U.S. patent application number 10/468971 was filed with the patent office on 2004-05-20 for aluminum alloy sheet excellent in formability and hardenability during baking of coating and method for production thereof.
Invention is credited to Asano, Mineo, Furuyama, Tsutomu, Minoda, Tadashi, Ozeki, Yoshikazu, Uchida, Hidetoshi.
Application Number | 20040094249 10/468971 |
Document ID | / |
Family ID | 27567028 |
Filed Date | 2004-05-20 |
United States Patent
Application |
20040094249 |
Kind Code |
A1 |
Uchida, Hidetoshi ; et
al. |
May 20, 2004 |
Aluminum alloy sheet excellent in formability and hardenability
during baking of coating and method for production thereof
Abstract
A sheet of a 6000 type aluminum alloy containing Si and Mg as
main alloy components and having excellent formability sufficient
to allow flat hemming, excellent resistance to denting, and good
hardenability during baking a coating, which exhibits an anisotropy
of Lankford values of more than 0.4 or the strength ratio for cube
orientations of the texture thereof of 20 or more, and exhibits a
minimum bend radius of 0.5 mm or less at 180.degree. bending even
when the offset yield strength thereof exceeds 140 MPa through
natural aging; and a method for producing the sheet of the aluminum
alloy, which comprises subjecting an ingot to a homogenization
treatment, cooling to a temperature lower than 350.degree. C. at a
cooling rate of 100.degree. C./hr or more, optionally to room
temperature, heating again to a temperature of 300 to 500.degree.
C. and subjecting it to hot rolling, cold rolling the hot rolled
product, and subjecting the cold rolled sheet to a solution
treatment at a temperature of 400.degree. C. or higher, followed by
quenching.
Inventors: |
Uchida, Hidetoshi; (Nagoya
City, JP) ; Minoda, Tadashi; (Nagoya City, JP)
; Asano, Mineo; (Toyoake City, JP) ; Ozeki,
Yoshikazu; (Nagoya City, JP) ; Furuyama, Tsutomu;
(Nagoya City, JP) |
Correspondence
Address: |
Flynn Thiel Boutell & Tanis
2026 Rambling Road
Kalamazoo
MI
49008-1699
US
|
Family ID: |
27567028 |
Appl. No.: |
10/468971 |
Filed: |
August 22, 2003 |
PCT Filed: |
March 26, 2002 |
PCT NO: |
PCT/JP02/02900 |
Current U.S.
Class: |
148/693 ;
148/415 |
Current CPC
Class: |
C22C 21/02 20130101;
C22C 21/08 20130101; C22F 1/043 20130101; C22F 1/047 20130101; C22C
21/06 20130101; C30B 25/18 20130101; C30B 29/02 20130101; C22F 1/05
20130101 |
Class at
Publication: |
148/693 ;
148/415 |
International
Class: |
C22F 001/04; C22C
021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 28, 2001 |
JP |
2001-091979 |
Mar 28, 2001 |
JP |
2001-091980 |
Sep 27, 2001 |
JP |
2001-295633 |
Mar 8, 2002 |
JP |
2002-063118 |
Mar 8, 2002 |
JP |
2002-063119 |
Mar 20, 2002 |
JP |
2002-077794 |
Mar 20, 2002 |
JP |
2002-077795 |
Claims
1. An aluminum alloy sheet with excellent formability and paint
bake hardenability, which comprises Si and Mg as major alloy
components, the aluminum alloy sheet having a minimum inner bending
radius of 0.5 mm or less by 180.degree. bending after 10% tensile
stretching, even if yield strength of the aluminum alloy sheet
exceeds 140 MPa through natural aging after a solution heat
treatment and quenching.
2. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 1, which comprises 0.5-1.5%
(mass %, hereinafter the same) of Si and 0.2-1.0% of Mg, with the
balance consisting of Al and impurities.
3. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 1, which comprises 0.5-1.5%
of Si and 0.2-1.0% of Mg, with the balance consisting of Al and
impurities, in which the maximum diameter of Mg--Si compounds is 10
.mu.m or less and the number of Mg--Si compounds having a diameter
of 2-10 .mu.m is 1000 per mm.sup.2 or less.
4. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 2 or 3, which further
comprises 0.1-0.3% of Zn.
5. An aluminum alloy sheet with excellent formability and paint
bake hardenability, which comprises 0.8-1.2% of Si, 0.4-0.7% of Mg,
and 0.1-0.3% of Zn, with the balance consisting of Al and
impurities, in which the maximum diameter of Mg--Si compounds is 10
.mu.m or less and the number of Mg--Si compounds having a diameter
of 2-10 .mu.m is 1000 per mm.sup.2 or less, the aluminum alloy
sheet having a minimum inner bending radius of 0.2 mm or less by
180.degree. bending after 10% tensile stretching, even if yield
strength of the aluminum alloy sheet exceeds 140 MPa through
natural aging after a solution heat treatment and quenching.
6. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to any one of claims 1-5, which
further comprises at least one of 0.3% or less (excluding 0%,
hereinafter the same) of Mn, 0.3% or less of Cr, 0.2% or less of V,
and 0.15% or less of Zr.
7. An aluminum alloy sheet with excellent formability and paint
bake hardenability, which comprises 0.4-1.5% of Si, 0.2-1.2% of Mg,
and 0.05-0.3% of Mn, with the balance consisting of Al and
impurities, in which the percentage of crystal grain boundaries in
which misorientation of adjacent crystal grains is 15.degree. or
less is 20% or more.
8. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 7, which further comprises
0.5% or less of Zn.
9. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 7 or 8, which further
comprises at least one of 0.3% or less of Cr, 0.2% or less of V,
and 0.15% or less of Zr.
10. An aluminum alloy sheet with excellent formability and paint
bake hardenability, which comprises Si and Mg as major alloy
components, in which an anisotropy of Lankford values is more than
0.4.
11. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 10, which comprises 0.5-2.0%
of Si and 0.2-1.5% of Mg, with 0.7Si %+Mg %.ltoreq.2.2%, and Si
%-0.58Mg %.gtoreq.0.1% being satisfied and the balance consisting
of Al and impurities.
12. An aluminum alloy sheet with excellent formability and paint
bake hardenability, which comprises Si and Mg as major alloy
components, in which an intensity ratio of cube orientation of
crystal graphic texture is 20 or more.
13. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 12, which comprises 0.5-2.0%
of Si and 0.2-1.5% of Mg, with 0.7Si %+Mg %.ltoreq.2.2% being
satisfied and the balance consisting of Al and impurities.
14. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to claim 11 or 13, which further
comprises 0.5% or less of Zn.
15. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to any one of claims 11, 13, and 14,
which further comprises at least one of 1.0% or less of Mn, 0.3% or
less of Cr, 0.2% or less of V, and 0.2% or less of Zr.
16. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to any one of claims 2-9, 11, and
13-15, which further comprises 1.0% or less of Cu.
17. The aluminum alloy sheet with excellent formability and paint
bake hardenability according to any one of claims 2-9, 11, and
13-16, which further comprises at least one of 0.1% or less of Ti
and 50 ppm or less of B.
18. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 2-6, 16, and 17, the method comprising homogenizing an ingot
of an aluminum alloy having the composition defined in any one of
claims 2-6, 16, and 17 at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of 350-500.degree. C. at a
cooling rate of 100.degree. C./h or more, starting hot rolling of
the ingot at the temperature, cold rolling the hot-rolled product,
and subjecting the cold-rolled product to a solution heat treatment
at a temperature of 500.degree. C. or more, and quenching.
19. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 2-6, 16, and 17, the method comprising homogenizing an ingot
of an aluminum alloy having the composition defined in any one of
claims 2-6, 16, and 17 at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 350.degree. C. at a
cooling rate of 100.degree. C./h or more, heating the ingot to a
temperature of 350-500.degree. C. and starting hot rolling of the
ingot, cold rolling the hot-rolled product, and subjecting the
cold-rolled product to a solution heat treatment at a temperature
of 500.degree. C. or more, and quenching.
20. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 2-6, 16, and 17, the method comprising homogenizing an ingot
of an aluminum alloy having the composition defined in any one of
claims 2-6, 16, and 17 at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 350.degree. C. at a
cooling rate of 100.degree. C./h or more, cooling the ingot to room
temperature, heating the ingot to a temperature of 350-500.degree.
C. and starting hot rolling of the ingot, cold rolling the
hot-rolled product, and subjecting the cold-rolled product to a
solution heat treatment at a temperature of 500.degree. C. or more,
and quenching.
21. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 7-9, 16, and 17, the method comprising homogenizing an ingot
of an aluminum alloy having the composition defined in any one of
claims 7-9, 16, and 17 at a temperature of 480.degree. C. or more,
cooling the ingot to a temperature of 300-450.degree. C. at a
cooling rate of 150.degree. C./h or more, starting hot rolling of
the ingot at the temperature, cold rolling the hot-rolled product,
and subjecting the cold-rolled product to a solution heat treatment
at a temperature of 500.degree. C. or more, and quenching.
22. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 7-9, 16, and 17, the method comprising homogenizing an ingot
of an aluminum alloy having the composition defined in any one of
claims 7-9, 16, and 17 at a temperature of 480.degree. C. or more,
cooling the ingot to a temperature of less than 300.degree. C. at a
cooling rate of 150.degree. C./h or more, heating the ingot to a
temperature of 300-450.degree. C. and starting hot rolling of the
ingot, cold rolling the hot-rolled product, and subjecting the
cold-rolled product to a solution heat treatment at a temperature
of 500.degree. C. or more, and quenching.
23. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 7-9, 16, and 17, the method comprising homogenizing an ingot
of an aluminum alloy having the composition defined in any one of
claims 7-9, 16, and 17 at a temperature of 480.degree. C. or more,
cooling the ingot to a temperature of less than 300.degree. C. at a
cooling rate of 150.degree. C./h or more, cooling the ingot to room
temperature, heating the ingot to a temperature of 300-450.degree.
C. and starting hot rolling of the ingot, cold rolling the
hot-rolled product, and subjecting the cold-rolled product to a
solution heat treatment at a temperature of 500.degree. C. or more,
and quenching.
24. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 11 and 13-17, the method comprising homogenizing an ingot of
an aluminum alloy having the composition defined in any one of
claims 11 and 13-17 at a temperature of 450.degree. C. or more,
cooling the ingot to a specific temperature of less than
350.degree. C. at a cooling rate of 100.degree. C./h or more, hot
rolling the ingot at the specific temperature, cold rolling the
hot-rolled product, and subjecting the cold-rolled product to a
solution heat treatment at a temperature of 450.degree. C. or more,
and quenching.
25. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 11 and 13-17, the method comprising homogenizing an ingot of
an aluminum alloy having the composition defined in any one of
claims 11 and 13-17 at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 350.degree. C. at a
cooling rate of 100.degree. C./h or more, heating the ingot to a
temperature of 300-500.degree. C. and starting hot rolling of the
ingot, cold rolling the hot-rolled product, and subjecting the
cold-rolled product to a solution heat treatment at a temperature
of 450.degree. C. or more, and quenching.
26. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 11 and 13-17, the method comprising homogenizing an ingot of
an aluminum alloy having the composition defined in any one of
claims 11 and 13-17 at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 350.degree. C. at a
cooling rate of 100.degree. C./h or more, cooling the ingot to room
temperature, heating the ingot to a temperature of 300-500.degree.
