hisao SHISHIDO.
Application Number | 20180148815 15/574710 |
Document ID | / |
Family ID | 57545680 |
Filed Date | 2018-05-31 |
United States Patent
Application |
20180148815 |
Kind Code |
A1 |
SHISHIDO; Hisao ; et
al. |
May 31, 2018 |
HIGH-STRENGTH HOT-FORGED ALUMINUM ALLOY
Abstract
In the microstructure of a hot-forged 6000-series aluminum alloy
having a specific chemical composition, grains including small
grains with a misorientation of 2.degree. or more are refined, and
a KAM, which is an average misorientation of the grains, is
controlled within a specific range. This allows the hot-forged
6000-series aluminum alloy to have excellent stress corrosion
cracking resistance and still have high tensile strength, high
yield strength, and high elongation.
Inventors: |
SHISHIDO; Hisao; (Kobe-shi,
JP) ; INAGAKI; Yoshiya; (Inabe-shi, JP) ;
HORI; Masayuki; (Inabe-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) |
Kobe-shi |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Kobe-shi
JP
|
Family ID: |
57545680 |
Appl. No.: |
15/574710 |
Filed: |
June 8, 2016 |
PCT Filed: |
June 8, 2016 |
PCT NO: |
PCT/JP2016/067071 |
371 Date: |
November 16, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C 21/02 20130101;
C22C 21/08 20130101; C22F 1/002 20130101; C22C 21/06 20130101; C22F
1/05 20130101 |
International
Class: |
C22F 1/05 20060101
C22F001/05; C22F 1/00 20060101 C22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2015 |
JP |
2015-121043 |
Claims
1. A high-strength hot-forged aluminum alloy comprising, in mass
percent: Si in a content of 0.7% to 1.5%; Mg in a content of 0.6%
to 1.2%; Fe in a content of 0.01% to 0.5%; at least one element
selected from the group consisting of: Mn in a content, of 0.05% to
0.8%, Cr in a content of 0.01% to 0.5%, and Zr in a content of
0.01% to 0.2%; and wherein, in a microstructure in a thickness
central part of the hot-forged aluminum alloy as measured by
SEM-EBSD analysis, grains with a misorientation of 2.degree. or
more have an average grain size of 30 .mu.m or less, and grains
have a KAM of from 0.6.degree. to 2.0.degree., where the KAN is an
average misorientation of the grains.
2. The high-strength hot-forged aluminum alloy according to claim
1, further comprising, in mass percent, at least one element
selected from the group consisting of: Cu in a content of 0.05% to
1.0%; Ti in a content of 0.01% to 0.1%; and Zn in a content of
0.005% to 0.2%.
3. The high-strength hot-forged aluminum alloy according to claim
1, wherein the hot-forged aluminum alloy has a tensile strength of
420 MPa or more, a 0.2% yield strength of 400 MPa or more, and an
elongation of 12% or more.
4. The high-strength hot-forged aluminum alloy according to claim
2, wherein the hot-forged aluminum alloy has a tensile strength of
420 MPa or more, a 0.2% yield strength of 400 MPa or more, and an
elongation of 12% or more.
Description
TECHNICAL FIELD
[0001] The present invention relates to high-strength, hot-forged
aluminum alloys. Hereinafter "aluminum" is also simply referred to
as "Al".
BACKGROUND ART
[0002] Reduction in body weight of, and resulting improvements in
fuel efficiency of automobiles and other transports have been
pursued so as, to cope with global environmental issues caused
typically by exhaust gases. To this end, 6000-series (Al--Mg--Si)
hot-forged aluminum alloys as prescribed in Aluminum Association
(AA) standards or Japanese Industrial Standards (JIS) are used for
structural components and structural parts of automobiles and other
transports and, in particular, for automobile suspension parts such
as upper arms and lower arms. Hot-forged 6000-series aluminum
alloys, when used for these structural components and structural
parts, offer high strength and high toughness and have relatively
excellent corrosion resistances. Hereinafter, such structural
components and structural parts of transports will be illustrated
by taking automobile suspension parts as an example.
[0003] For further weight reduction of automobiles, automobile
suspension parts require higher strength and higher toughness, in
addition to smaller thicknesses. The automobile suspension parts
also function as safety-related parts and require higher corrosion
resistance to intergranular corrosion (grain-boundary corrosion)
and to stress corrosion cracking so as to ensure reliability as the
safety-related parts. Accordingly, various techniques have been
developed to improve chemical compositions and microstructures of
material hot-forged 6000-series aluminum alloys.
[0004] For example, in well known techniques, transition elements
having grain refinement effects, such as Mn, Zr, and Cr, are added,
or hot forging is performed at a relatively high temperature of
about 450.degree. C. to about 570.degree. C., for the grain
refinement of forged 6000-series aluminum alloys. In a proposed
technique to provide high strength and high toughness, an ingot is
once hot-extruded into an extrusion (extruded material), and the
extrusion is used and subjected as a material to hot forging into a
forged material so as to refine an unrecrystallized region in the
microstructure of the forged material (see Patent Literature (PTL)
1).
[0005] In contrast, though not in the field of hot-forged
materials, metallurgical techniques have been proposed so as to
offer higher strength of aluminum alloy materials (see PTL 2 and
PTL 3). With these techniques, a 6000-series aluminum alloy ingot
is sequentially subjected to solution treatment (solution heat
treatment), repeatedly to warm forging at about 150.degree. C. to
about 250.degree. C. and to artificial aging.
[0006] Also not in the field of aluminum alloys, but in the field
of rolled sheets of Corson alloys (Cu--Ni--Si copper alloys), there
have been proposed Corson alloys having small anisotropy m
strength, having a high yield strength particularly in a direction
perpendicular to the sheet rolling direction, and offering
bendability in good balance (see (PTL 4 and PTL 5). In these Corson
alloys, a kernel average misorientation (KAM) is controlled, where
the KAM is an average misorientation of grains and is determined by
SEM-EBSD analysis.
[0007] The KAM is also publicly known typically in the field of
steel sheets as an index for good balance among strength,
elongation, and stretch flangeability of high-strength
(high-tensile) cold-rolled steel sheets (see PTL 6).
CITATION LIST
Patent Literature
[0008] PTL 1: Japanese Unexamined Patent Application Publication
(JP-A) No. 2011-225988 [0009] PTL 2: JP-A No. 2014-218685 [0010]
PTL 3: Japanese Patent. No. 5082483 [0011] PTL 4: Japanese Patent
No. 5314663 [0012] PTL 5: Japanese Patent No. 5476149 [0013] PTL 6:
Japanese Patent No. 4977184
DISCLOSURE OF INVENTION
Technical Problem
[0014] When an extrusion (extruded material) is used as a material
for hot forging as in the technique disclosed in PLT 1, the
resulting hot-forged material has a high yield strength in a
direction parallel to the extrusion direction, but
disadvantageously has high anisotropy in strength.
