U.S. patent application number 15/777798 was filed with the patent office on 2018-12-06 for aluminum alloy material and production method therefor.
The applicant listed for this patent is UACJ CORPORATION. Invention is credited to Hidenori Hatta, Shuhei Shakudo, Taichi Suzuki.
Application Number | 20180347017 15/777798 |
Document ID | / |
Family ID | 58719170 |
Filed Date | 2018-12-06 |
United States Patent
Application |
20180347017 |
Kind Code |
A1 |
Suzuki; Taichi ; et
al. |
December 6, 2018 |
ALUMINUM ALLOY MATERIAL AND PRODUCTION METHOD THEREFOR
Abstract
An aluminum alloy material as one aspect of the present
disclosure has a chemical composition including: Zn: more than 6.5%
(mass %, same applies hereafter) and 8.5% or less; Mg: 0.5% or more
and 1.5% or less; Cu: 0.10% or less; Fe: 0.30% or less; Si: 0.30%
or less; Mn: less than 0.05%; Cr: less than 0.05%; Zr: 0.05% or
more and 0.10% or less; and Ti: 0.001% or more and 0.05% or less, a
balance including Al and inevitable impurities. In the aluminum
alloy material, a mass ratio of Zn to Mg (Zn/Mg) is 5 or more and
16 or less, and a metallographic structure includes an equigranular
recrystallized structure.
Inventors: |
Suzuki; Taichi; (Tokyo,
JP) ; Hatta; Hidenori; (Tokyo, JP) ; Shakudo;
Shuhei; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UACJ CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
58719170 |
Appl. No.: |
15/777798 |
Filed: |
November 18, 2016 |
PCT Filed: |
November 18, 2016 |
PCT NO: |
PCT/JP2016/084338 |
371 Date: |
May 21, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/04 20130101; C22F
1/00 20130101; C22F 1/053 20130101; C22C 21/00 20130101; C22C 21/10
20130101 |
International
Class: |
C22C 21/10 20060101
C22C021/10; C22F 1/053 20060101 C22F001/053 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 20, 2015 |
JP |
2015-227926 |
Claims
1. An aluminum alloy material having a chemical composition
comprising: Zn: more than 6.5% (mass %, same applies hereafter) and
8.5% or less; Mg: 0.5% or more and 1.5% or less; Cu: 0.10% or less;
Fe: 0.30% or less; Si: 0.30% or less; Mn: less than 0.05%; Cr: less
than 0.05%; Zr: 0.05% or more and 0.10% or less; and Ti: 0.001% or
more and 0.05% or less, a balance comprising Al and inevitable
impurities, wherein a mass ratio of Zn to Mg (Zn/Mg) is 5 or more
and 16 or less, and wherein a metallographic structure comprises a
recrystallized structure, which is equigranular.
2. The aluminum alloy material according to claim 1, wherein the
recrystallized structure comprises crystal grains having an average
grain diameter of 500 .mu.m or less in a cross-section parallel to
a direction orthogonal to a working direction, and a difference
between a maximum value and a minimum value of grain diameters of
the crystal grains is less than 300 .mu.m.
3. A production method for an aluminum alloy material, a
metallographic structure of which comprises an equigranular
recrystallized structure, the method comprising: preparing an ingot
having a chemical composition comprising: Zn: more than 6.5% (mass
%, same applies hereafter) and 8.5% or less; Mg: 0.5% or more and
1.5% or less; Cu: 0.10% or less; Fe: 0.30% or less; Si: 0.30% or
less; Mn: less than 0.05%; Cr: less than 0.05%; Zr: 0.05% or more
and 0.10% or less; and Ti: 0.001% or more and 0.05% or less, a
balance comprising Al and inevitable impurities, wherein a mass
ratio of Zn to Mg (Zn/Mg) is 5 or more and 16 or less; and
performing a homogenizing treatment in which the ingot is heated at
a temperature higher than 540.degree. C. and 580.degree. C. or
lower for 1 hour or longer and 24 hours or shorter.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This international application claims the benefit of
Japanese Patent Application No. 2015-227926 filed on Nov. 20, 2015
with the Japan Patent Office, and the entire disclosure of Japanese
Patent Application No. 2015-227926 is incorporated herein.