C. and starting hot rolling of the ingot, cold rolling the
hot-rolled product, and subjecting the cold-rolled product to a
solution heat treatment at a temperature of 450.degree. C. or more,
and quenching.
27. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 18-26, wherein the hot rolling is finished at a temperature
of 300.degree. C. or less.
28. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to any one of
claims 18-27, comprising quenching the solution-treated product to
120.degree. C. at a cooling rate of 5.degree. C./s or more, and
subjecting the quenched product to a heat treatment at a
temperature of 40-120.degree. C. for 50 hours or less within 60
minutes after the quenching.
29. A method for producing the aluminum alloy sheet with excellent
formability and paint bake hardenability according to claim 28,
comprising subjecting the heat-treated product to a reversion
treatment at a temperature of 170-230.degree. C. for 60 seconds or
less within seven days after the heat treatment.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aluminum alloy sheet
with excellent formability and paint bake hardenability and
suitable as a material for transportation parts, in particular, as
an automotive outer panel, and a method for producing the same.
BACKGROUND ART
[0002] An automotive outer panel is required to have 1)
formability, 2) shape fixability (shape of the press die is
precisely transferred to the material by press working), 3) dent
resistance, 4) corrosion resistance, 5) surface quality, and the
like. Conventionally, 5000 series (Al--Mg) aluminum alloys and 6000
series (Al--Mg--Si) aluminum alloys have been applied to the
automotive outer panel. The 6000 series aluminum alloy has
attracted attention because high strength is obtained due to
excellent paint bake hardenability, whereby further gage dawn and
weight saving is expected. Therefore, various improvement have been
made on the 6000 series aluminum alloy.
[0003] Among the properties required for the automotive outer
panel, although the shape fixability prefer lower yield strength,
the dent prefer higher yield strength. In order to solve this
problem, press working are carried out lower yield strength for
shape fixability and dent resistance are improved by excellent
paint bake hardenability using 6000 series aluminum alloy (see JP.
5-247610, JP. 5-279822, JP. 6-17208, etc.).
[0004] The 6000 series aluminum alloy has problems relating to the
surface quality after forming, such as occurrence of orange peel
surfaces and ridging marks (long streak-shaped defects occurring in
the rolling direction during plastic working). Surface quality
defects can be solved by adjusting the alloy components, managing
the production conditions, and the like. For example, a method of
preventing formation of coarse precipitates by homogenizing the
alloy at a temperature of 500.degree. C. or more, cooling the
homogenized product to 450-350.degree. C., and starting hot rolling
in this temperature range has been proposed in order to prevent
occurrence of ridging marks (see JP. 7-228956). However, if the
cooling rate is decreased when cooling the homogenized product from
the homogenization temperature of 500.degree. C. or more to the hot
rolling temperature of 450.degree. C., coarse Mg--Si compounds are
formed. This makes it necessary to perform a solution treatment at
a high temperature for a long time in the subsequent step, whereby
production efficiency is decreased.
[0005] In the case of assembling an outer panel an inner panel
material, 180.degree. bending (flat hemming), in which working
conditions are severe since the ratio (R/t) of the center bending
radius (R) to the sheet thickness (t) is small, is performed.
However, since the 6000 series aluminum alloy has inferior
bendability in comparison with the 5000 series aluminum alloy, flat
hemming can not be performed in high press working area.
DISCLOSURE OF THE INVENTION
[0006] The present inventors have examined for further improving
formability, in particular, bendability of the 6000 series aluminum
alloy. As a result, it has been found that bendability of the 6000
series alloy is affected by the precipitation state of Mg--Si
compounds and misorientation of adjacent crystal grains, and also
found that bendability has a correlation with the Lankford value,
and it is necessary to increase anisotropy of the Lankford values
in order to improve bendability. Furthermore, it has been found
that bendability also has a correlation with the intensity ratio
(random ratio) of cube orientation {100} <001>of the texture,
and it is necessary to allow the texture to have a high degree of
integration of cube orientation in order to improve bendability. In
order to obtain the above properties, the present inventors have
found that it is important to optimize the content of Si and Mg
which are major elements of the 6000 series aluminum alloy, and to
optimize the production steps, in particular, to appropriately
control the cooling rate after homogenization of an ingot.
[0007] The present invention has been achieved based on the above
findings. An object of the present invention is to provide an
aluminum alloy sheet having excellent formability which allows flat
hemming, showing no orange peel surfaces and ridging marks after
forming, having excellent paint bake hardenability capable of
solving the problems relating to shape fixability and dent
resistance, and with excellent corrosion resistance, in particular,
filiform corrosion resistance, and a method for producing the
same.
[0008] An aluminum alloy sheet according to the present invention
for achieving the above object is a 6000 series aluminum alloy
sheet, with excellent bendability after a solution treatment and
quenching, and has a minimum inner bending radius of 0.5 mm or less
during 180.degree. bending with 10% pre-stretch, even if the yield
strength is further increased through natural aging. Specific
embodiments of the aluminum alloy sheet are as follows.
[0009] (1) An aluminum alloy sheet comprising 0.5-1.5% of Si and
0.2-1.0% of Mg, with the balance consisting of Al and impurities,
or comprising 0.8-1.2% of Si, 0.4-0.7% of Mg, and 0.1-0.3% of Zn,
with the balance consisting of Al and impurities, in which the
maximum diameter of Mg--Si compounds is 10 .mu.m or less and the
number of Mg--Si compounds having a diameter of 2-10 .mu.m is 1000
per mm.sup.2 or less.
[0010] (2) An aluminum alloy sheet comprising 0.4-1.5% of Si,
0.2-1.2% of Mg, and 0.05-0.3% of Mn, with the balance consisting of
Al and impurities, in which the percentage of crystal grain
boundaries in which misorientation of adjacent crystal grains is
15.degree. or less is 20% or more.
[0011] (3) An aluminum alloy sheet comprising 0.5-2.0% of Si and
0.2-1.5% of Mg, with 0.7Si %+Mg %.ltoreq.2.2%, and Si %-0.58Mg
%.gtoreq.0.1% being satisfied and the balance consisting of Al and
impurities, in which an anisotropy of Lankford values is more than
0.4. The Lankford value r is the ratio of the logarithmic strain
inthedirectionof thewidthof the sheet to the logarithmic strain in
the direction of the thickness of the sheet when applying a
specific amount of tensile deformation, such as 15%, to a tensile
specimen, specifically, r=(logarithmic strain in the sheet width
direction)/(logarithmic strain in the sheet thickness direction).
The anisotropy of Lankford values is (r0+r90-2.times.r45)/2 (r0: r
value of a tensile specimen collected in a direction at 0.degree.
to the rolling direction, r90: r value of a tensile specimen
collected in a direction at 90.degree. to the rolling direction,
and r45: r value of a tensile specimen collected in a direction at
45.degree. to the rolling direction).
[0012] (4) An aluminum alloy sheet comprising 0.5-2.0% of Si and
0.2-1.5% of Mg, with 0.7Si %+Mg %.ltoreq.2.2% being satisfied and
the balance consisting of Al and impurities, inwhich an intensity
ratio of cube orientation of crystallographic texture is 20 or
more.
[0013] Specific embodiments of a method for producing the above
aluminum alloy sheets are as follows.
[0014] (1) A method for producing an aluminum alloy sheet
comprising homogenizing an ingot of an aluminum alloy having the
above composition at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of 350-500.degree. C. at a
cooling rate of 100.degree. C./h or more, starting hot rolling of
the ingot at the temperature, cold rolling the hot-rolled product,
and subjecting the cold-rolled product to a solution heat treatment
at a temperature of 500.degree. C. or more, and quenching.
[0015] (2) A method for producing an aluminum alloy sheet
comprising homogenizing an ingot of an aluminum alloy having the
above composition at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 300.degree. C. at a
cooling rate of 100.degree. C./h or more, heating the ingot to a
temperature of 350-500.degree. C. and starting hot rolling of the
ingot, cold rolling the hot-rolled product, and subjecting the
cold-rolled product to a solution heat treatment at a temperature
of 500.degree. C. or more, and quenching.
[0016] (3) A method for producing an aluminum alloy sheet
comprising homogenizing an ingot of an aluminum alloy having the
above composition at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 300.degree. C. at a
cooling rate of 100< C./h or more, cooling the ingot to room
temperature, heating the ingot to a temperature of 350-500.degree.
C. and starting hot rolling of the ingot, cold rolling the
hot-rolled product, and subjecting the cold-rolled product to a
solution heat treatment at a temperature of 500.degree. C. or more,
and quenching.
[0017] (4) A method for producing an aluminum alloy sheet
comprising homogenizing an ingot of an aluminum alloy having the
above composition at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 350.degree. C. at a
cooling rate of 100.degree. C./h or more, hot rolling the ingot at
the temperature, cold rolling the hot-rolled product, and
subjecting the cold-rolled product to a solution heat treatment at
a temperature of 450.degree. C. or more, and quenching.
[0018] (5) A method for producing an aluminum alloy sheet
comprising homogenizing an ingot of an aluminum alloy having the
above composition at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 350.degree. C. at a
cooling rate of 100.degree. C./h or more, heating the ingot to a
temperature of 300-500.degree. C. and starting hot rolling of the
ingot, cold rolling the hot-rolled product, and subjecting the
cold-rolled product to a solution heat treatment at a temperature
of 450.degree. C. or more, and quenching.
[0019] (6) A method for producing an aluminum alloy sheet
comprising homogenizing an ingot of an aluminum alloy having the
above composition at a temperature of 450.degree. C. or more,
cooling the ingot to a temperature of less than 350.degree. C. at a
cooling rate of 100.degree. C./h or more, cooling the ingot to room
temperature, heating the ingot to a temperature of 300-500.degree.
C. and starting hot rolling of the ingot, cold rolling the
hot-rolled product, and subjecting the cold-rolled product to a
solution heat treatment at a temperature of 450.degree. C. or more,
and quenching.
PREFERRED EMBODYMENTS
[0020] Effects and reasons for limitations of the alloy components
in the Al--Mg--Si alloy sheet of the present invention are
described below.
[0021] Si is necessary to obtain strength and high paint bake
hardenability (BH), and increases strength by forming Mg--Si
compounds. The Si content is preferably 0.5-2.0%. If the Si content
is less than 0.5%, sufficient strength may not be obtained by
heating during baking and formability may be decreased. If the Si
content exceeds 2.0%, formability and shape fixability may be
insufficient due to high yield strength during press working.
Moreover, corrosion resistance may be decreased after painting. The
Si content is more preferably 0.4-1.5%, still more preferably
0.5-1.5%, yet more preferably 0.6-1.3%, and particularly preferably
0.8-1.2%.
[0022] Mg increases strength in the same manner as Si. The Mg
content is preferably 0.2-1.5%. If the Mg content is less than
0.2%, sufficient strength may not be obtained by heating during
baking. If the Mg content exceeds 1.5%, yield strength may remain
high after a solution heat treatment or additional heat treatment,
whereby formability and spring-back properties may be insufficient.
The Mg content is more preferably 0.2-1.2%, still more preferably
0.2-1.0%, yet more preferably 0.3-0.8%, and particularly preferably
0.4-0.7%.