[0015] The grain refinement techniques in the conventional
hot-forged 6000-series aluminum alloys are still susceptible to
improvements, so as to offer higher tensile strength and higher
yield strength.
[0016] The techniques of repeatedly performing warm forging on
6000-series aluminum alloy ingots and then performing artificial
aging to offer higher strength as proposed in PTL 2 and PTL 3 have
been believed to less effectively offer higher strength if hot
forging at a higher temperature typically of 500.degree. C. is
performed instead of the warm forging. Thus, it is still unknown
that these techniques are effective for better mechanical
properties of hot-forged 6000-series aluminum alloys.
[0017] It is also unknown that the control of the KAM, which is an
average misorientation of gains, is effective for better mechanical
properties of hot-forged 6000-series aluminum alloys, even if the
KAM control is effective for better mechanical properties of rolled
sheets of copper alloys or steels as in PLT 3 to 6. This is because
the hot-forged 6000-series aluminum alloys are significantly
different from these rolled sheets in alloy chemical composition,
properties, and production method.
[0018] The present invention has been made while focusing on these
circumstances and has an object to provide a hot-forged 6000-series
aluminum alloy that has excellent corrosion resistance and still
has high tensile strength, high yield strength, and high
elongation.
Solution to Problem
[0019] To achieve the object, the present invention provides a
hot-forged aluminum alloy containing, in mass percent, Si in a
content of 0.7% to 1.5%, Mg in a content of 0.6% to 1.2%, Fe in a
content of 0.01% to 0.5%, and at least one element selected from
the group consisting of Mn in a content of 0.05% to 0.8%, Cr in a
content of 0.01% to 0.5%, and Zr in a content of 0.01% to 0.2%,
with the remainder consisting of Al and unavoidable impurities. In
a microstructure in a thickness cent-al part of the hot-forged
aluminum alloy, as measured by SEM-EBSD analysis, grains with a
misorientation of 2.degree. or more have an average grain size of
30 .mu.m or less, and the grains have a KAM of from 0.6.degree. to
2.0.degree., where the KAM is an average misorientation of the
grains.
Advantageous Effects of Invention
[0020] The inventors of the present invention have newly found that
not only the grain refinement of a hot-forged 6000-series aluminum
alloy, but also the KAM, which results from quantifying the average
misorientation of grains, have a strong correlation with the
tensile strength and yield strength of this forged material.
[0021] The KAM itself represents the quantity of average
misorientation of grains measured by SEM-EBSD analysis, and the
technique using the KAM is publicly known also as a calculation
technique for grain residual strain in other fields than hot-forged
6000-series aluminum alloys, as described in PTL 3 to 6.
[0022] The KAM can be advantageously controlled by further
subjecting a forged material produced through hot forging to
relatively mild forging in a cold to warm region and subsequent
artificial aging repeatedly, without changing an
already-standardized 6000-sees aluminum alloy chemical composition
of the forged material.
[0023] The present invention can provide a hot-forged 6000-series
aluminum alloy which has high tensile strength, high yield
strength, and high elongation without deterioration in corrosion
resistance, by refinement of the grains with a misorientation of
2.degree. or more and the control of the KAM. This allows the
hot-forged 6000-series aluminum alloy to offer better reliability
as a safety-related part in automobile suspension parts.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1A is a side view of a test specimen for stress
corrosion cracking resistance evaluation, used in experimental
examples; and
[0025] FIG. 1B is a plan view of the a test specimen for stress
corrosion cracking instance evaluation, used in the experimental
examples.
DESCRIPTION OF EMBODIMENTS
[0026] Some embodiments of the present invention will be
illustrated specifically below.
[0027] Chemical Composition
[0028] Initially, the chemical composition of an aluminum alloy
will be illustrated below, where the aluminum alloy constitutes the
hot-forged aluminum alloy (hereinafter also simply referred to as a
"hot-forged material" or "forged material") according to the
present invention and constitutes an ingot as a material for the
forged material.
[0029] The chemical composition of the 6000-series
(Al--Mg--Si-series) aluminum alloy for use in the present invention
should be determined or specified so as to ensure high strength and
high corrosion resistance or durability, typified by stress
corrosion cracking resistance, required when the resulting
hot-forged aluminum alloy is to be used typically as the forged
suspension parts. Accordingly, of chemical compositions within the
ranges of 6000-series aluminum alloys, the aluminum alloy for use
in the present invention has a chemical composition including, in
mass percent, Si in a content of 0.7% to 1.5%, Mg in a content of
0.6% to 1.2%, Fe in a content of am % to 0.5%, and at least one
element selected from the group consisting of Mn in a content of
0.05% to 0.8%, Cr in a content of 0.01% to 0.5%, and Zr in a
content of 0.01% to 0.2%, with the reminder consisting of Al and
unavoidable impurities.
[0030] For better properties such as higher strength, the aluminum
alloy may thither contain, in mass percent, at least one element
selected from the group consisting of Cu in a content of 0.05% to
1.0%, Ti in a content of 0.01% to 0.1%, and Zn in a content of
0.005% to 0.2%. All percentages in contents of elements are mass
percent.
[0031] Other impurity elements, which are inevitably included into
the aluminum alloy typically from scrap as a melting material, are
allowed to be contained as the unavoidable impurities of the
remainder in the chemical composition, in common amounts on the
basis typically of the upper limits prescribed in JIS. Next,
critical significance and preferred ranges of contents of the
elements will be described.
[0032] Si: 0.7% to 1.5%
[0033] Silicon (Si) precipitates, with Mg, mainly as a needle-like
.beta.' phase in grains upon artificial aging and is necessary for
offering high strength and high yield strength upon use of the
hot-forged aluminum alloy as an automobile suspension part.
[0034] Si, if present in an excessively low content, may
precipitate in an excessively small amount upon artificial aging
and may fail to offer high strength.
[0035] In contrast, Si, if present in an excessively high content,
may cause coarse particles of elementary Si to form and precipitate
upon casting and in the course of quenching after solution
treatment and may thereby cause the hot-forged aluminum alloy to
have lower corrosion resistance and lower toughness. In addition,
such a large amount of excessive Si may impede the hot-forged
aluminum alloy from having high corrosion resistance, high
toughness, and high fatigue properties; and may also adversely
affect hot forgeability and workability and may cause deterioration
typically in elongation.
[0036] For these reasons, the Si content is controlled within the
range of 0.7% to 1.5%.
[0037] Mg: 0.6% to 1.2%
[0038] Magnesium (Mg) also precipitates, with Si, mainly as a
needle-like .beta.' phase in grains upon artificial aging (temper
aging) and is necessary for imparting high strength and high yield
strength to an automobile suspension part.
[0039] Mg, if present in an excessively low content, may
precipitate in an excessively small amount upon as trial aging and
may fail to offer high strength.
[0040] In contrast, Mg, if present in an excessively high content,
may cause coarse Mg-containing compounds to be formed m grains and
at gain boundaries, and these compounds may adversely affect
corrosion resistance and toughness. In addition, such excessive Mg
may cause the hot-forged aluminum alloy to have excessively high
strength (yield strength), and this may adversely affect not only
hot forgeability and workability, but also elongation.