TECHNICAL FIELD
[0002] The present disclosure relates to an aluminum alloy material
and a production method therefor.
BACKGROUND ART
[0003] Conventional 7000-series aluminum alloys with Zn and Mg
added to Al have been known as aluminum alloys exhibiting a high
strength. Such 7000-series aluminum alloys exhibit a high strength
due to age precipitation of Al--Mg--Zn-based fine precipitates.
7000-series aluminum alloys to which Cu has been added in addition
to Zn and Mg exhibit the highest strength among aluminum
alloys.
[0004] 7000-series aluminum alloys are produced by, for example,
hot extrusion or other process, and are used in applications
requiring a high strength, including transportation equipment, such
as aircraft and vehicles, and machine parts, as well as sporting
goods and so on. Properties that 7000-series aluminum alloys are
required to have when used in such applications include impact
absorbability (toughness), resistance to stress corrosion cracking
(hereinafter referred to as resistance to SCC, which is an
abbreviation of Stress Corrosion Cracking), and so on, in addition
to strength. Proposed as an example of 7000-series aluminum alloys
is, for example, an aluminum alloy extruded material disclosed in
Patent Document 1.
PRIOR ART DOCUMENTS
Patent Documents
[0005] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2007-119904
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0006] In 7000-series aluminum alloys, when an amount of Zn and Mg
added to achieve a high strength is increased, a strength improving
effect is obtained, whereas a problem of decrease in workability,
such as extrusion processability, arises.
[0007] Further, in the above-described applications, good
appearance properties are required in addition to the
above-described various properties; thus, surface quality such as
surface texture and visual appearance is regarded as important. In
general 7000-series aluminum alloys, when a surface treatment such
as anodization is performed for the purpose of preventing surface
scratches, compounds precipitated on a grain boundary are
preferentially etched at pretreatment, whereby streak patterns or
the like are generated on the surface-treated surface, resulting in
a problem in surface quality. Especially in a case where the
metallographic structure is made to be fibrous in order to obtain a
higher strength, such streak patterns are conspicuous because the
compounds precipitated on the grain boundary are arranged along the
fibrous metallographic structure. As a result, it is difficult to
obtain a good surface quality.
[0008] Means for solving the above-described problems in surface
quality, such as generation of the streak patterns, include to make
the metallographic structure to be a recrystallized structure,
which is not fibrous but equigranular. With such a recrystallized
structure, a situation can be inhibited in which the compounds
precipitated on the grain boundary are arranged linearly, whereby
generation of streak patterns can be reduced. However, it is known
that, in the case where a 7000-series aluminum alloy has the
recrystallized structure, its strength is lowered and its toughness
and resistance to SCC are also decreased in some cases, as compared
with the case of having the fibrous structure. In addition, with
the recrystallized structure, scale-like patterns are conspicuous
although generation of the streak patterns can be reduced. In this
way, conventional 7000-series aluminum alloys have been difficult
to use in the applications requiring properties such as resistance
to SCC and surface quality as well, in addition to a high strength
and a high toughness.
[0009] In one aspect of the present disclosure, it is desirable to
provide a high-strength aluminum alloy material that is excellent
in surface quality, toughness, and resistance to SCC; and a
production method therefor.
Means for Solving the Problems
[0010] An aluminum alloy material as one aspect of the present
disclosure has a chemical composition comprising: Zn: more than
6.5% (mass %, same applies hereafter) and 8.5% or less; Mg: 0.5% or
more and 1.5% or less; Cu: 0.10% or less; Fe: 0.30% or less; Si:
0.30% or less; Mn: less than 0.05%; Cr: less than 0.05%; Zr: 0.05%
or more and 0.10% or less; and Ti: 0.001% or more and 0.05% or
less, a balance comprising Al and inevitable impurities. In the
aluminum alloy material, a mass ratio of Zn to Mg (Zn/Mg) is 5 or
more and 16 or less, and a metallographic structure comprises an
equigranular recrystallized structure.