[0023] Si and Mg are preferably added to satisfy the relations
0.7Si %+Mg %.ltoreq.2.2%, and Si %-0.58Mg %.gtoreq.0.1% so that
anisotropy of the Lankford values is more than 0.4 and bendability
is improved. In order to increase the intensity ratio of cube
orientation of the texture to obtain good bendability, Si and Mg
are preferably added to satisfy the relation 0.7Si %+Mg
%.ltoreq.2.2%.
[0024] Zn improves zinc phosphate treatment properties during the
surface treatment. The Zn content is preferably 0.5% or less. If
the Zn content exceeds 0.5%, corrosion resistance may be decreased.
The Zn content is still more preferably 0.1-0.3%.
[0025] Cu improves strength and formability. The Cu content is
preferably 1.0% or less. If the Cu content exceeds 1.0%, corrosion
resistance may be decreased. The Cu content is still more
preferably 0.3-0.8%. If corrosion resistance is an important, the
Cu content is preferably limited to 0.1% or less.
[0026] Mn, Cr, V, and Zr improve strength and refine crystal grains
to prevent occurrence of orange peel surfaces during forming. The
content of Mn, Cr, V, and Zr is preferably 1.0% or less, 0.3% or
less, 0.29% or less, and 0.2% or less, respectively. If the content
of Mn, Cr, V, and Zr exceeds the above upper limits, coarse
intermetallic compounds may be formed, whereby formability may be
decreased. The content of Mn and Zr is more preferably 0.3% or less
and 0.15% or less, respectively. The content of Mn, Cr, V, and Zr
is still more preferably 0.05-0.3%, 0.05-0.15%, 0.05-0.15%, and
0.05-0.15%, respectively.
[0027] In order to improve bendability by allowing percentage of
crystal grain boundaries in which misorientation of adjacent
crystal grains is 15.degree. or less to be 20% or more, Mn is added
in an amount of 0.05-0.3% as an essential component.
[0028] Ti and B refine a cast structure to improve formability. The
content of Ti and B is preferably 0.1% or less and 50 ppm or less,
respectively. If the content of Ti and B exceeds the above upper
limits, the number of coarse intermetallic compounds may be
increased, whereby formability may be decreased. It is preferable
to limit the Fe content to 0.5% or less, and preferably 0.3% or
less as another impurity.
[0029] The production steps of the aluminum alloy sheet of the
present invention are described below.
[0030] Homogenization condition: Homogenization must be performed
at a temperature of 450.degree. C. or more. If the homogenization
temperature is less than 450.degree. C., removal of ingot
segregation and homogenization may be insufficient. This results in
insufficient dissolution of Mg.sub.2Si components which contribute
to strength, whereby formability may be decreased. Homogenization
is preferably performed at a temperature of 480.degree. C. or
more.
[0031] Cooling after homogenization: Good properties are obtained
by cooling the homogenized product at a cooling rate of preferably
100.degree. C./h or more, and still more preferably 300.degree.
C./h or more. Since large-scale equipment is necessary for
increasing the cooling rate, it is preferable to manage the cooling
rate in the range of 300-1000.degree. C./h in practice. If the
cooling rate is low, Mg--Si compounds are precipitated and
coarsened. In a conventional cooling method, the cooling rate is
about 30.degree. C./h in the case of cooling a large slab. However,
Mg--Si compounds are precipitated and coarsened during cooling at
such a low cooling rate, whereby the material may not be provided
with improved bendability after the solution heat treatment and
quenching.
[0032] If the cooling rate is controlled in this manner, (1)
appropriate distributions of Mg--Si compounds are obtained, (2) the
percentage of crystal grain boundaries in which misorientation of
adjacent crystal grains is 15.degree. or less becomes 20% or more,
(3) anisotropy of Lankford values is increased, and (4) the degree
of integration of cube orientation is increased, whereby
bendability is improved.
[0033] The cooling after homogenization must allow the temperature
to be decreased to less than 350.degree. C., and preferably less
than 300.degree. C. at a cooling rate of 100.degree. C./h or more,
preferably 150.degree. C./h or more, and still more preferably at
300.degree. C./h or more. The properties are affected if a region
at 350.degree. C. or more is partially present. Therefore, an ingot
is cooled until the entire ingot is at 300.degree. C. or less, and
preferably 250.degree. C. or less at the above cooling rate. There
are no specific limitations to the method of cooling the
homogenized ingot insofar as the necessary cooling rate is
obtained. For example, water-cooling, fan cooling, mist cooling, or
heat sink contact may be employed as the cooling method.
[0034] The cooling start temperature is not necessarily the
homogenization temperature. The same effect can be obtained by
allowing the ingot to be cooled to a temperature at which
precipitation does not significantly occur, and starting cooling at
a cooling rate of 100.degree. C./h or more. For example, in the
case where homogenization is performed at a temperature of
500.degree. C. or more, the ingot may be slowly cooled to
500.degree. C.
[0035] Hot rolling: The ingot is cooled to a specific temperature
of 350-500.degree. C. or 300-450.degree. C. from the homogenization
temperature, and hot rolling is started at the specific
temperature. The ingot may be cooled to a specific temperature of
350.degree. C. or less from the homogenization temperature, and hot
rolling may be started at the specific temperature.
[0036] The ingot may be cooled to a temperature of 350.degree. C.
or less and heated to a temperature of 300-500.degree. C., and hot
rolling may be started at this temperature. The ingot may be cooled
to a temperature of 350.degree. C. or less, cooled to room
temperature, heated to a temperature of 300-500.degree. C., and
hot-rolled at this temperature.
[0037] If the hot rolling start temperature is less than
300.degree. C., deformation resistance is increased, whereby
rolling efficiency is decreased. If the hot rolling start
temperature exceeds 500.degree. C., crystal grains coarsen during
rolling, whereby ridging marks readily occur in the resulting
material. Therefore, it is preferable to limit the hot rolling
start temperature to 300-500.degree. C. The hot rolling start
temperature is still more preferably 380-450.degree. C. taking into
consideration deformation resistance and uniform
microstructure.
[0038] The hot rolling finish temperature is preferably 300.degree.
C. or less. If the hot rolling finish temperature exceeds
300.degree. C., precipitation of Mg--Si compounds easily occurs,
whereby formability may be decreased. Moreover, recrystallized
grains coarsen, thereby resulting in occurrence of ridging marks.
Hot rolling is preferably finished at 200.degree. C. or more taking
into consideration deformation resistance during hot rolling and
residual oil stains due to a coolant.
[0039] Cold rolling: The hot rolled sheet is cold rolled to the
final gage.
[0040] Solution heat treatment: The solution heat treatment
temperature is preferably 450.degree. C. or more, and still more
preferably 500.degree. C. or more. If the solution heat treatment
temperature is less than 500.degree. C., dissolution of Mg--Si
precipitates may be insufficient, whereby sufficient strength and
formability cannot be obtained, or heat treatment for a
considerably long time is needed to obtain necessary strength and
formability. This is disadvantageous from the industrial point of
view. There are no specific limitations to the solution heat
treatment time insofar as necessary strength is obtained. The
solution heat treatment time is usually 120 seconds or less from
the industrial point of view.
[0041] Cooling rate during quenching: It is necessary to cool the
sheet from the solution treatment temperature to 120.degree. C. or
less at a cooling rate of 5.degree. C./s or more. It is preferable
to cool the sheet at a cooling rate of 10.degree. C./s or more. If
the quenching cooling rate is too low, precipitation of eluted
elements occurs, whereby strength, BH, formability, and corrosion
resistance may be decreased.
[0042] Additional heat treatment: this heat treatment is performed
at40-120.degree. C. for 50 hours or less within 60 minutes after
quenching. BH is improved by this treatment. If the temperature is
less than 40.degree. C., improvement of BH is insufficient. If the
temperature exceeds 120.degree. C. or the time exceeds 50 hours,
the initial yield strength is excessively increased, whereby
formability or paint bake hardenability is decreased.
[0043] Reversion treatment may be performed at a temperature of
170-230.degree. C. for 60 seconds or less within seven days after
final additional heat treatment. Paint bake harden ability is
further improved by the reversion treatment.
[0044] A sheet material with excellent bendability after the
solution heat treatment and quenching can be obtained by applying
the above production steps to an aluminum alloy having the above
composition. The aluminum alloy sheet is suitably used as a
lightweight automotive member having a complicated shape which is
subjected to hemming, such as a hood, trunk lid, and door.
Moreover, in the case where the aluminum alloy sheet is applied to
a fender, roof, and the like, which are not subjected to hemming,
the aluminum alloy sheet can be subjected to severe working in
which the bending radius is small due to its excellent bendability
after pressing the sheet into a complicated shape. Therefore, the
aluminum alloy sheet widens the range of application of aluminum
materials to automotive materials, thereby contributing to a
decrease in the weight of vehicles.
[0045] In order to securely improve formability, in particular,
bendability, it is preferable to adjust the amount of alloy
components, such as Si and Mg, and production conditions so that
anisotropy of the Lankford values is 0.6 or more and the intensity
ratio of cube orientation of the texture is 50 or more.
[0046] The present invention is described below by comparing
examples of the present invention with comparative examples. The
effects of the present invention will be demonstrated based on this
comparison. The examples illustrate only one preferred embodiment
of the present invention, which should not be construed as limiting
the present invention.
EXAMPLE 1
[0047] Aluminum alloys having compositions shown in Table 1 were
cast by using a DC casting method. The resulting ingots were
homogenized at 540.degree. C. for six hours and cooled to room
temperature at a cooling rate of 300.degree. C./h. The cooled
ingots were heated to a temperature of 400.degree. C., and hot
rolling was started at this temperature. The ingots were rolled to
a thickness of 4.0 mm, and cold-rolled to a thickness of 1.0
mm.
[0048] The cold-rolled sheets were subjected to a solution heat
treatment at 540.degree. C. for five seconds, quenched to a
temperature of 120.degree. C. at a cooling rate of 30.degree. C./s,
and additional heat treated at 100.degree. C. for three hours after
five minutes.
[0049] The final heat treated sheets were used as test materials.
Tensile properties, formability, corrosion resistance, and bake
hardenability were evaluated when 10 days were passed after the
final heat treatment, and the maximum diameter of Mg--Si compounds
and the number of compounds having a diameter of 2-10 .mu.m were
measured according to the following methods. The tensile properties
and a minimum bending radius for formability were also evaluated
when four months were passed after the final heat treatment. The
results are shown in Tables 2 and 3.
[0050] Tensile property: Tensile strength (.sigma..sub.B), yield
strength (.sigma..sub.0.2), and elongation (.delta.) were measured
by performing a tensile test.
[0051] Formability: An Erichsen test (EV) was performed. A test
material having a forming height of less than 10 mm was rejected. A
180.degree. bending test for measuring the minimum bending radius
after applying 10% tensile pre-strain was performed in order to
evaluate hem workability. A test material having a minimum inner
bending radius of 0.5 mm or less was accepted.
[0052] Corrosion resistance: The test material was subjected to a
zinc phosphate treatment and electrodeposition coating using
commercially available chemical treatment solutions. After painting
crosscuts reaching the aluminum base material, a salt spray test
was performed for 24 hours according to JIS Z2371. After allowing
the test material to stand in a wet atmosphere at 50.degree. C. and
95% for one month, the maximum length of filiform corrosion
occurring from the crosscuts was measured. A test material having a
maximum length of filiform corrosion of 4 mm or less was
accepted.