[0041] For these reasons, the Mg content is controlled within the
range of 0.6% to 1.2%.
[0042] Fe: 0.01% to 0.5%
[0043] Iron (Fe) forms intermetallic compounds with Si to give
dispersed particles (dispersoids). Thus, this element effectively
impedes grain boundary migration after recrystallization, restrains
recrystallization protects grains from coarsening, and contributes
to grain refinement.
[0044] In contrast, Fe, if present in an excessively high content,
tends to form coarse compounds in grains and at gain boundaries and
to cause the hot-forged aluminum alloy to have corrosion resistance
and toughness at lower levels. In addition, the intermetallic
compounds formed by Fe tend to contain Si, and the formation of
these intermetallic compounds may reduce the needle-like .beta.'
phase, because the needle-like .beta.' phase, which is formed upon
artificial aging, requires Si. This tends to cause the hot-forged
aluminum alloy to have lower strength.
[0045] For these reasons, the Fe content is controlled within the
range of 0.01% to 0.5%.
[0046] At least one element selected from Mn in a content of 0.05%
to 0.8%, Cr in a content of 0.01% to 0.5%, and Zr in a content of
0.01% to 0.2%
[0047] As with Fe, manganese (Mn), chromium (Cr), and zirconium
(Zr) than, with Si, intermetallic compounds as dispersed particles
(dispersoids), impede grain boundary migration after
recrystallization, restrain recrystallization, protect grains from
coarsening, and effectively contribute to grain refinement.
[0048] In contrast, any of Mn, Cr, and Zr, if present in an
excessively high content, tend to form coarse compounds in grains
and at grain boundaries and to cause the hot-forged aluminum alloy
to have corrosion resistance and toughness at lower levels. The
intermetallic compounds conned by these elements tend to contain
Si, and the formation of the intermetallic compounds reduces the
needle-like .beta.' phase, where the needle-like .beta.' phase,
which is formed upon artificial aging, requires Si. This tends to
cause the hot-forged aluminum alloy to have lower strength.
[0049] For these reasons, the content(s) of at least one of these
elements, when to be contained, is controlled so that the Mn
content falls within the range of 0.05% to 0.8%, the Cr content
falls within the range of 0.01% to 0.5%, and the Zr content falls
within the range of 0.01% to 0.2%.
[0050] At least one element selected from Cu in a content of 0.05%
to 1.0%, Ti in a content of 0.01% to 0.1%, and Zn in a content of
0.005% to 0.2%
[0051] Copper (Cu), titanium (TD, and zinc (Zn) are equieffective
elements to allow the forged material to have strength and
toughness at higher levels. When these effects are expected, the
hot-forged aluminum alloy may contain one or more of these elements
selectively.
[0052] Cu offers solid-solution strengthening, thereby contributes
to higher strength and better toughness of the hot-forged aluminum
alloy, and effectively significantly promotes age hardening of the
final product upon aging. Cu, if present in an excessively low
content, may fail to offer these effects on strength improvements.
In contrast, Cu, if present in an excessively high content, may
cause the microstructure of the hot-forged aluminum alloy to have
significantly high susceptibility (sensitivity) to stress corrosion
cracking and to intergranular corrosion and may thereby cause the
forged material to deteriorate in corrosion resistance and
durability. For these reasons, the content of Cu, when to be
contained, may be controlled in the range of 0.05% to 1.0%.
[0053] Zn precipitates and forms Zn--Mg precipitates finely in a
high density upon artificial aging and allows the hot-forged
aluminum alloy to have better strength and toughness. In addition,
solute Zn lowers the potential in grains and causes corrosion not
to initiate from grain boundaries, but to occur as general
corrosion. This effectively results in reduction of intergranular
corrosion and stress corrosion cracking. However, Zn, if present in
an excessively high content, may cause the hot-forged aluminum
alloy to have remarkably lower corrosion resistance. For these
reasons, the content of Zn, when to be contained, may be controlled
in the range of 0.005% to 0.2%.
[0054] Ti effectively refines grains of the ingot, allows the
microstructure of the forge material to include fine grains, and
allows the forged material to have better strength and toughness.
Ti, if pr in an excessively low content, may fail to offer these
effects. However, Ti, if present in an excessively high content,
may form coarse precipitates to lower the workability. For these
reasons, the content of when to be contained, may be controlled in
the range of 0.01% to 0.1%.
[0055] Elements listed below are impurities and may be contained in
contents up to the after-mentioned ranges. Hydrogen tends to be
included as an impurity and, particularly when the forged material
is worked at a low reduction ratio (working ratio), bubbles derived
from hydrogen resist compression bonding in working such as forging
and cause blisters, which act as fracture origins. This element
thereby causes the hot-forged aluminum alloy to have significantly
lower toughness and fatigue properties. In particular, the
influence of hydrogen is significant typically in suspension parts
designed to have higher strength. Accordingly, the hydrogen content
is preferably minimized to 0.25 ml or less per 100 g of Al.
[0056] Scandium (Sc), vanadium (V), and hafnium (Hf) also tend to
be included as impurities and adversely affect the properties of
suspension parts. To eliminate or minimize this, the total content
of these elements may be controlled to less than 03%. Boron (B)
combines with Ti and allows Ti to more effectively contribute to
grain refinement of ingots. Boron, if contained in a content
greater than 300 ppm, also forms coarse precipitates and thereby
lower the workability. For this reason, the acceptable content of
boron is set to be 300 ppm or less.
[0057] Microstructure
[0058] After controlling the forged material to have an alloy
chemical composition within the above-mentioned ranges, the present
invention specifies the microstructure of the forged material as
follows, where the forged material is for use typically as
structural components and structural parts of automobiles and other
transports and, in particular, as automobile forged suspension
parts. In the microstructure, which is a microstructure of in a
thickness central part of the forged material as measured by
SEM-EBSD analysis, grains with a misorientation of 2.degree. or
more have an average gain size of 30 .mu.m or less and have a KAM
of from 0.6.degree. to 2.0.degree. (degree), where the KAM results
from the quantification of the average misorientation of the grains
with a misorientation of 2.degree. or more.
[0059] By the grain refinement and the KAM control as above, the
present invention provides the forged material as a hot-forged
6000-series aluminum alloy that has high tensile strength, high
yield strength, and high elongation without deterioration in
corrosion resistance. The forged material, if having an excessively
low KAM of less than 0.6.degree., may fail to have high tensile
strength and/or high yield strength. The forged material, if having
an excessively high KAM of greater than 2.0.degree., may also fail
to have high tensile strength and/or high yield strength and, in
addition, may have inferior elongation.
[0060] As used herein, the term "grains with a misorientation of
2.degree. or more" as measured by SEM-EBSD analysis refers to
"gains having boundaries with a misorientation of 2.degree. or
more" and includes, in its category, many gains with a
misorientation of 2.degree. or more, for example, those with a
misorientation of 2.degree., 15.degree., or 20.degree..