[0011] The above-described aluminum alloy material has the
above-specified chemical composition, and its metallographic
structure comprises the equigranular recrystallized structure. This
makes it possible to inhibit poor surface quality after surface
treatment such as anodization, as compared with a case in which its
metallographic structure is a fibrous structure. In particular,
regulation of the upper limit of the Mg content makes it possible
to inhibit precipitation of the compounds on the grain boundary
while ensuring a high strength, thereby inhibiting generation of
scale-like patterns on the surface caused by the recrystallized
structure after surface treatment such as anodization. Moreover,
regulation of the upper limit of the Cu content makes it possible
to inhibit the surface from becoming yellowish in color tone by
surface treatment. As a result, a good surface quality can be
obtained. Furthermore, by setting the mass ratio of Zn to Mg
(Zn/Mg) to the above-specified range, toughness and resistance to
SCC can be improved while ensuring a high strength.
[0012] A production method for an aluminum alloy material as
another aspect of the present disclosure is a method for producing
an aluminum alloy material, a metallographic structure of which
comprises an equigranular recrystallized structure. The method
comprises: preparing an ingot having a chemical composition
comprising: Zn: more than 6.5% (mass %, same applies hereafter) and
8.5% or less; Mg: 0.5% or more and 1.5% or less; Cu: 0.10% or less;
Fe: 0.30% or less; Si: 0.30% or less; Mn: less than 0.05%; Cr: less
than 0.05%; Zr: 0.05% or more and 0.10% or less; and Ti: 0.001% or
more and 0.05% or less, a balance comprising Al and inevitable
impurities, wherein a mass ratio of Zn to Mg (Zn/Mg) is 5 or more
and 16 or less; and performing a homogenizing treatment in which
the ingot is heated at a temperature higher than 540.degree. C. and
580.degree. C. or lower for 1 hour or longer and 24 hours or
shorter.
[0013] In the above-described production method for the aluminum
alloy material, the ingot having the above-specified chemical
component and having the mass ratio of Zn to Mg (Zn/Mg) set to the
above-specified range is prepared in the production process. Then,
the ingot is subjected to the homogenizing treatment under the
above-specified conditions. In particular, by setting the heating
temperature in the homogenizing treatment to a high temperature,
which is higher than 540.degree. C. and 580.degree. C. or lower, it
becomes possible to easily obtain the above-described aluminum
alloy material, that is, a high-strength aluminum alloy material, a
metallographic structure of which comprises an equigranular
recrystallized structure and which is excellent in surface quality,
toughness, and resistance to SCC.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is an explanatory diagram showing a bending test
method.
[0015] FIG. 2 is an explanatory diagram showing a method for
observing metallographic structures.
EXPLANATION OF REFERENCE NUMERALS
[0016] 10 . . . test piece, 20 . . . specimen
MODE FOR CARRYING OUT THE INVENTION
[0017] Embodiments of the present disclosure will be described
below. It is needless to say that the present disclosure is not
limited to the below-described embodiments, and that the present
disclosure can be practiced in various forms within the scope not
departing from the gist of the present disclosure.
[0018] Detailed explanation will be given of a composition of
respective components of aluminum alloy materials in the
embodiments of the present disclosure.
[0019] Zn:
[0020] Zn coexists with Mg to precipitate a .eta.' phase, and
provides an effect of improving strength. The range of Zn content
is more than 6.5% and 8.5% or less. If the Zn content is 6.5% or
less, a precipitation amount of the .eta.' phase is reduced, thus
decreasing the strength improving effect. In contrast, if the Zn
content is more than 8.5%, hot workability is reduced to thereby
decrease productivity. A preferred range of the Zn content is 7.0%
or more and 8.0% or less.