[0053] Bake hardenability (BH): Yield strength (.sigma.0.2) was
measured after applying 2% tensile deformation and performing heat
treatment at 170.degree. C. for 20 minutes. A test material having
a yield strength of 200 MPa or more was accepted.
[0054] Measurement of Mg--Si compound: The maximum diameter of
Mg--Si compounds was measured by observation using an optical
microscope. The distribution of compounds having a diameter of 2-10
.mu.m was examined using an image analyzer in the range of 1 square
millimeter (1 mm.sup.2) in total provided that one pixel=0.25
.mu.m. The Mg--Si compounds were distinguished from Al--Fe
compounds by light and shade of the compounds. The detection
conditions were selected at a level at which only the Mg--Si
compounds were detected by confirming the compound particles in
advance by point analysis.
1 TABLE 1 Composition (mass %) Alloy Si Mg Cu Mn Cr V Zr Fe Zn Ti B
1 1.0 0.5 -- -- -- -- -- 0.17 0.02 0.02 5 2 0.8 0.6 0.02 0.08 -- --
-- 0.17 0.02 0.02 5 3 1.1 0.5 0.01 0.08 -- -- -- 0.17 0.02 0.02 5 4
1.0 0.6 0.7 0.1 -- -- -- 0.17 0.02 0.02 5 5 1.2 0.4 0.01 -- 0.1 --
-- 0.17 0.02 0.02 5 6 1.1 0.5 0.01 0.15 -- 0.12 -- 0.13 0.04 0.02 5
7 1.1 0.5 0.4 0.07 -- -- 0.08 0.15 0.03 0.02 5 Note: Unit for B is
ppm.
[0055]
2 TABLE 2 Formability Corrosion BH Minimum resistance
.sigma..sub.0.2 Test Tensile properties inner Maximum length after
mate- .sigma..sub.B .sigma..sub.0.2 .delta. EV bending of filiform
BH rial Alloy (MPa) (MPa) (%) (mm) radius (mm) corrosion (mm) (MPa)
1 1 242 125 31 10.8 0.1 0 211 2 2 245 131 30 10.4 0.2 1.5 220 3 3
243 127 32 10.6 0.1 0.5 214 4 4 274 134 31 10.5 0.2 3.5 221 5 5 257
135 32 10.6 0.2 1.0 217 6 6 259 132 30 10.2 0.3 1.0 208 7 7 268 136
30 10.3 0.2 2.5 223
[0056]
3 TABLE 3 Properties after Number of natural aging Maximum
compounds for 4 months diameter with Minimum Test of Mg--Si
diameter inner mate- compound of 2-10 .mu.m .sigma..sub.0.2 bending
rial Alloy (.mu.m) (/mm.sup.2) (MPa) radius (mm) 1 1 6 550 143 0.2
2 2 8 800 147 0.3 3 3 6 650 142 0.2 4 4 9 720 150 0.3 5 5 5 580 152
0.4 6 6 5 520 151 0.4 7 7 6 600 155 0.3
[0057] As shown in Tables 2 and 3, test materials Nos. 1 to 7
according to The present invention showed excellent BH of more than
200 MPa in the BH evaluation. The test materials Nos. 1 to 7 had
excellent formability in which the forming height (EV) was more
than 10 mm and the minimum inner bending radius was 0.5 mm or less.
The test materials Nos. 1 to 7 exhibited excellent corrosion
resistance in which the maximum length of filiform corrosion was 4
mm or less.
COMPARATIVE EXAMPLE 1
[0058] Aluminum alloys having compositions shown in Table 4 were
cast by using a DC casting method. The resulting ingots were
treated by the same steps as in Example 1 to obtain cold-rolled
sheets with a thickness of 1 mm. The cold-rolled sheets were
subjected to a solution heat treatment and quenching under the same
conditions as in Example 1, and heat treatment at 100.degree. C.
for three hours after five minutes.
[0059] The final heat treated sheets were used as test materials.
Tensile properties, formability, corrosion resistance, and bake
hardenability of the test materials were evaluated when 10 days
were passed after final heat treatment, and the maximum diameter of
Mg--Si compounds and the number of compounds having a diameter of
2-10 .mu.m were measured according to the same methods as in
Example 1. The tensile properties and the minimum inner bending
radius for formability evaluation were also evaluated when four
months were passed after the final heat treatment. The results are
shown in Tables 5 and 6.
4 TABLE 4 Composition (mass %) Alloy Si Mg Cu Mn Cr V Zr Fe Zn Ti B
8 0.3 0.6 0.01 0.05 0.01 -- -- 0.2 0.03 0.02 5 9 1.9 0.6 0.01 0.05
0.01 -- -- 0.2 0.03 0.02 5 10 1.1 0.1 0.01 0.05 0.01 -- -- 0.2 0.03
0.02 5 11 1.1 1.4 0.01 0.05 0.01 -- -- 0.2 0.03 0.02 5 12 1.1 0.5
1.5 0.05 0.01 -- -- 0.2 0.03 0.02 5 13 1.1 0.5 0.02 0.5 0.01 -- --
0.2 0.03 0.02 5 14 1.1 0.5 0.02 0.02 0.4 -- -- 0.2 0.03 0.02 5 15
1.1 0.5 0.02 0.02 0.01 0.4 -- 0.2 0.03 0.02 5 16 1.1 0.5 0.02 0.02
0.01 -- 0.3 0.2 0.03 0.02 5 Note: Unit for B is ppm.
[0060]
5 TABLE 5 Corrosion resistance Formability Maximum BH Minimum
length .sigma..sub.0.2 Test Tensile properties inner of filiform
after mate- .sigma..sub.B .sigma..sub.0.2 .delta. EV bending
corrosion BH rial Alloy (MPa) (MPa) (%) (mm) radius (mm) (mm) (MPa)
8 8 163 70 30 10.7 0 0.5 125 9 9 265 139 31 10.5 0.5 1.0 224 10 10
157 65 32 10.8 0 1.5 118 11 11 280 141 29 10.2 0.6 1.0 229 12 12
294 132 30 10.6 0.4 5.0 228 13 13 247 130 28 9.7 0.6 1.0 217 14 14
246 128 29 9.6 0.4 1.0 214 15 15 247 129 28 9.8 0.5 1.0 212 16 16
245 132 27 9.5 0.7 1.5 213
[0061]
6 TABLE 6 Properties after Number of natural aging Maximum
compounds for 4 months diameter with Minimum Test of Mg--Si
diameter inner mate- compound of 2-10 .mu.m .sigma..sub.0.2 bending
rial Alloy (.mu.m) (/mm.sup.2) (MPa) radius (mm) 8 8 4 300 85 0 9 9
15 1350 158 0.7 10 10 3 260 79 0 11 11 18 2430 159 0.7 12 12 9 880
154 0.5 13 13 12 1250 146 0.7 14 14 8 940 143 0.5 15 15 12 1120 146
0.6 16 16 14 1290 148 0.7
[0062] As shown in Tables 5 and 6, test material No. 8 and test
material No. 10 showed insufficient BH due to low Si content and
low Mg content, respectively. Test material No. 9 and test material
No. 11 had insufficient bendability due to high Si content and high
Mg content, respectively. Test material No. 12 had inferior
filiform corrosion resistance due to high Cu content. Test
materials Nos. 13 to 16 had a small forming height (EV) due to high
Mn content, high Cr content, high V content, and high Zr content,
respectively. Moreover, these test materials showed insufficient
bendability.
EXAMPLE 2 AND COMPARATIVE EXAMPLE 2
[0063] Ingots of the alloys Nos. 1 and 3 of Example 1 were
homogenized at 540.degree. C. for eight hours. The ingots were
cooled to the hot rolling temperature after homogenization, and hot
rolling was started at the temperatures shown in Table 7. The
thickness of hot-rolled products was 4.5 mm. The hot-rolled
products were cold-rolled to a thickness of 1 mm, subjected to a
solution heat treatment under the conditions shown in Table 7,
quenched to 120.degree. C. at a cooling rate of 15.degree. C./s,
and additional heat treatment at 90.degree. C. for five hours after
10 minutes. In Example 2 and Comparative Example 2, the ingots were
cooled to the hot rolling temperature after homogenization, and hot
rolling was performed at this temperature.
[0064] The final heat treated sheets were used as test materials.
Tensile properties, formability, corrosion resistance, and bake
hardenability of the test materials were evaluated when 10 days
were passed after final heat treatment, and the maximum diameter of
Mg--Si compounds and the number of compounds having a diameter of
2-10 .parallel.m were measured according to the same methods as in
Example 1. The tensile properties and the minimum bending radius
for formability evaluation were also evaluated when four months
were passed after the final heat treatment. Electro deposition
coating was performed after applying 10% tensile deformation in the
direction at 90.degree. to the rolling direction. The presence or
absence of ridging marks was evaluated with the naked eye.
[0065] The results are shown in Tables 8 and 9.
7TABLE 7 Cooling rate Hot rolling Solution heat after start
treatment Test homogenization temperature condition material Alloy
(.degree. C./h) (.degree. C.) (.degree. C.) - (sec) 17 1 150 370
550 - 3 18 1 800 450 520 - 5 19 3 200 400 530 - 7 20 3 600 440 550
- 5 21 3 2000 470 560 - 3 22 1 30 420 550 - 3 23 1 70 400 550 - 3
24 1 200 550 520 - 7 25 3 150 410 450 - 3 26 3 20 450 520 - 5
[0066]
8 TABLE 8 Corrosion resistance Formability Maximum BH Minimum
Occurrence length of .sigma..sub.0.2 Test Tensile properties inner
of filiform after mate- .sigma..sub.B .sigma..sub.0.2 .delta. EV
bending ridging corrosion BH rial Alloy (MPa) (MPa) (%) (mm) radius
(mm) mark (mm) (MPa) 17 1 243 123 30 10.7 0.1 None 1.0 210 18 1 248
126 31 10.6 0 None 1.5 218 19 3 244 125 31 10.5 0 None 0.5 215 20 3
249 127 30 10.4 0 None 0.5 216 21 3 252 129 31 10.5 0.1 None 0.5
215 22 1 195 80 30 10.8 0 None 1.0 180 23 1 207 92 30 10.7 0 None
1.0 188 24 1 245 127 31 10.5 0.2 Observed 0.5 220 25 3 201 92 32
10.5 0 None 2.0 162 26 3 210 105 31 10.7 0 None 1.5 185
[0067]
9 TABLE 9 Properties after Number of natural aging Maximum
compounds for 4 months diameter with Minimum Test of Mg--Si
diameter inner mate- compound of 2-10 .mu.m .sigma..sub.0.2 bending
rial Alloy (.mu.m) (/mm.sup.2) (MPa) radius (mm) 17 1 8 470 141 0.2
18 1 7 630 143 0.1 19 3 6 570 142 0 20 3 6 660 142 0.1 21 3 6 750
142 0.1 22 1 22 1800 97 0 23 1 17 1520 108 0 24 1 8 1360 146 0.3 25
3 15 2520 106 0 26 3 26 2400 127 0
[0068] As shown in Tables 8 and 9, test materials Nos. 17 to 21
according to the present invention showed excellent tensile
strength, BH, formability, and corrosion resistance, and maintained
excellent bendability after natural aging for four months. Test
materials Nos. 22, 23, and 26 had low tensile strength since the
cooling rate after homogenization was low. Moreover, these test
materials showed insufficient BH. Ridging marks occurred in test
material No. 24 due to grain growth during hot rolling since the
hot rolling temperature was high. Test material No.25 had a low
tensile strength and inferior BH due to a low solution heat
treatment temperature.