[0061] It has been found in the present invention that the
refinement of grains including even grains with a relatively small
misorientation typically of 2.degree. significantly contribute to
(affect) higher strength (tensile strength and 0.2% yield
strength). On the basis of this finding, the present invention
specifies the grains as follows. Specific*, the refinement of the
grains with a misorientation of 2.degree. or more to have an
average grain size of 30 .mu.m or less allows the hot-forged
6000-series aluminum alloy to have high strength. While the
detailed reason thereof has not yet been clarified, this is
probably because as follows. Grain boundaries (borders) with a
misorientation of 2.degree. or more effectively impede dislocation
movement. Thus, the refinement of the grains to have an average
grain size of 30 .mu.m or less results in a significantly larger
number of the grain boundaries that impede dislocation movement and
may allow the forged material to have high strength.
[0062] The kernel average misorientation (KAM) in the present
invention as measured by SEM-EBSD analysis is the average
misorientation of the "gains with a misorientation 2.degree. or
more".
[0063] It is publicly known that the KAM itself has a correlation
with residual strain, as described typically in Journal of the
Society of Materials Science, Japan, Vol. 58, No. 7, pp. 568-574,
July 2009.
[0064] It is also publicly (mow n that the KAM results from the
quantification of local misorientations into an average
misorientation, where the local misorientations are each a
difference in crystal orientation between adjacent measurement
points, as described typically in the patent literature.
[0065] The KAM is defined by the formula (.SIGMA.y)/n, where n is
the number of gains; and y is a misorientation (.degree.) of each
gain as measured.
[0066] The KAM as specified in the present invention differs from
conventional equivalents in that objects to be measured for KAM are
many pains including even gains with a relatively small
misorientation such as gains with a misorientation of 2.degree., as
defined above on gains. Specifically, the RAM significantly varies
in value depending on how to specify the misorientations of grains,
where the misorientations are the basis of; or the objects of the
measurement.
[0067] It has been found in the present invention that, not only
the refine rent of grains, but also the KAM, resulting from the
average misorientation of the "gains with a misorientation of
2.degree. or more" have a strong correlation with the tensile
strength and 0.2% yield strength of the hot-forged 6000 series
aluminum alloy.
[0068] For higher strength, the KAM can be controlled by further
subjecting the hot-forged material, which is produced through hot
forging repeatedly to a combination process of relatively mild
forging in a cold to warm region with subsequent artificial aging,
without changing the 6000-series aluminum alloy chemical
composition of the hot-forged material, which chemical composition
has already been standardized typically for the automobile
suspension parts.
[0069] Accordingly, a hot-forged 6000-series aluminum alloy having
high tensile strength, high yield strength, and high elongation can
be produced without deterioration in corrosion resistance and
without changes in mechanical properties, where the deterioration
and changes are caused by changes in chemical composition and hot
forging conditions. This allows the hot-forged 6000-series aluminum
alloy to offer better reliability as safety-related parts typically
in automobile suspension parts.
[0070] In addition, the microstructure and the properties as
specified in the present invention can be advantageously achieved
even when the hot-forged material is produced through hot forging
at a high reduction ratio in terms of minimum reduction in wall
thickness of greater than 25%, because the hot forging is not
changed in conditions.
[0071] For example, a forged suspension part, to which the present
invention is applied, generally has a complicated shape as follows.
The forged suspension part generally has an approximately
triangular shape as a whole and includes an arm portion having an
approximately Y shape, and ball joint portions (three portions)
disposed at the three ends of the arm portion. The forming of such
a complicated shape inevitably requires a high reduction ratio in
terms of minimum reduction in wall thickness of greater than 25%.
The present invention can provide the specific microstructure and
the specific properties even through hot forging performed at such
a high reduction ratio.
[0072] Site of Measurement by SEM-EBSD Analysis
[0073] The average grain size (.mu.m) and KAM of the grains with a
misorientation of 2.degree. or more are measured in a thickness
central part of the forged material. When the forged material has a
simple shape such as a char or cylindrical shape, the thickness
central part of the forged material to be measured can be specified
on the basis of the center of the forged material. However, the
automobile suspension parts representatively have a complicated
shape as follows. This shape is an approximately triangular shape
as a whole in a plan view. Ball joints at the three apices of the
triangle are coupled to each other through arms. The arms each
include ribs and a web, where the ribs are in the periphery and
have a narrow width and a large thickness, and the web is in the
central portion and has a wide width and a small thickness. The
arms each have an approximately H- or U-shaped cross section.
Accordingly the "Thickness central part" in this case is defined
herein as the center of the thickness at any position of the thick
ribs, and the grain microstructure in the thickness central part is
defined as the measurement object to be measured by SEM-EBSD
analysis.
[0074] Measurement Method
[0075] Specifically, the measurement may be performed in the
following manner. Three measurement samples are sampled from any
positions of the thickness central part of the thick ribs, and are
polished to give MSS sections. A measurement region of 500 .mu.m by
500 .mu.m of the cross section of each sample parallel to the
compression direction of the forged material is irradiated with
electron beams at a pitch of 1.0 .mu.m using an SEM-EBSD system.
The average grain size (.mu.m) of grains with a misorientation of
2.degree. or more, and the KAM resulting from quantification of the
average re orientation of the grains are measured, and the three
measurements (n=3) are averaged.
[0076] The SEM-EBSD (EBSP) analysis is a crystal orientation
analysis technique using a field emission scanning electron
microscope (FESEM) equipped with an electron back scattering
(scattered) diffraction pattern (EBSD, EBSP) analysis
s<stem.
[0077] More specifically, the samples to be observed by SEM-EBSD
analysis may be prepared in the following manner. The observation
samples (cross-sectional microstructures) are further mechanically
polished and then electrically etched to have a mirror surface.
Each of the resulting samples is set in the lens barrel of the
FESEM, and electron beams are applied to the mirror surface of the
sample to project an EBSP on the screen. An image of this is taken
by a highly sensitive camera and captured as an image into a
computer. In the computer, the image is analyzed and compared with
patterns obtained by simulation on known crystal systems, and on
the basis of the comparison, crystal orientations are determined.
The determined crystal orientations are recorded as
three-dimensional Eulerian angles typically with position
coordinates (x, y, z). This process is automatically performed on
all measurement points, and gives crystal orientation data at
several tens of thousands to several hundreds of thousands of
points upon the completion of measurement.
[0078] The hot-forged aluminum alloy according to the present
invention, which has the alloy chemical composition and the
microstructure, preferably has a tensile strength of 420 MPa or
more, a 0.2% yield strength of 400 MPa or more, and an elongation
of 12% or more. This is preferred in consideration of strength and
workability.