[0021] Mg:
[0022] Mg coexists with Zn to precipitate a .eta.' phase, and
provides the effect of improving strength. The range of Mg content
is 0.5% or more and 1.5% or less. In particular, by regulating the
upper limit of the Mg content to 1.5% or less, it is possible to
inhibit precipitation of compounds on a grain boundary (a crystal
grain boundary, a sub-grain boundary, or the like), while obtaining
the strength improving effect. This makes it possible to reduce, at
the time of surface treatment such as anodization, an amount of the
compounds that have precipitated on the grain boundary to be etched
at pretreatment, to thereby inhibit generation of scale-like
patterns on the surface-treated surface.
[0023] If the Mg content is less than 0.5%, a precipitation amount
of the .eta.' phase is reduced, thus decreasing the strength
improving effect. In contrast, if the Mg content is more than 1.5%,
coarse compounds are likely to be generated on the grain boundary,
thus increasing an amount of the compounds to be etched at
pretreatment of surface treatment such as anodization. Therefore,
scale-like patterns are generated on the surface-treated surface,
resulting in poor surface quality. To obtain a good surface quality
and a higher strength, the Mg content is preferably 1.0% or more
and 1.3% or less.
[0024] Cu:
[0025] Cu may get mixed in when a recycled material is used as a
raw material for an aluminum alloy material. In a 7000-series
aluminum alloy, inclusion of Cu contributes to improvement in
strength, whereas change in color tone or the like occurs, such as
yellowing of the color tone of the surface caused by surface
treatment such as anodization. Such change in color tone may cause
poor surface quality. Thus, when an emphasis is particularly placed
on the color tone of the surface-treated surface, the upper limit
of Cu content needs to be regulated. Regulation of the upper limit
of the Cu content to 0.10% or less makes it possible to reduce the
above-described poor surface quality. The Cu content is preferably
0.08% or less.
[0026] Fe, Si, Mn, and Cr:
[0027] Fe and Si may get mixed in as impurities of aluminum metal.
Mn and Cr may get mixed in when a recycled material is used as a
raw material for an aluminum alloy material. Of the above-described
four components, Fe, Si, and Mn have an effect of inhibiting
recrystallization by forming Al--Mn-based, Al--Mn--Fe-based, and/or
Al--Mn--Fe--Si-based intermetallic compounds in combination with
Al. Cr has an effect of inhibiting recrystallization by forming
Al--Cr-based intermetallic compounds in combination with Al. Thus,
inclusion of the above-described four components results in
inhibiting formation of a recrystallized structure, and instead
results in formation of a fibrous structure.
[0028] That is, excessive inclusion of the above-described four
components results in formation of the fibrous structure and, in
combination with the size and distribution of the compounds, streak
patterns are generated on the surface subjected to surface
treatment such as anodization, leading to poor surface quality.
Thus, by regulating Fe content to 0.30% or less, Si content to
0.30% or less, Mn content to less than 0.05%, and Cr content to
less than 0.05%, formation of the fibrous structure is inhibited,
and the above-described poor surface quality, specifically
generation of the streak patterns, can thereby be inhibited.
[0029] Zr:
[0030] Zr is added to obtain a fine and uniform recrystallized
structure. The range of Zr content is 0.05% or more and 0.10% or
less. Zr forms fine Al--Zr-based compounds in combination with Al.
In the process of producing the aluminum alloy material, the
crystal structure of the Al--Zr-based compounds changes depending
on the temperature at which the ingot is subjected to homogenizing
treatment. If the temperature in the homogenizing treatment is
540.degree. C. or lower, a metastable phase is formed which has an
L1.sub.2 structure commensurate with the matrix, thus inhibiting
recrystallization in the structure subjected to hot working and
readily leading to formation of a fibrous structure. In contrast,
if the homogenizing treatment is performed at a temperature higher
than 540.degree. C. and 580.degree. C. or lower, the Al--Zr-based
compounds change into an equilibrium phase having a D0.sub.23
structure. This results in formation of an equigranular
recrystallized structure, not a fibrous structure, after hot
working, and also inhibits recrystallized grains from coarsening by
blocking movement of the crystal grain boundary.