EXAMPLE 3 AND COMPARATIVE EXAMPLE 3
[0069] Aluminum alloys having compositions shown in Table 10 were
cast by using a DC casting method. The resulting ingots were
homogenized at 540.degree. C. for six hours and cooled to room
temperature at a cooling rate of 300.degree. C./h. The ingots were
then heated to a temperature of 400.degree. C. Hot rolling was
started at this temperature. The ingots were hot-rolled to a
thickness of 4.0 mm, and cold-rolled to a thickness of 1.0 mm.
[0070] The cold-rolled sheets were subjected to a solution heat
treatment at 540.degree. C. for five seconds, quenched to a
temperature of 120.degree. C. at a cooling rate of 30.degree. C./s,
and additional heat treated at 90.degree. C. for three hours after
five minutes.
[0071] The final heat treated sheets were used as test materials.
Tensile properties, formability, corrosion resistance, and bake
hardenability of the test materials were evaluated when 10 days
were passed after final heat treatment, and the maximum diameter of
Mg--Si compounds and the number of compounds having a diameter of
2-10 .mu.m were measured according to the same methods as in
Example 1. The tensile properties and the minimum bending radius
for formability evaluation were also evaluated when four months
were passed after the final heat treatment. The results are shown
in Tables 11 and 12.
10 TABLE 10 Composition (mass %) Alloy Si Mg Zn Cu Mn Cr V Zr Fe Ti
B 17 1.0 0.5 0.18 -- -- -- -- -- 0.17 0.02 5 18 0.9 0.6 0.28 -- --
-- -- -- 0.17 0.02 5 19 1.1 0.45 0.2 0.01 0.01 -- -- -- 0.14 0.02 5
20 1.0 0.5 0.15 0.03 0.04 0.1 -- -- 0.15 0.02 5 21 1.1 0.6 0.2 0.02
0.03 -- 0.1 -- 0.17 0.02 5 22 1.2 0.7 0.25 0.01 0.05 0.2 -- 0.08
0.14 0.02 5 23 0.3 0.6 0.2 0.02 0.08 -- -- -- 0.16 0.02 5 24 1.6
0.6 0.2 0.02 0.07 -- -- -- 0.16 0.02 5 25 1.1 0.1 0.2 0.01 0.15 --
-- -- 0.16 0.02 5 26 1.1 1.4 0.2 0.01 0.08 -- -- -- 0.16 0.02 5 27
1.1 0.5 0.04 0.02 -- -- -- -- 0.16 0.02 5 28 1.1 0.5 0.6 0.01 0.1
0.1 -- -- 0.16 0.02 5 29 1.1 0.5 0.2 0.02 0.07 -- -- -- 0.5 0.02 5
Note: Unit for B is ppm.
[0072]
11 TABLE 11 Corrosion resistance Formability Maximum BH Minimum
length .sigma..sub.0.2 Test Tensile properties inner of filiform
after mate- .sigma..sub.B .sigma..sub.0.2 .delta. EV bending
corrosion BH rial Alloy (MPa) (MPa) (%) (mm) radius (mm) (mm) (MPa)
27 17 243 124 30 10.8 0 0.5 208 28 18 247 126 30 10.6 0.1 1.5 210
29 19 246 128 31 10.8 0 1.0 213 30 20 247 125 31 10.6 0 1.5 209 31
21 249 127 30 10.6 0.1 1.5 211 32 22 251 129 29 10.5 0.2 1.5 214 33
23 186 75 31 10.8 0 0 149 34 24 254 137 30 10.9 0.3 1.0 216 35 25
182 77 32 11 0 1 172 36 26 280 142 29 10.2 0.6 1.0 229 37 27 245
128 30 10.4 0 2.0 215 38 28 247 132 29 10.6 0 3.0 218 39 29 252 134
28 9.4 0.4 1.5 221
[0073]
12 TABLE 12 Properties after Number of natural aging for Maximum
compounds 4 months diameter with Minimum Test of Mg--Si diameter
inner mate- compound of 2-10 .mu.m .sigma..sub.0.2 bending rial
Alloy (.mu.m) (/mm.sup.2) (MPa) radius (mm) 27 17 8 560 142 0.1 28
18 9 820 144 0.2 29 19 7 540 145 0.1 30 20 8 810 145 0.1 31 21 8
820 144 0.1 32 22 9 830 146 0.2 33 23 6 380 93 0 34 24 12 890 156
0.5 35 25 5 250 94 0 36 26 18 2430 158 0.7 37 27 8 710 144 0.1 38
28 7 860 150 0.2 39 29 8 1140 150 0.5
[0074] As shown in Tables 11 and 12, test materials Nos. 27 to 32
according to the present invention showed excellent BH of more than
200 MPa in the BH evaluation. The test materials Nos. 27 to 32 had
excellent formability in which the forming height (EV) was more
than 10 mm and the minimum inner bending radius was 0.2 mm or less.
The test materials Nos. 27 to 32 exhibited excellent corrosion
resistance in which the maximum length of filiform corrosion was 2
mm or less.
[0075] On the contrary, test material No. 33 and test material No.
35 showed insufficient BH due to low Si content and low Mg content,
respectively. Test material No. 34 and test material No. 36
exhibited insufficient bendability due to high Si content and high
Mg content, respectively. Test materials Nos. 37 and 38 exhibited
inferior filiform corrosion resistance due to low Zn content and
high Zn content, respectively. Test material No.39 had a small
forming height (EV) due to high Fe content. Moreover, the test
material No.39 showed insufficient bendability.
EXAMPLE 4 AND COMPARATIVE EXAMPLE 4
[0076] Ingots of the alloy No.17 of Example 3 were homogenized at
540.degree. C. for five hours. The ingots were cooled and
hot-rolled to a thickness of 5.0 mm under conditions shown in Table
13. The hot-rolled products were cold-rolled to a thickness of 1.0
mm, subjected to a solution heat treatment under conditions shown
in Table 13, quenched to 120.degree. C. at a cooling rate of
150.degree. C./s, and additional heat treated at 80.degree. C. for
two hours after five minutes. In Example 4 and Comparative Example
4, the ingots were cooled to the hot rolling temperature after
homogenization, and hot rolling was started at this
temperature.
[0077] The final heat treated sheets were used as test materials.
Tensile properties, formability, corrosion resistance, and bake
hardenability of the test materials were evaluated when 10 days
were passed after final heat treatment, and the maximum diameter of
Mg--Si compounds and the number of compounds having a diameter of
2-10 .mu.m were measured according to the same methods as in
Example 1. The tensile properties and the minimum bending radius
for formability evaluation were also evaluated when four months
were passed after the final heat treatment. Electrodeposition
coating was performed after applying 10% tensile deformation in the
direction at 90.degree. to the rolling direction. The presence or
absence of ridging marks was evaluated with the naked eye. The
results are shown in Tables 14 and 15.
13TABLE 13 Cooling rate Hot rolling Solution heat after start
treatment Test homogenization temperature condition material Alloy
(.degree. C./h) (.degree. C.) (.degree. C.) - (sec) 40 17 300 400
550 - 5 41 17 200 470 530 - 10 42 17 600 440 540 - 10 43 17 40 450
550 - 5 44 17 300 540 520 - 10 45 17 250 420 450 - 10
[0078]
14 TABLE 14 Corrosion resistance Formability Maximum BH Inner
Occurrence length .sigma..sub.0.2 Test Tensile properties minimum
of of filiform after mate- .sigma..sub.B .sigma..sub.0.2 .delta. EV
bending ridging corrosion BH rial Alloy (MPa) (MPa) (%) (mm) radius
(mm) mark (mm) (MPa) 40 17 245 125 30 10.7 0 None 0.5 207 41 17 240
124 31 10.8 0 None 1.0 208 42 17 247 128 30 10.7 0 None 1.0 207 43
17 205 97 30 10.8 0 None 1.0 175 44 17 248 129 31 10.5 0.1 Observed
0.5 209 45 17 195 84 31 11.0 0 None 0.5 162
[0079]
15 TABLE 15 Properties after Number of natural aging Maximum
compounds for 4 months diameter of with Minimum Test Mg--Si
diameter inner mate- compound of 2-10 .mu.m .sigma..sub.0.2 bending
rial Alloy (.mu.m) (/mm.sup.2) (MPa) radius (mm) 40 17 7 620 141
0.1 41 17 8 750 140 0.1 42 17 7 580 144 0.1 43 17 15 1360 111 0 44
17 7 1550 146 0.2 45 17 18 2420 97 0
[0080] As shown in Tables 14 and 15, test materials Nos. 40 to 42
according to the present invention showed excellent tensile
strength, BH, formability, and corrosion resistance, and maintained
excellent bendability after natural aging for four months. Test
material No. 43 had low tensile strength and insufficient BH since
the cooling rate after homogenization was low. Ridging marks
occurred in test material No. 44due to texture growth during hot
rolling, since the hot rolling temperature was high. Test material
No. 45 had a low tensile strength and inferior BH due to a low
solution treatment temperature.
EXAMPLE 5
[0081] Aluminum alloys having compositions shown in Table 16 were
cast by using a DC casting method. The resulting ingots were
homogenized at 540.degree. C. for six hours and cooled to room
temperature at a cooling rate of 300.degree. C./h. The ingots were
heated to a temperature of 400.degree. C., and hot rolling was
started at this temperature. The ingots were hot-rolled to a
thickness of 4.0 mm, and cold-rolled to a thickness of 1.0 mm.
[0082] The cold-rolled sheets were subjected to a solution heat
treatment at 540.degree. C. for five seconds, quenched to a
temperature of 120.degree. C. at a cooling rate of 30.degree. C./s,
and additional heat treated at 100.degree. C. for three hours after
five minutes.
[0083] The final heat treated sheets were used as test materials.
Tensile properties, formability, corrosion resistance, and bake
hardenability of the test materials were evaluated according to the
same methods as in Example 1 when 10 days were passed after final
heat treatment. In addition, misorientation distributions of
crystal grain boundaries were measured according to the following
method. The results are shown in Table 17.
[0084] Measurement of misorientation distribution of crystal grain
boundaries: The surface of the test material was ground using emery
paper and mirror-ground by electrolytic grinding. The test material
was set in a scanning electron microscope (SEM). The tilt angle
distributions of the crystal grain boundaries were measured by
measuring the crystal grain orientation at a pitch of 10 .mu.m
using an EBSP device installed in the SEM at an observation
magnification of 100 times to calculate the percentage of crystal
grain boundaries at 15.degree. or less.
16 TABLE 16 Composition (mass %) Alloy Si Mg Cu Mn Cr V Zr Fe Zn Ti
B 30 1.0 0.5 -- 0.05 -- -- -- 0.13 0.01 0.02 5 31 0.8 0.6 0.02 0.08
-- -- -- 0.15 0.01 0.03 7 32 1.2 0.4 0.01 0.08 -- -- -- 0.16 0.02
0.02 6 33 1.1 0.5 0.01 0.08 -- -- -- 0.19 0.28 0.02 4 34 1.0 0.5
0.7 0.10 -- -- -- 0.16 0.02 0.03 5 35 1.1 0.4 0.01 0.05 0.10 -- --
0.17 0.02 0.03 6 36 1.1 0.5 0.01 0.15 -- 0.13 -- 0.13 0.04 0.02 5
37 1.1 0.5 0.5 0.07 -- -- 0.08 0.15 0.03 0.02 4 Note: Unit for B is
ppm.