[0079] Production Method
[0080] Next, a method for producing the hot-forged aluminum alloy
wording to the present invention will be illustrated. The
production process for the hot-forged aluminum alloy in the present
invention by itself can be performed by a common procedure, in
which an aluminum alloy ingot having the chemical composition is
subjected sequentially to homogenization and hot forging to give a
forged material, and the forged material is subjected sequentially
to solution treatment, quenching, and artificial aging. Namely, the
hot-forged aluminum alloy can be produced without a hot extrusion
step of the ingot, which is an extra step. However, there are
preferred production conditions as follows, so as to allow the
resulting hot-forged aluminum alloy to have the microstructure and
to have high strength, high toughness, and high corrosion
resistance, where the properties are suitable typically for
automobile forged suspension pmts.
[0081] Casting
[0082] Casting of a molten aluminum alloy, which is melted and
adjusted to have an aluminum alloy chemical composition within the
specific range, may be performed by a common melt casting
technique. The melt casting technique may be selected as
appropriate typically from continuous casting-directed rolling,
semicontinuous casting (direct chill (DC) casting), and hot top
casting.
[0083] However, the casting of the molten aluminum alloy having an
aluminum alloy chemical composition within the specific range is
preferably performed at an average cooling rate of 100.degree. C./s
or more, for refinement of precipitates and decrease of secondary
dendrite arm spacing (secondary DAS).
[0084] Homogenization (Soaking)
[0085] The homogenization (soaking) of the ingot after casting may
be performed by holding the ingot in a temperature range of
450.degree. C. to 580.degree. C. for 2 hours or longer. The
homogenization, if performed at a temperature lower than
450.degree. C., may fail to homogenize the ingot due to such
excessively low temperature. In contrast, the homogenization, if
performed at a temperature higher than 580.degree. C., may cause
burring of the ingot surface. Extrusion after homogenization and
before hot forging is not necessary, but may be performed when
desired.
[0086] Hot Forging
[0087] The ingot after the homogenization is reheated and subjected
to hot forging performed preferably at a material temperature of
from 430.degree. C. to 550.degree. C., a forming die temperature of
from 100.degree. C. to 250.degree. C., a minimum reduction in wall
thickness of 25% or more, and a maximum reduction m v all thickness
of 90% or less.
[0088] The hot forging may be performed using a mechanical press or
using an oil hydraulic press so as to forge the ingot to a final
product shape (or a near net shape) of an automobile suspension
part. The hot forging may be performed multiple times, including
rough forging, intermediate forging, and finish forging, without
reheating or with reheating as needed during forging.
[0089] The hot forging, if performed at a minimum reduction in wall
thickness less than 25% may fail to give the automobile suspension
part having the complicated shape with good shape precision by
forging, where the minimum reduction in wall thickness is
considered as a hot forging reduction ratio. In contrast, the hot
forging, if performed at a maximum reduction in wall thickness
greater than 90%, may hardly restrain recrystallization and may
highly possibly cause coarse recrystallized grains to be
formed.
[0090] The hot forging, if performed at a forging end temperature
after final forging of lower than 300.degree. C., may impede
restrainment of recrystallization during forging and solution
treatment processes, and this may cause a deformed microstructure
to be recrystallized to form coarse grains. These coarse gains, if
formed, may impede the forged material from having higher strength
and better toughness and may cause the forged material to have
lower corrosion resistance, even when the fined material is
conformed to have the above-mentioned microstructure. In addition,
hot forging, if performed at such a low temperature, may impede
refinement of grains in the entire region in a cross section of the
forged material. In contrast, the hot forging, if performed at a
material temperature higher than 550.degree. C., may highly
possibly cause burning of the forged material surface and cause
coarse recrystallized gains to be formed.
[0091] Solution Treatment and Quenching
[0092] The work after the hot forging is subjected to solution
treatment and quenching. In the solution treatment, the work is
preferably held in a temperature range of 530.degree. C. to
570.degree. C. for a time of 1 hour to 8 hours. The solution
treatment, if performed at an excessively low temperature and/or
for an excessively short time, may become insufficient and may
cause insufficient solid-solution of Mg--Si compounds. This may
cause the compounds to precipitate in an excessively small amount
in the subsequent artificial aging and cause the forged material to
have lower strength. The solution treatment may be performed for a
long holding time, but may offer saturated effects when performed
for a time longer than 8 hours.
[0093] After the solution treatment, the work is preferably
subjected to quenching at an average cooling rate of 25.degree.
C./s or more in the temperature range of from 500.degree. C. down
to 100.degree. C. The cooling in the quenching is preferably
performed by water cooling, and particularly preferably performed
by water cooling (water tank immersion) in which cooling water is
circulated with bubbling. This is preferred for ensuring the
above-mentioned average cooling rate and for performing homogeneous
cooling to eliminate or minimize strain of the forged material. The
quenching treatment, if performed at an excessively low cooling
rate, may cause precipitation typically of Mg--Si compounds and Si
at grain boundaries and may thereby cause the product after
artificial aging to be susceptible to grain boundary fracture and
to have toughness and fatigue properties at lower levels. In
addition, such quenching treatment at an excessively low cooling
rate may cause Mg--Si compounds and Si, which are stable phases, to
be formed also in grains in the course of cooling. This may cause a
.beta. phase and a .beta.' phase to precipitate in smaller amounts
upon artificial aging and may cause the forged material to have
lower strength.
[0094] In contrast, the quenching, if performed at an excessively
high cooling rate of the forged material is cooled excessively
rapidly), may cause hardening strain during quenching to be formed
in a large amount, and this may disadvantageously require an extra
correcting process after quenching, or may cause the correcting
process to include a larger number of steps. In addition, such
quenching performed at an excessively high cooling rate gives
higher (greater) residual stress and may cause the product to have
dimensional precision and shape precision at, lower levels. In
consideration of these, the quenching is preferably performed as
hot-water quenching at 30.degree. C. to 85.degree. C., at which
temperature quenching strain is relaxed. This is preferred for
shortening the product production process and lowering the cost.
The hot-water quenching, if performed at a temperature lower than
30.degree. C. may cause greater quenching strain. The hot-water
quenching, if perforated at a temperature higher than 85.degree. C.
may cause the forged material to have toughness, fatigue
properties, and strength at lower levels, due to an excessively low
cooling rate.
[0095] Cold Working or Warm Working
[0096] In the present invention, the hot-forged material (after
solution treatment and quenching) obtained in the above manner is
preferably subjected to a combination process of cold working or
warm working with subsequent artificial aging after each working,
where the combination process is performed repeatedly at least two
times, and where the cold working or warm working is performed at a
total reduction in thickness of 5% or more in the temperature range
of morn temperature to 200.degree. C. This combination process is
performed so as to allow the hot-forged material to have an average
grain size and a KAM within the specified ranges.
[0097] Assume that the combination process of cold working or warm
working with subsequent artificial aging is performed only once, or
cold working or warm working is performed even two times but
artificial aging is not performed after each cold or warm working.
In this case, the resulting hot-forged material may fail to have an
average gain size and a KAM both within the specified ranges.