[0031] If the Zr content is less than 0.05%, the effect of
inhibiting the recrystallized grains from coarsening is less likely
to be obtained, resulting in formation of a nonuniform
metallographic structure in which the recrystallized grains have
partially coarsened. This causes a problem that mottled patterns
are visually confirmed on the surface subjected to surface
treatment such as anodization, or other problem, and results in
poor surface quality. On the other hand, if the Zr content is more
than 0.10%, the Al--Zr-based compounds are distributed more
densely; thus, recrystallization is inhibited to form a fibrous
structure. This causes generation of streak patterns on the
surface-treated surface, and results in poor surface quality.
[0032] Ti:
[0033] Ti is added to seek micronization of crystal grains in the
ingot. The range of Ti content is 0.001% or more and 0.05% or less.
If the Ti content is less than 0.001%, an effect of micronizing the
crystal grains is reduced. Thus, mottled patterns are likely to be
generated on the surface subjected to surface treatment such as
anodization, resulting in poor surface quality. On the other hand,
if the Ti content is more than 0.05%, a point defect is likely to
occur on the surface-treated surface due to Al--Ti-based
intermetallic compounds formed in combination with Al or other
cause, resulting in poor surface quality.
[0034] Other Elements:
[0035] Contained other than the above-listed elements may be
basically Al and inevitable impurities. Elements to be generally
added to the aluminum alloy other than the above-listed elements
are allowed to be present as inevitable impurities, within a range
not greatly affecting the properties of the aluminum alloy.
[0036] In the above-described aluminum alloy material, the mass
ratio of Zn to Mg (Zn/Mg) is 5 or more and 16 or less. As described
above, 7000-series aluminum alloys can generally obtain higher
strength by addition of Zn and Mg. However, addition of a large
amount of Zn reduces hot workability, and addition of a large
amount of Mg facilitates generation of coarse compounds to thereby
reduce surface treatmentability and toughness. Further, general
7000-series alloys are known as having a decreased resistance to
SCC when the metallographic structure thereof is a recrystallized
structure. In the present disclosure, upper limits of the Zn
content and the Mg content are regulated and, further, the mass
ratio (Zn/Mg) is set to be within the above-specified range. As a
result, the following properties can be obtained.
[0037] Specifically, by regulating the upper limits of the Zn
content and the Mg content, the absolute value of the generation
amount of MgZn.sub.2 compounds is made smaller. Further, by setting
the mass ratio (Zn/Mg) to 16 or less, that is, by decreasing the Mg
content relatively and also by regulating the mass ratio (Zn/Mg) to
16 or less, the MgZn.sub.2 compounds are inhibited from growing
coarse. As a result, fine compounds are obtained and toughness can
be improved.
[0038] The resistance to SCC will be discussed below. In general
7000-series aluminum alloys, an electric potential of the matrix in
the vicinity of the grain boundary is nobler than that of the
MgZn.sub.2 compounds precipitated on the grain boundary. Such an
electric potential difference causes a local anodic dissolution
under a stress corrosion environment, thus generating a crack in
the vicinity of the grain boundary. This is considered to cause
stress concentration and, thus, generation and progress of
cracking. In the present disclosure, the mass ratio (Zn/Mg) is set
to 5 or more, that is, an amount of Zn that is solid-solved in the
matrix is made to be relatively large and also the mass ratio
(Zn/Mg) is regulated to 5 or more. This makes it possible to
alleviate the electric potential difference from the MgZn.sub.2
compounds present on the grain boundary, thus improving the
resistance to SCC even in the recrystallized structure.
[0039] As described above, in the present disclosure, a
high-strength aluminum alloy material, which has a good surface
quality and is excellent in toughness and resistance to SCC can be
obtained by regulating the upper limits of the Zn content and the
Mg content and also by setting the mass ratio (Zn/Mg) to 5 or more
and 16 or less.