[0085]
17 TABLE 17 Corrosion Percentage resistance of crystal Formability
Maximum BH grain Minimum length .sigma..sub.0.2 Test boundaries
Tensile properties inner of filiform after mate- at 15.degree.
.sigma..sub.B .sigma..sub.0.2 .delta. EV bending corrosion BH rial
Alloy or less (%) (MPa) (MPa) (%) (mm) radius (mm) (mm) (MPa) 46 30
38 242 125 32 10.5 0.1 0 213 47 31 35 247 134 31 10.2 0.2 1.3 222
48 32 42 242 125 32 10.7 0.1 0.4 213 49 33 41 242 126 30 10.5 0.1 0
216 50 34 36 278 139 30 10.4 0.1 3.2 225 51 35 43 261 136 32 10.5
0.2 1.2 218 52 36 46 258 129 29 10.4 0.2 1.1 210 53 37 42 265 135
30 10.5 0.2 2.7 222
[0086] As shown in Table 17, test materials Nos. 46 to 53 according
to the conditions of the present invention showed excellent BH of
more than 200 MPa in the BH evaluation. The test materials Nos. 46
to 53 had excellent formability in which the forming height (EV)
was more than 10 mm and the minimum inner bending radius was 0.2 mm
or less. The test materials Nos. 46 to 53 exhibited excellent
corrosion resistance in which the maximum length of filiform
corrosion was 4 mm or less.
COMPARATIVE EXAMPLE 5
[0087] Aluminum alloys having compositions shown in Table 18 were
cast by using a DC casting method. The resulting ingots were
treated by the same steps as in Example 5 to obtain cold-rolled
sheets with a thickness of 1.0 mm. The cold-rolled sheets were
subjected to a solution heat treatment and quenched under the same
conditions as in Example 1. The quenched products were additional
heat treated at 100.degree. C. for three hours after five
minutes.
[0088] The final heat treated sheets were used as test materials.
Tensile properties, formability, corrosion resistance, and bake
hardenability of the test materials were evaluated when 10 days
were passed after final heat treatment, and misorientation
distributions of crystal grain boundaries were measured according
to the same methods as in Example 5. The results are shown in Table
19.
18 TABLE 18 Composition (mass %) Alloy Si Mg Cu Mn Cr V Zr Fe Zn Ti
B 38 0.3 0.5 0.02 0.06 0.01 -- -- 0.15 0.02 0.03 5 39 1.7 0.5 0.02
0.05 0.01 -- -- 0.14 0.03 0.02 6 40 1.0 0.1 0.02 0.04 0.01 -- --
0.17 0.02 0.03 4 41 1.1 1.5 0.02 0.05 0.01 -- -- 0.16 0.03 0.03 5
42 1.0 0.5 0.02 0.06 0.01 -- -- 0.13 0.6 0.02 4 43 1.1 0.6 1.3 0.05
0.01 -- -- 0.15 0.03 0.02 6 44 1.0 0.5 0.01 0.5 0.01 -- -- 0.17
0.03 0.03 4 45 1.0 0.5 0.01 0.06 0.4 -- -- 0.16 0.02 0.02 5 46 1.1
0.6 0.01 0.05 0.01 0.4 -- 0.14 0.02 0.03 4 47 1.1 0.6 0.01 0.06
0.01 -- 0.23 0.16 0.03 0.02 5 48 1.0 0.6 0.02 0.02 0.01 -- -- 0.14
0.02 0.03 5 Note: Unit for B is ppm.
[0089]
19TABLE 19 Percentage of crystal Corrosion BH grain Formability
resistance .sigma..sub.0.2 boundaries Tensile properties Minimum
inner Maximum length after Test at 15.degree. or .sigma..sub.B
.sigma..sub.0.2 .delta. EV bending radius of filiform BH material
Alloy less (%) (MPa) (MPa) (%) (mm) (mm) corrosion (mm) (MPa) 54 38
27 161 68 29 10.8 0 0.4 123 55 39 42 268 142 31 10.6 0.6 1.1 226 56
40 31 160 68 32 10.7 0 1.6 119 57 41 39 279 140 30 10.2 0.7 1.1 228
58 42 41 248 125 31 10.6 0.2 6.8 220 59 43 35 291 129 29 10.5 0.4
5.5 226 60 44 46 245 128 27 9.5 0.7 0.9 215 61 45 51 244 126 29 9.6
0.8 1.1 213 62 46 48 251 131 28 9.8 0.8 1.0 214 63 47 43 244 130 27
9.5 0.7 1.3 214 64 48 17 243 124 30 10.3 0.8 0.4 210
[0090] As shown in Table 19, test material No. 54 and test material
No. 56 exhibited insufficient BH due to low Si content and low Mg
content, respectively. Test material No.55 and test material No. 57
exhibited insufficient bendability due to high Si content and high
Mg content, respectively. Test material No. 58 and test material
No. 59 showed inferior filiform corrosion resistance due to high Zn
content and high Cu content, respectively. Test materials Nos. 60
to 63 had a small forming height (EV) and insufficient bendability
due to high Mn content, high Cr content, high V content, and high
Zr content, respectively. Test material No. 64 exhibited
insufficient bendability since the percentage of crystal grain
boundaries in which misorientation of adjacent crystal grains was
15.degree. or less was less than 20% due to low Mn content.
EXAMPLE 6
[0091] Ingots of the alloy No. 30 shown in Table 16 used in Example
5 were subjected to homogenization, hot rolling, cold rolling,
solution heat treatment, additional heat treatment, and reversion
treatment under conditions shown in Table 20 to obtain test
materials Nos. 65 to 71. In this example, the ingots were cooled to
the hot rolling temperature after homogenization, and hot rolling
was started at this temperature. Moreover, the homogenization time
was six hours, the thickness of the hot-rolled sheet was 4.0 mm,
the thickness of the cold-rolled sheet was 1.0 mm, and the period
of time between quenching and additional heat treatment was five
minutes. The test material No. 65 was subjected to the reversion
treatment at 200.degree. C. for three seconds after the additional
heat treatment. The reversion treatment was performed when one day
was passed after the additional heat treatment.
[0092] Tensile properties, formability, corrosion resistance, and
bake hardenability of the test materials were evaluated when 10
days were passed after final heat treatment, and misorientation
distributions of crystal grain boundaries were measured according
to the same methods as in Example 5. The results are shown in Table
21. Electrodeposition coating was performed after applying 10%
tensile deformation in the direction at 90.degree. to the rolling
direction. The presence or absence of ridging marks was evaluated
with the naked eye. As a result, occurrence of ridging marks was
not observed at all.
20TABLE 20 Homogenization Solution heat Cooling rate Hot rolling
treatment Additional heat after Start Cooling treatment Test Temp.
homogenization temperature Temp. Time rate Temp. Time material
Alloy (.degree. C.) (.degree. C./h) (.degree. C.) (.degree. C.) (s)
(.degree. C./s) (.degree. C.) (h) 65 30 540 300 400 550 5 30 100 3
66 30 520 300 400 550 5 30 100 3 67 30 540 200 400 550 5 30 100 3
68 30 540 300 450 550 5 30 100 3 69 30 540 300 400 520 30 30 100 3
70 30 540 300 400 550 5 10 100 3 71 30 540 300 400 550 10 30 60
5
[0093]
21TABLE 21 Percentage of crystal Corrosion BH grain Formability
resistance .sigma..sub.0.2 boundaries Tensile properties Minimum
inner Maximum length after Test at 15.degree. or .sigma..sub.B
.sigma..sub.0.2 .delta. EV bending radius of filiform BH material
Alloy less (%) (MPa) (MPa) (%) (mm) (mm) corrosion (mm) (MPa) 65 30
41 237 122 31 10.8 0.1 0.3 226 66 30 47 238 117 30 10.4 0.3 0.6 206
67 30 24 241 124 31 10.7 0.3 0.5 206 68 30 27 245 126 31 10.9 0 0.2
215 69 30 48 235 118 31 10.6 0 0.4 207 70 30 37 239 122 31 10.7 0.2
0.6 208 71 30 35 245 126 31 10.7 0.1 0.2 204
[0094] As shown in Table 21, the test materials Nos. 65 to 71
according to The present invention showed excellent tensile
strength, BH, formability, and corrosion resistance. Moreover,
occurrence of ridging marks was not observed at all.
COMPARATIVE EXAMPLE 6
[0095] Ingots of the alloy No. 30 shown in Table 16 used in Example
5 were subjected to homogenization, hot rolling, cold rolling,
solution heat treatment, additional heat treatment, and reversion
treatment under conditions shown in Table 22 to obtain test
materials Nos. 72 to 80. In this example, the ingots were cooled to
the hot rolling temperature after homogenization, and hot rolling
was started at this temperature. Moreover, the homogenization time
was six hours, the thickness of the hot-rolled sheet was 4.0 mm,
the thickness of the cold-rolled sheet was 1.0 mm, and the period
of time between quenching and additional heat treatment was five
minutes. The test material No. 80 was subjected to the reversion
treatment at 300.degree. C. for 30 seconds. The reversion treatment
was performed when one day was passed after the additional heat
treatment.
[0096] Tensile properties, formability, corrosion resistance, and
bake hardenability of the test materials were evaluated when 10
days were passed after final heat treatment, and misorientation
distributions of crystal grain boundaries were measured according
to the same methods as in Example 5. The results are shown in Table
23. Electrodeposition coating was performed after applying 10%
tensile deformation in the direction at 90.degree. to the rolling
direction. The presence or absence of ridging marks was evaluated
with the naked eye. As a result, occurrence of ridging marks was
observed in the test material No. 74.
22TABLE 22 Homogenization Solution heat Cooling rate Hot rolling
treatment Additional heat after Start Cooling treatment Test Temp.
homogenization temperature Temp. Time rate Temp. Time material
Alloy (.degree. C.) (.degree. C./h) (.degree. C.) (.degree. C.) (s)
(.degree. C./s) (.degree. C.) (h) 72 30 450 300 400 550 5 30 100 3
73 30 540 100 400 560 10 30 100 3 74 30 540 50 400 560 20 30 100 3
75 30 540 300 500 550 5 30 100 3 76 30 540 300 400 470 10 30 100 3
77 30 540 300 400 550 5 1 100 3 78 30 540 300 400 550 5 30 -- -- 79
30 540 300 400 550 5 30 140 72 80 30 540 300 400 550 5 30 100 3
[0097]
23TABLE 23 Percentage of crystal Corrosion BH grain Formability
resistance .sigma..sub.0.2 boundaries Tensile properties Minimum
inner Maximum length after Test at 15.degree. or .sigma..sub.B
.sigma..sub.0.2 .delta. EV bending radius of filiform BH material
Alloy less (%) (MPa) (MPa) (%) (mm) (mm) corrosion (mm) (MPa) 72 30
18 215 102 30 9.3 0.8 1.3 172 73 30 15 225 110 31 10.3 0.7 0.7 195
74 30 11 221 107 31 10.4 0.8 0.8 191 75 30 16 243 127 32 10.6 0.7
0.4 218 76 30 43 209 96 27 9.4 0 1.2 164 77 30 35 213 99 28 9.4 0.7
6.2 183 78 30 32 241 124 31 10.8 0.1 0.3 175 79 30 38 281 165 29
9.6 0.4 0.4 228 80 30 36 181 82 30 9.8 0.2 0.2 153
[0098] As shown in Table 23, the test material No. 72 had low EV
and insufficient bendability due to a low homogenization
temperature. Moreover, the test material No.72 showed inferior BH.