[0098] In other words, the repetition of two or mom times of the
combination process of cold working or warm working with subsequent
artificial aging performed after each working surely allows the
resulting forged material to have an average grain size and a KAM
of gains with a misorientation of 2.degree. or more both within the
specified ranges.
[0099] The cold working or warm working, if performed at a low
reduction in thickness of less than 5% per one process, may fail to
exhibit sufficient effects and may cause the forged material to
have a large (coarse) average grain size of grains with a
misorientation of 2.degree. or more of greater than 30 .mu.m. The
cold working or warm working in this case also tends to cause the
forged material to have a low KAM of less than 0.6.degree. and to
fail to have the desired high strength.
[0100] This is also true in the case where the warm working is
performed at an excessively high working temperature of higher than
200.degree. C. Specifically, the warm working in this case may
cause the forged material to have a large (coarse) average grain
size of grains with a misorientation of 2.degree. or more of
greater than 30 .mu.m, to tend to have a low KAM of less than
0.6.degree., and to fail to have the desired high strength.
[0101] In contrast the upper limit of the reduction in thickness
per one process of the cold worker or warm working is preferably
50%, and more preferably 40%. The cold or warm working, if
performed at an excessively high reduction in thickness to cause
excessively large strain, may cause the forged material to have an
excessively low elongation due to an excessively high KAM. In
addition, the working in this case tends to cause cracking during
working.
[0102] In this regard, with the techniques disclosed in PLT 2 and
PTL 3, significantly large strain is applied to the work in warm
working. Specifically, with the technique disclosed in PTL 2, the
warm wilting is performed at a wilting ratio in terms of reduction
in thickness of greater than 85% by the application of an
equivalent strain of 2 or more. With the technique disclosed in PTL
3, an equivalent strain of less than 2 is applied, but, in the
working examples, the warm working is performed at a working ratio
in terms of reduction in thickness of 55% by the application of an
equivalent strain of 0.8. If such significantly large strain is
applied, the hot-forged 6000-series aluminum alloy according to the
present invention and even the 6000-series aluminum alloy ingots
disclosed in PTL 2 and PTL 3 each have a significantly low
elongation, although having high strength.
[0103] For these reasons, cold working or warm working is performed
at a reduction in thickness per one process of preferably 5% to
50%, and more preferably 5% to 40%.
[0104] Artificial Aging
[0105] After each cold or warm working, artificial aging is
performed. The combination process of cold or warm working with
subsequent artificial aging is performed repeatedly at least two
times. To impede natural aging at mom temperature from proceeding,
the artificial aging is preferably performed immediately (typically
within cane hour, as a rough reference) after each cold or warm
working.
[0106] The artificial aging conditions in each process are
preferably selected within a temperature range of 40.degree. C. to
250.degree. C. and within a holding time range of 20 minutes to 8
hours.
[0107] However, even within the condition ranges, optimum
conditions should be selected corresponding to the chemical
composition of the forged material and the conditions of previous
processes such as hot forging, solution treatment, quenching
treatment, and cold or warm working. Assume that the artificial
aging is performed under conditions not corresponding to the
chemical composition and the previous process conditions and
performed at an excessively low or an excessively high temperature,
or for an excessively short holding time. In, this case, the
artificial aging may impede the forged material from having the
desired, specified microstructure and from having high tensile
strength, high yield strength, and high elongation.
[0108] The homogenization and solution treatment as mentioned above
may be performed using an apparatus selected as appropriate
typically from air furnaces, induction heating furnaces (induction
heaters), and salt-bath furnaces. The artificial aging may be
performed using an apparatus selected as appropriate typically from
air furnaces, induction heating furnaces, and oil baths.
[0109] The forged material according to the present invention, when
to be used in or as an automobile suspension part, may be subjected
to one or more processes, such as machining and surface treatments,
as appropriate before and/or after the artificial aging.
[0110] The present invention will be illustrated in further detail
with reference to several experimental examples below. It should be
noted, however, that the examples are by no means intended to limit
the scope of the invention; that various changes and modifications
can naturally be made therein without departing from the spirit and
scope of the invention as described herein; and that all such
changes and modifications should be considered to be within the
scope of the invention.
Examples
[0111] Next, the present invention will be illustrated with
reference to several examples (experimental examples). Forged
materials as materials for automobile suspension parts were
produced in the following manner. Initially, materials having
aluminum alloy chemical compositions given in Table 1 were prepared
and subjected to solution treatment and quenching under common
conditions. The works (materials) were then subjected sequentially
to cold or warm working and subsequent artificial aging under
different conditions given in Table 2 and yielded the hot-forged
materials. The resulting hot-forged materials were subjected to
measurements and evaluations on microstructure, mechanical
properties, and corrosion resistance, as presented in Table 2.
[0112] Specifically, ingots having chemical compositions
corresponding to the hot-forged 6000-series aluminum alloy chemical
compositions given in Table 1 were prepared by casting via
semicontinuous casting at an average cooling rate of 100.degree.
C./s or more, in common in each sample. All the aluminum alloy
samples given in Table 1 had, in common, a hydrogen content of 0.10
to 0.15 ml per 100 g of Al.
[0113] In common in each sample, the outer surface of each of the
aluminum alloy ingots was faced by a thickness of 3 mm and cut into
a round rod-like billet having a length of 120 mm and a diameter of
75 mm. The billet was homogenized (soaked) at 520.degree. C. for 5
hours and thereafter cooled via, forced wind cooling using a fan at
a moiling rate of 100.degree. C./hr or more.
[0114] The ingot after homogenization was subjected to hot forging,
in which forging was performed three times down to a final wall
thickness via mechanical press forming using upper and lower dies
in common in each sample. The forging was performed under common
conditions at a forging start temperature in the range of
500.degree. C. to 520.degree. C., a forming die temperature in the
range of 170.degree. C. to 200.degree. C., and a wall thickness
change of 75% (greater than 25%) in the central part of the forged
material.
[0115] The hot-forged materials after production had a suspension
part shape in common in each sample. The suspension part shape is
an approximately triangular shape as a whole in a plan view. Ball
joints at the three apices of the triangle are coupled to each
other though arms. The arms each include ribs and a web, where the
ribs are in the periphery and have a narrow width and a large
thickness (height) of 60 mm, and the web is in the central portion
and has a wide width and a small thickness (height) of 31 mm. The
arms each have an approximately H-shaped cross section.
[0116] These forged materials were, in common in each sample,
subjected to solution treatment at 550.degree. C. for 5 hours using
an air furnace and then subjected to the water cooling (water tank
immersion) at an average cooling rate of 25.degree. C./s or more in
the temperature mange of from 500.degree. C. down to 100.degree.
C.
[0117] The hot-forged materials (after solution treatment and
quenching) obtained in the above manner were different in average
grain size and/or KAM typically by subjecting them to cold working
or warm working in combination with subsequent artificial aging two
times or only once under different conditions given in Table 2.