The test materials Nos. 73 and 74 showed insufficient bendability
and inferior BH due to a low cooling rate after homogenization.
Ridging marks occurred in the test material No. 75 due to inferior
bendability since the hot rolling start temperature was high. The
test material No.76 had low strength and low EV due to a low
solution treatment temperature. Moreover, the test material No. 76
had low BH. The test material No. 77 showed insufficient EV,
bendability, and corrosion resistance due to a low quenching rate
after the solution heat treatment. Moreover, the test material No.
77 showed insufficient strength and BH. The test material No. 78
had low BH since additional heat treatment was not performed. The
test material No. 79 had low EV since the additional heat treatment
was performed at a high temperature for a long period of time. The
test material No. 80 had low strength and low BH since the
reversion treatment temperature was high. Moreover, the test
material No. 80 had low EV.
EXAMPLE 7
[0099] Aluminum alloys having compositions shown in Table 24 were
cast by using a DC casting method. The resulting ingots were
homogenized at 550.degree. C. for six hours and cooled to
200.degree. C. at a cooling rate of 600.degree. C./h. The ingots
were cooled to room temperature, heated to 420.degree. C., and
hot-rolled to a thickness of 4.5 mm. The hot rolling finish
temperature was 250.degree. C.
[0100] The hot-rolled products were cold-rolled to a thickness of
1.0 mm. The cold-rolled sheets were subjected to a solution heat
treatment at 540.degree. C. for 20 seconds and quenched to
120.degree. C. at a cooling rate of 30.degree. C./s. The quenched
sheets were additional heat treated at 100.degree. C. for three
hours after three minutes.
[0101] Tensile performance, anisotropy of Lankford values, bake
hardenability (BH), and bendability of the aluminum alloy sheets
were evaluated according to the following methods when 10 days were
passed after the final heat treatment. The results are shown in
Table 25.
[0102] Tensile performance: Tensile specimens were collected in
three directions (at 0.degree., 45.degree., and 90.degree. to the
rolling direction), and subjected to a tensile test to determine
average values of tensile strength, yield strength, and elongation
as the tensile performance.
[0103] Anisotropy of Lankford values: Tensile specimens were
collected in three directions (at 0.degree., 45.degree., and
90.degree. to the rolling direction), and subjected to a tensile
test to determine the Lankford values rat 15% deformation, and to
calculate anisotropy of the Lankford values.
[0104] Bake hardenability (BH): Yield strength was measured after
applying 2% tensile deformation in the rolling direction and
performing heat treatment at 170.degree. C. for 20 minutes. A test
material having a yield strength of 200 MPa or more was
accepted.
[0105] Bendability: A 180.degree. bending test for measuring the
minimum bending radius was performed after applying 15% tensile
prestrain. A test material having a minimum inner bending radius of
0.1 mm or less was accepted.
24 TABLE 24 Composition (wt %) Alloy Si Mg Zn Cu Mn Cr V Zr Fe Ti B
49 1.0 0.65 -- -- -- -- -- -- 0.25 0.03 10 50 1.0 0.48 -- 0.02 0.09
-- -- -- 0.17 0.02 5 51 0.91 0.53 0.18 0.01 0.1 -- -- -- 0.18 0.02
5 52 1.0 0.4 0.02 0.72 0.1 -- -- -- 0.18 0.02 5 53 1.6 0.34 -- --
-- 0.05 -- -- 0.18 0.02 5 54 1.1 0.54 0.02 -- 0.05 -- 0.08 -- 0.13
0.01 7 55 0.8 1.1 0.01 0.02 0.07 -- -- 0.08 0.15 0.02 5 Note: Unit
for B is ppm.
[0106]
25 TABLE 25 Tensile performance Yield Tensile Yield strength
Anisotropy Minimum inner Test strength strength Elongation after BH
of Lankford bending radius material Alloy (MPa) (MPa) (%) (MPa)
values r (mm) 81 49 246 132 30 212 0.66 0.0 82 50 237 122 31 206
0.73 0.0 83 51 241 130 30 210 0.70 0.0 84 52 266 127 31 220 0.45
0.1 85 53 252 141 31 223 0.62 0.1 86 54 239 132 30 219 0.66 0.0 87
55 254 138 29 226 0.57 0.1
[0107] As shown in Table 25, test materials Nos. 81 to 87 according
to the present invention excelled in strength and BH, had
anisotropy of the Lankford values of more than 0.4, and showed
excellent minimum bending properties. Bendability after natural
aging for four months was evaluated. As a result, the test
materials of all the alloys had a minimum bending radius of
0.0.about.0.1.
COMPARATIVE EXAMPLE 7
[0108] Aluminum alloys having compositions shown in Table 26 were
cast by using a DC casting method. The resulting ingots were
treated by the same steps as in Example 7. Tensile performance,
anisotropy of Lankford values, bake hardenability (BH), and
bendability of the aluminum alloy sheets were evaluated according
to the same methods as in Example 7 when 10 days were passed after
the final heat treatment. The results are shown in Table 27.
26 TABLE 26 Composition (wt %) Alloy Si Mg Zn Cu Mn Cr V Zr Fe Ti B
56 0.34 0.6 -- 0.01 0.06 0.01 -- -- 0.2 0.02 5 57 2.4 0.5 -- 0.01
0.06 -- -- -- 0.18 0.02 5 58 1.1 0.14 -- 0.01 -- 0.05 -- -- 0.15
0.02 5 59 0.7 1.4 0.1 0.01 -- 0.05 -- -- 0.15 0.02 5 60 1.7 1.3 --
0.01 0.06 -- -- -- 0.18 0.02 5 61 1.1 0.48 -- 1.5 -- -- -- 0.1 0.18
0.02 5 62 1.1 0.53 -- 0.02 1.2 -- -- -- 0.15 0.02 5 63 1.1 0.53 --
0.03 -- 0.4 -- -- 0.17 0.02 5 64 1.1 0.45 -- 0.02 -- 0.01 0.4 --
0.22 0.02 5 65 1.1 0.61 -- 0.01 -- -- -- 0.3 0.14 0.02 5 Note: Unit
for B is ppm.
[0109]
27 TABLE 27 Tensile performance Yield Tensile Yield strength
Anisotropy Minimum inner Test strength strength Elongation after BH
of Lankford bending radius material Alloy (MPa) (MPa) (%) (MPa)
values r (mm) 88 56 152 83 29 123 0.62 0.0 89 57 263 148 31 231
0.34 0.6 90 58 162 85 30 132 0.62 0.0 91 59 249 138 29 194 0.26 0.6
92 60 270 154 28 230 0.31 0.6 93 61 283 147 30 243 0.38 0.7 94 62
253 141 29 227 0.26 0.6 95 63 242 133 28 218 0.32 0.5 96 64 239 135
29 217 0.22 0.6 97 65 242 141 28 220 0.15 0.7
[0110] As shown in Table 27, test material No. 88 and test material
No. 90 exhibited low strength and insufficient BH due to low Si
content and low Mg content, respectively. Test material No. 89 had
high strength due to high Si content, whereby anisotropy of
Lankford values was decreased and bendability was insufficient Test
material No. 91 had a small anisotropy of Lankford values since the
value for (Si %-0.58Mg %) was smaller than 0.1%, whereby minimum
bendability was insufficient.
[0111] Test material No. 92 had a small anisotropy of Lankford
values since (0.7Si %+Mg %) exceeded 2.2%, whereby bendability was
insufficient. Test materials No. 93 to 97 had a small anisotropy of
Lankford values due to high Cu content, high Mn content, high Cr
content, high V content, and high Zr content, respectively, whereby
bendability was insufficient.
EXAMPLE 8 AND COMPARATIVE EXAMPLE 8
[0112] The alloy No. 50 shown in Table 24 was cast by using a DC
casting method. The resulting ingots were homogenized at
540.degree. C. for 10 hours and cooled to 250.degree. C. at cooling
rates shown in Table 28. The ingots were then cooled to room
temperature. The ingots were heated to the temperatures shown in
Table 28 and hot-rolled to a thickness of 4.2 mm. The hot rolling
finish temperature was 280.degree. C. The hot-rolled products were
cold-rolled to obtain sheets with a thickness of 1.0 mm. only test
material No. 107 was cold-rolled to a thickness of 3.0 mm and
subjected to process annealing at 450.degree. C. for 30
seconds.
[0113] The cold-rolled sheets were subjected to a solution heat
treatment at 550.degree. C. for 10 seconds and quenched to
120.degree. C. at a cooling rate of 30.degree. C./s. The quenched
sheets were additional heat treated at 100.degree. C. for three
hours after three minutes. Tensile performance, anisotropy of
Lankford values, BH, and bendability of the aluminum alloy sheets
obtained by these steps were evaluated according to the same
methods as in Example 7.
[0114] For the evaluation of ridging marks, tensile specimens were
collected in the direction at 90.degree. to the rolling direction
and subjected to 10% tensile deformation and electrodeposition
coating. The presence or absence of ridging marks was then
evaluated. The results are shown in Table 29.
28TABLE 28 Cooling rate after Hot rolling start Condition
homogenization (.degree. C./h) temperature (.degree. C.) a 550 420
b 200 400 c 3000 430 d 480 480 e 480 360 f 380 550 g 3000 530 h 50
400 i 30 520 j 550 420
[0115]
29 TABLE 29 Minimum Tensile performance Yield Anisotropy inner
Tensile Yield strength of bending Test strength strength Elongation
after Lankford radius Occurrence of material Condition (MPa) (MPa)
(%) BH (MPa) values r (mm) ridging mark 98 a 230 121 30 210 0.55
0.0 None 99 b 218 118 31 207 0.62 0.0 None 100 c 234 132 30 226
0.58 0.1 None 101 d 241 130 31 230 0.51 0.1 None 102 e 225 123 32
219 0.67 0.0 None 103 f 236 127 31 227 0.45 0.3 Observed 104 g 238
131 29 222 0.33 0.3 Observed 105 h 212 107 31 193 0.25 0.5 None 106
i 231 125 30 214 0.18 0.6 Observed 107 j 224 118 29 204 0.1 0.4
None
[0116] As shown in Table 29, test materials Nos. 98 to 102
according to The present invention excelled in strength and BH, had
an anisotropy of Lankford values of more than 0.4, and showed
excellent minimum bending properties.
[0117] On the contrary, ridging marks occurred in test materials
Nos. 103 and 104 due to a high hot rolling temperature. Test
material No. 105 had a small anisotropy of Lankford values due to a
low cooling rate after homogenization, whereby bendability was
insufficient. Ridging marks occurred in test material No. 106 due
to a high hot rolling temperature and a low cooling rate after
homogenization. Moreover, the test material No. 106 had a small
anisotropy of Lankford values, whereby bendability was
insufficient. Test material No. 107 had a small anisotropy of
Lankford values since process annealing was performed, whereby
bendability was insufficient.