[0118] The resulting hot-forged materials being different in
average grain size and/or KAM of grains as above were subjected to
measurements and evaluations on microstructure, mechanical
properties, and resistance to intergranular stress corrosion
cracking by the following methods. The results of these
measurements and evaluations are given in Table 2.
[0119] Microstructure
[0120] The average grain size and KAM of grains were individually
measured by the above-mentioned measurement method. Specifically,
samples were sampled from a longitudinal section in any thickness
central part of a thick rib in any of the approximately H-shaped
arms of the forged material. Of the samples, the average grain
sized (.mu.m) and KAM of grains with a misorientation of 2.degree.
or more were measured by the procedure mentioned above.
[0121] Mechanical Properties
[0122] A sample was sampled from the thickness central part at any
position of the thick rib of the forged material. From the sample,
three tensile test specimens direction) having an outer diameter of
5 mm and a gauge length of 25 mm were prepared at any three points
in the longitudinal direction of the sample, on which mechanical
properties such as tensile strength (MPa), 0.2% yield strength
(MPa), and elongation (%) were measured, and the average of the
three measurements (at the three points) was determined.
[0123] Stress Corrosion Cracking Resistance
[0124] The stress corrosion cracking resistance was evaluated in
conformity with the alternate immersion test prescribed in JIS H
8711. FIGS. 1A and 1B area side view and a plan view, respectively,
of the test specimen for stress corrosion cracking resistance
evaluation (C-ring test specimen for SCC test), including its
dimensions. When a stress of 300 MPa was applied, a sample
undergoing stress corrosion cracking within a time period shorter
than 30 days was evaluated as having poor corrosion resistance (x),
and a sample undergoing stress corrosion mucking within a time
period from 30 days to shorter than 60 days was evaluated as having
good corrosion resistance (.largecircle.).
[0125] As clearly demonstrated by the data in Tables 1 and 2,
Examples 1 and 7 to 12 had chemical compositions within the range
specified in the present invention and underwent cold working or
warm working and artificial aging under conditions within the
preferred ranges. As demonstrated by the data in Table 2, these
examples therefore had microstructures as specified in the present
invention. Specifically, in the microstructure of the thickness
central part, grains with a misorientation of 2.degree. or more had
an average gain size of 30 .mu.m or less and a KAM of from
0.6.degree. to 2.0.degree., as measured by SEM-EBSD analysis.
[0126] As a result, the examples have excellent stress corrosion
cracking resistance and still have high strength in terms of
tensile strength of 417 MPa or more, high yield strength in terms
of 0.2% yield strength of 398 MPa or more, and a high elongation of
12.6% or more. Thus, the examples can combine the properties
necessary for suspension parts.
[0127] In contrast, Comparative Examples 2 to 6 in Table 2 are
samples having chemical compositions within the ranges, but being
produced via cold working or warm working and artificial aging
performed under conditions out of the preferred ranges. These
samples (comparative examples) failed to meet any of the conditions
specified on microstructure in the thickness central part, where
the microstructure is me cured by SEM-EBSD analysis. Specifically,
these comparative examples had an excessively large average grain
size of grains with a misorientation of 2.degree. or more of gaiter
than 30 .mu.m (included coarsened grains), or had an excessively
low KAM of less than 0.6.degree., or had an excessively high KAM of
greater than 2.0.degree..
[0128] As a result, Comparative Examples 2 to 6 had, in common,
significantly lower tensile strength and 02% yield strength as
compared with the examples. Of the comparative examples, the sample
having an excessively high RAM of grater than 2.0.degree. also had
a lower elongation as compared with the examples.
[0129] Comparative Example 2 underwent the combination process of
warm working and subsequent artificial aging performed only once.
This sample therefore had an excessively large (coarse) average
grain size of grains with a misorientation of 2.degree. or more of
greater than 30 .mu.m and had an excessively low KAM of less than
0.6.degree..
[0130] Comparative Example 3 underwent the combination process of
warm working and subsequent artificial aging performed in this
sequence two times, but underwent the warm working performed at an
excessively small reduction in thickness (reduction ratio). This
sample therefore had an excessively large (coarse) average gain
size of gains with a misorientation of 2.degree. or more of greater
than 30 .mu.m and had an excessively low KAM of less than
0.6.degree..
[0131] Comparative Example 4 underwent the combination process of
warm working and artificial aging performed in this sequence two
times, but underwent the warm working performed at an excessively
high temperature both in the two processes. This sample therefore
had an excessively large (coarse) average grain size of grains with
a misorientation of 2.degree. or more of greater than 30 .mu.m and
had an excessively low KAM of less than 0.6.degree..
[0132] Comparative Example 5 underwent warm working repeated two
times, but underwent no artificial aging after the second warm
working. This sample had an average grain size of grains with a
misorientation of 2.degree. or more of 30 .mu.m or less, but had an
excessively high KAM of greater them 2.0.
[0133] Comparative Example 6 underwent the combination process of
warm working and subsequent artificial aging performed in this
sequence two times, but underwent the artificial aging performed at
an excessively high temperature both in the two processes. This
sample therefore had an excessively large (coarse) average grain
size of grains with a misorientation of 2.degree. or more of
greater than 30 .mu.m and had an excessively low KAM of less than
0.6.degree..
[0134] Comparative Examples 13 to 24 in Table 2 employed Alloy Nos.
8 to 18 in Table 1, which are alloys having chemical compositions
out of the ranges. These comparative examples were low in one or
more of tensile strength, 0.2% yield strength, elongation, and
stress corrosion cracking resistance as compared with the examples,
even when the comparative examples were produced through cold
working or warm working and artificial aging performed under
conditions within the preferred ranges, regardless of whether they
met the conditions in microstructure in the thickness central part,
as measured by SEM-EBSD analysis.
[0135] Specifically, samples having high tensile strength and/or
high yield strength as with the examples had a lower elongation or
significantly lower stress corrosion cracking resistance as
compared with the examples. Samples having high elongation or good
stress mansion cracking resistance as with the examples had tensile
strength and 0.2% yield strength at significantly lower levels as
compared with the examples.
[0136] Comparative Example 13 had an excessively low Mg content
(Alloy No. 8 in Table 1).
[0137] Comparative Example 14 had an excessively high Mg content
(Alloy No. 9 in Table 1).
[0138] Comparative Examples 15 and 16 each had an excessively low
Si content (Alloy No. 10 in Table 1). Among them, Comparative
Example 16 underwent warm working and subsequent artificial aging
performed only once.
[0139] Comparative Example 17 had an excessively high Si content
(Alloy No. 11 in Table 1).
[0140] Comparative Examples 18 and 19 contained none of Mn, Cr, and
Zr, or contained one of these elements in an excessively low
content (Alloy Nos. 12 and 13 in Table 1).
[0141] Comparative Example 20 had an excessively high Mn content
(Alloy No. 14 in Table 1).
[0142] Comparative Examples 21, 22, 23, and 24 respectively had an
excessively high content of Cr, Zr, Cu, and Zn (Alloy Nos. 15, 16,
17, and 18 in Table 1).
[0143] These results demonstrate the critical significance of the
conditions specified in the present invention on chemical
composition and microstructure to give hot-forged 6000-series
aluminum alloys that have excellent corrosion resistance and still
have high tensile strength, high yield strength, and high
elongation.
TABLE-US-00001 TABLE 1 Chemical composition of forged 6000-series
aluminum alloy Alloy (in mass percent; the remainder: Al) number Mg
Si Fe Mn Cr Zr Cu Ti Zn 1 0.76 1.04 0.10 0.31 -- -- -- -- -- 2 0.85
1.04 0.08 0.15 0.06 0.05 -- -- -- 3 0.69 1.15 0.09 0.65 -- -- -- --
-- 4 1.00 0.85 0.09 -- 0.31 -- 0.08 0.06 -- 5 0.73 0.89 0.17 -- --
0.14 -- -- 0.02 6 0.69 0.81 0.32 0.26 -- -- 0.63 -- -- 7 0.71 1.40
0.08 0.30 0.09 -- -- 0.02 -- 8 0.53 0.97 0.07 0.28 0.05 -- -- -- --
9 1.80 1.15 0.10 0.26 0.09 -- -- -- -- 10 1.00 0.65 0.10 0.28 0.06
-- -- -- -- 11 0.83 1.84 0.14 0.30 0.09 -- -- -- -- 12 0.84 0.95
0.11 -- -- -- -- -- -- 13 0.83 0.95 0.07 0.02 -- -- -- -- -- 14
0.84 0.96 0.07 1.02 -- -- -- -- -- 15 0.77 0.96 0.14 -- 0.71 -- --
-- -- 16 0.79 0.97 0.09 -- -- 0.47 -- -- -- 17 0.77 0.96 0.14 0.29
0.08 -- 1.17 -- -- 18 0.77 0.99 0.13 0.35 -- -- -- -- 0.53
TABLE-US-00002 TABLE 2 Production method for forged 6000-series
aluminum alloy Cold or warm working and subsequentartificial aging
after solution treatment Alloy First working Second working number
Working Reduction in Working Reduction in in Table temperature
thickness First artificial temperature thickness Second artificial
Categoy Number 1 (.degree. C.) (%) aging (.degree. C.) (%) aging
Example 1 1 150 10 180.degree. C. for 1 hr 150 10 180.degree. C.
for 1 hr Comparative 2 1 180 50 180.degree. C. for 1 hr -- -- --
Example 3 1 180 2 180.degree. C. for 1 hr 180 2 180.degree. C. for
1 hr 4 1 250 10 180.degree. C. for 1 hr 250 10 180.degree. C. for 1
hr 5 1 150 20 180.degree. C. for 1 hr 150 30 -- 6 1 150 10
260.degree. C. 0.5 hr 150 10 260.degree. C. for 0.5 hr Example 7 2
100 30 190.degree. C. for 1 hr 180 20 160.degree. C. for 5 hr 8 3
120 20 120.degree. C. for 1 hr 150 30 210.degree. C. for 0.5 hr 9 4
140 20 150.degree. C. for 1 hr 120 30 190.degree. C. for 1 hr 10 5
room 10 150.degree. C. for 1 hr room 20 190.degree. C. for 1 hr
temperature temperature 11 6 200 20 180.degree. C. for 1 hr 130 5
60.degree. C. for 5 hr 12 7 60 10 130.degree. C. for 1 hr 60 30
160.degree. C. for 5 hr Comparative 13 8 150 40 150.degree. C. for
1 hr 150 5 190.degree. C. for 1 hr Example 14 9 90 30 100.degree.
C. for 5 hr 200 10 160.degree. C. for 5 hr 15 10 120 10 120.degree.
C. for 1 hr 150 20 190.degree. C. for 1 hr 16 10 200 50 180.degree.
C. for 1 hr -- -- -- 17 11 100 30 100.degree. C. for 5 hr 200 10
190.degree. C. for 1 hr 18 12 130 30 140.degree. C. for 1 hr room
10 180.degree. C. for 1 hr temperature 19 13 120 40 120.degree. C.
for 1 hr 150 10 190.degree. C. for 1 hr 20 14 130 5 140.degree. C.
for 1 hr 60 30 160.degree. C. for 5 hr 21 15 80 20 100.degree. C.
for 5 hr 150 20 190.degree. C. for 1 hr 22 16 150 20 150.degree. C.
for 1 hr 180 10 180.degree. C. for 5 hr 23 17 140 10 150.degree. C.
for 1 hr 150 20 190.degree. C. for 1 hr 24 18 170 10 180.degree. C.
for 1 hr 150 20 190.degree. C. for 1 hr Properties of forged
6000-series aluminum alloy Average grain size of grains with KAM of
0.2% Stress misorientation grains with a Tensile Yield corrosion of
2.degree. or more misorientation strength strength Elongation
cracking Categoy Number .mu.m of 2.degree. or more MPa MPa %
resistence Example 1 22 0.8 417 398 15.2 .smallcircle. Comparative
2 33 0.5 392 374 16.3 .smallcircle. 3 35 0.4 378 358 15.8
.smallcircle. Example 4 42 0.4 354 331 14.6 .smallcircle. 5 26 2.1
394 388 6.5 .smallcircle. 6 38 0.5 343 316 15.3 .smallcircle.
Example 7 18 0.9 458 434 16.3 .smallcircle. 8 16 0.8 450 419 12.6
.smallcircle. 9 18 1.2 422 402 13.1 .smallcircle. 10 16 1.6 431 415
15.7 .smallcircle. 11 15 1.0 463 442 18.8 .smallcircle. 12 18 1.1
451 438 14.6 .smallcircle. Comparative 13 26 0.8 374 355 16.6
.smallcircle. Example 14 14 1.1 420 403 5.9 .smallcircle. 15 18 0.8
368 368 15.2 .smallcircle. 16 32 0.7 378 356 14.7 .smallcircle. 17
16 1.0 427 406 5.7 .smallcircle. 18 40 0.8 377 352 18.6
.smallcircle. 19 36 0.9 391 369 16.8 .smallcircle. 20 14 1.3 388
381 5.1 .smallcircle. 21 16 1.2 380 369 3.7 .smallcircle. 22 18 1.2
381 373 4.5 .smallcircle. 23 18 0.9 453 423 18.3 x 24 22 0.8 406
391 15.3 x
[0144] While the present invention has been particularly described
with reference to specific embodiments thereof, it is obvious to
those skilled in the art that various changes and modifications may
be made without departing from the spirit and scope of the present
invention.
[0145] This application claims priority to Japanese Patent
Application No. 2015-123043, filed on Jun. 16, 2015, the entire
contents of which are incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0146] The present invention can provide hot-forged 6000-series
aluminum alloys that have excellent corrosion resistance and still
have high tensile strength, high yield strength, and high
elongation. The present invention can therefore enlarge the
applications of hot-forged 6000-series aluminum alloys to
automobile suspension parts and other parts or components of
transports such and has significant industrial value.
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