EXAMPLE 9
[0118] The alloy No. 50 shown in Table 24 was cast by using a DC
casting method. The resulting ingots were homogenized at
550.degree. C. for eight hours and cooled to 200.degree. C. at a
cooling rate of 500.degree. C./h. The ingots were cooled to room
temperature, heated to 400.degree. C., and hot-rolled to a
thickness of 4.2 mm. The hot rolling finish temperature was
260.degree. C.
[0119] The hot-rolled products were cold-rolled to obtain sheets
with a thickness of 1.0 mm. The cold-rolled sheets were subjected
to a solution heat treatment at 550.degree. C. for four seconds and
quenched to 120.degree. C. at a cooling rate of 40.degree. C./s.
The quenched sheets were additional heat treated at 100.degree. C.
for two hours after two minutes.
[0120] The aluminum alloy sheets obtained by these steps were
subjected to measurements of tensile strength, yield strength,
elongation, Lankford value r, yield strength after BH, and minimum
bending radius in the directions at 0.degree., 45.degree., and
90.degree. to the rolling direction by using the same methods as in
Example 7 when seven days were passed after the final heat
treatment. Anisotropy of Lankford values r was calculated and the
presence or absence of ridging marks was evaluated. The results are
shown in Table 30. As shown in Table 30, excellent properties were
obtained in all the directions.
30 TABLE 30 Minimum Tensile performance Yield inner Angle to
Tensile strength Anisotropy bending Occurrence rolling strength
Yield Elongation after BH n r of Lankford radius of ridging
direction (MPa) (MPa) (%) (MPa) value value values r (mm) mark
0.degree. 241 128 23 227 0.26 0.66 0.61 0.0 None 45.degree. 225 112
37 205 0.29 0.18 0.0 None 90.degree. 234 122 30 221 0.27 0.92 0.0
None
EXAMPLE 10
[0121] Aluminum alloys having compositions shown in Table 31 were
cast by using a DC casting method. The resulting ingots were
homogenized at 550.degree. C. for six hours and cooled to
200.degree. C. at a cooling rate of 450.degree. C./h. The ingots
were then cooled to room temperature, heated to 420.degree. C., and
hot-rolled to a thickness of 4.5 mm. The hot rolling finish
temperature was 250.degree. C.
[0122] The hot-rolled products were cold-rolled to obtain sheets
with a thickness of 1.0 mm. The cold-rolled sheets were subjected
to a solution heat treatment at 540.degree. C. for 20 seconds and
quenched to 120.degree. C. at a cooling rate of 30.degree. C./s.
The sheets were additional heat treated at 100.degree. C. for three
hours after three minutes.
[0123] The aluminum alloy sheets were subjected to a tensile test
when 10 days were passed after the final heat treatment. Bake
hardenability (BH), intensity ratio (random ratio) of cube
orientation, and bendability were evaluated according to the
following methods. The results are shown in Table 32.
[0124] Intensity ratio of cube orientation: The intensity ratio of
cube orientation was calculated by a series expansion method
proposed by Bunge using an ODF analysis device in which the
expansion order of even-numbered terms was 22 and the expansion
order of odd-numbered terms was 19.
[0125] Bake hardenability (BH): Yield strength was measured after
applying 2% tensile deformation and performing heat treatment at
170.degree. C. for 20 minutes. A test material having a yield
strength of 200 MPa or more was accepted.
[0126] Bendability: A 180.degree. bending test for measuring the
minimum bending radius was performed after applying 15%
tensileprestrain. A test material having a minimum inner bending
radius of 0.2 mm or less was accepted.
31 TABLE 31 Composition (wt %) Alloy Si Mg Zn Cu Mn Cr V Zr Fe Ti B
66 1.0 0.62 -- -- -- -- -- -- 0.24 0.03 10 67 1.0 0.46 -- 0.01 0.08
-- -- -- 0.16 0.02 5 68 0.94 0.53 0.18 0.01 0.10 -- -- -- 0.15 0.02
5 69 1.0 0.42 0.04 0.75 0.10 -- -- -- 0.15 0.02 5 70 1.6 0.36 -- --
-- 0.06 -- -- 0.15 0.02 5 71 1.1 0.54 0.02 -- 0.05 -- 0.09 -- 0.12
0.01 7 72 0.9 1.1 0.01 0.02 0.07 -- -- 0.07 0.14 0.02 5 Note: Unit
for B is ppm.
[0127]
32TABLE 32 Tensile performance Yield Intensity Tensile Yield
strength ratio of Minimum inner Test strength strength Elongation
after BH cube bending radius material Alloy (MPa) (MPa) (%) (MPa)
orientation (mm) 108 66 244 130 31 208 63 0.1 109 67 238 123 31 207
82 0.0 110 68 239 128 31 212 57 0.1 111 69 263 125 30 222 38 0.2
112 70 252 147 31 226 44 0.2 113 71 241 134 30 221 78 0.1 114 72
253 136 30 228 27 0.2
[0128] As shown in Table 32, test materials Nos.108 to 114
according to The present invention excelled in strength and BH, had
an intensity ratio of cube orientation of more than 20, and showed
excellent minimum bending properties. Bendability after natural
aging for four months was measured. As a result, the test materials
of all the alloys had a minimum bending radius of 0.4 or less
although the yield strength exceeded 160 MPa.
COMPARATIVE EXAMPLE 9
[0129] Aluminum alloys having compositions shown in Table 33 were
cast by using a DC casting method. The resulting ingots were
treated by the same steps as in Example 10. Tensile performance,
bake hardenability (BH), intensity ratio of cube orientation, and
bendability of the aluminum alloy sheets were evaluated according
to the same methods as in Example 10 when 10 days were passed after
the final heat treatment. The results are shown in Table 34.
33 TABLE 33 Composition (wt %) Alloy Si Mg Zn Cu Mn Cr V Zr Fe Ti B
73 0.37 0.62 -- 0.01 0.06 0.01 -- -- 0.22 0.02 5 74 2.4 0.61 --
0.01 0.06 -- -- -- 0.17 0.02 5 75 1.1 0.13 -- 0.01 -- 0.05 -- --
0.14 0.02 5 76 0.7 1.8 0.1 0.01 -- 0.05 -- -- 0.14 0.02 5 77 1.7
0.46 -- 1.5 -- -- -- 0.12 0.17 0.02 5 78 1.1 0.55 -- 0.02 1.3 -- --
-- 0.14 0.02 5 79 1.1 0.54 -- 0.03 -- 0.4 -- -- 0.17 0.02 5 80 1.1
0.47 -- 0.02 -- 0.01 0.4 -- 0.24 0.02 5 81 1.1 0.63 -- 0.01 -- --
-- 0.3 0.13 0.02 5 Note: Unit for B is ppm.
[0130]
34 TABLE 34 Tensile performance Yield Intensity Tensile Yield
strength ratio of Minimum inner Test strength strength Elongation
after BH cube bending radius material Alloy (MPa) (MPa) (%) (MPa)
orientation (mm) 115 73 148 79 30 119 51 0.0 116 74 261 147 31 228
16 0.6 117 75 155 75 29 127 66 0.0 118 76 270 149 29 283 14 0.6 119
77 281 145 29 244 8 0.7 120 78 251 140 29 228 14 0.6 121 79 243 132
27 220 15 0.6 122 80 236 133 29 218 12 0.6 123 81 238 139 29 222 17
0.7
[0131] As shown in Table 34, test material No. 115 and test
material No. 117 had low strength and insufficient BH due to low Si
content and low Mg content, respectively. Test material No. 116 and
test material No. 118 showed high strength since (0.7Si %+Mg %)
exceeded 2.2% due to high Si content and high Mg content,
respectively. As a result, the degree of integration of cube
orientation was decreased, whereby bendability was
insufficient.
[0132] The degree of integration of cube orientation was decreased
in test materials Nos. 119 to 123 due to high Cu content, high Mn
content, high Cr content, high V content, and high Zr content,
respectively, whereby bendability was insufficient.
EXAMPLE 11 AND COMPARATIVE EXAMPLE 10
[0133] The alloy No. 67 shown in Table 31 was cast by using a DC
casting method. The resulting ingots were homogenized at
550.degree. C. for five hours and cooled to 250.degree. C. at a
cooling rate shown in Table 35. The ingots were heated to a
temperature shown in Table 35 and hot-rolled to a thickness of 4.4
mm. The hot rolling finish temperature was 250.degree. C. The
hot-rolled products were cold-rolled to obtain sheets with a
thickness of 1.0 mm. Annealing process was performed at 400.degree.
C. for two hours after hot rolling under a condition "t".
[0134] The sheets were subjected to a solution heat treatment at
550.degree. C. for five seconds and quenched to 120.degree. C. at a
cooling rate of 30.degree. C./s. The quenched sheets were
additional heat treated at 100.degree. C. for three hours after
three minutes. Tensile performance, BH, intensity ratio of cube
orientation, and bendability of the aluminum alloy sheets obtained
by these steps were evaluated according to the same methods as in
Example 10.
[0135] For the evaluation of ridging marks, tensile specimens were
collected in the direction at 90.degree. to the rolling direction
and subjected to 10% tensile deformation and electrodeposition
coating. The presence or absence of ridging marks was then
evaluated.
[0136] The results are shown in Table 36.
35TABLE 35 Cooling rate after Hot rolling start Condition
homogenization (.degree. C./h) temperature (.degree. C.) k 550 420
l 200 430 m 3500 410 n 500 470 o 450 350 p 360 540 q 2000 520 r 50
410 s 25 530 t 500 420
[0137]
36 TABLE 36 Tensile performance Yield Intensity Minimum Occurrence
Tensile Yield strength ratio of inner of Test strength strength
Elongation after BH cube bending radius ridging material Condition
(MPa) (MPa) (%) (MPa) orientation (mm) mark 124 k 232 122 29 213 77
0.0 None 125 l 224 120 31 206 85 0.0 None 126 m 232 131 30 227 73
0.1 None 127 n 241 131 31 232 70 0.1 None 128 o 225 123 31 220 83
0.0 None 129 p 235 126 30 224 35 0.3 Observed 130 q 230 126 28 218
28 0.3 Observed 131 r 214 109 30 190 11 0.5 None 132 s 233 123 30
213 7 0.6 Observed 133 t 226 118 30 208 15 0.4 None
[0138] As shown in Table 36, test materials Nos. 124 to 128
according to The present invention excelled in strength and BH, had
an intensity ratio of cube orientation of more than 20, and showed
excellent minimum bending properties.
[0139] On the contrary, ridging marks occurred in test materials
Nos. 129 and 130 due to a high hot rolling temperature. Test
material No. 131 had a small degree of integration of cube
orientation due to a low cooling rate after homogenization, whereby
bendability was insufficient. Ridging marks occurred in test
material No. 132 due to a high hot rolling temperature and a low
cooling rate after homogenization. Moreover, the test material No.
132 had a small degree of integration of cube orientation, whereby
bendability was insufficient. Test material No. 133 had a small
degree of integration of cube orientation since process annealing
was performed, whereby bendability was insufficient.
Industrial Applicability
[0140] According to The present invention, an aluminum alloy sheet
having excellent bendability which allows flat hemming, excellent
bake hardenability, and excellent corrosion resistance, and a
method for producing the same can be provided. The aluminum alloy
sheet is suitably used as a lightweight automotive member having a
complicated shape which is subjected to hemming, such as an
automotive hood, trunk lid, and door.
* * * * *