[0040] In the above-described ranges of the Zn content and the Mg
content, if the mass ratio (Zn/Mg) is less than 5, the effect of
reducing and micronizing the compounds composed of Zn and Mg is
decreased, and the effect of improving toughness cannot be
sufficiently obtained. On the other hand, if the mass ratio (Zn/Mg)
is more than 16, the Zn content becomes larger to thereby cause
anodic dissolution in the vicinity of the grain boundary more
likely, resulting in decrease in resistance to SCC. A preferable
range of the mass ratio (Zn/Mg) is 7 or more and 16 or less.
[0041] The metallographic structure of the above-described aluminum
alloy material comprises an equigranular recrystallized structure.
The recrystallized structure means a metallographic structure
comprising equigranular recrystallized grains. The metallographic
structure can be confirmed by, for example, observing a surface or
a cross-section of the aluminum alloy material with a polarizing
microscope.
[0042] In the above-described aluminum alloy material, it is
preferable that the recrystallized structure be such that: an
average grain diameter of the crystal grains in a cross-section
parallel to a direction orthogonal to a working direction of the
aluminum alloy material (e.g., a direction of extrusion in the case
of an extruded material) is 500 .mu.m or less; and also such that a
difference between the maximum value and the minimum value of the
grain diameters of the crystal grains is less than 300 .mu.m. In
this case, the grain diameters of the crystal grains in the
recrystallized structure are more uniform, and a good surface
quality is thereby obtained. "Working" as in the "working
direction" means extruding, rolling, or other processing. The
"cross-section parallel to a direction orthogonal to a working
direction" means, for example, a cross-section parallel to a width
direction (a cross-section orthogonal to a thickness direction)
when the working direction is assumed to be a length direction.
[0043] If the average grain diameter of the crystal grains in the
recrystallized structure is more than 500 .mu.m, the crystal grains
are excessively coarse, resulting in a risk that mottled patterns
caused by the coarse crystal grains may be generated on the surface
subjected to surface treatment such as anodization. If the
difference between the maximum value and the minimum value of the
grain diameters of the crystal grains is 300 .mu.m or more, the
metallographic structure is nonuniform, resulting in a risk that a
light reflection state may be nonuniform on the surface subjected
to surface treatment.
[0044] The yield strength, as defined in JIS Z2241 (ISO 6892-1), of
the above-described aluminum alloy material is preferably 300 MPa
or more, and more preferably 350 MPa or more. This makes it
possible to relatively easily obtain strength properties applicable
to a lesser wall thickness for weight reduction.
[0045] Next, in a production method for the above-described
aluminum alloy material, an ingot is prepared which comprises the
above-described chemical components and in which the mass ratio of
Zn to Mg (Zn/Mg) is 5 or more and 16 or less, and then a
homogenizing treatment is performed in which the ingot is heated at
a temperature of higher than 540.degree. C. and 580.degree. C. or
lower for 1 hour or longer and 24 hours or shorter.
[0046] If the heating temperature in the above-described
homogenizing treatment is 540.degree. C. or lower, the Al--Zr-based
compounds present in the ingot form a metastable phase having an
L1.sub.2 structure commensurate with the matrix, thus inhibiting
recrystallization in the structure subjected to hot working and
readily leading to formation of a fibrous structure. This causes
generation of streak patterns on the surface subjected to surface
treatment such as anodization, and results in poor surface quality.
Further, a segregated layer in the ingot is not homogenized, and
the structure subjected to hot working becomes a nonuniform
recrystallized structure. As a result, a final surface quality
becomes similarly poor. On the other hand, if the heating
temperature in the above-described homogenizing treatment is higher
than 580.degree. C., the ingot may be melt locally, resulting in
difficulty in practical production.
[0047] Accordingly, the heating temperature in the above-described
homogenizing treatment is set to be higher than 540.degree. C. and
580.degree. C. or lower, whereby the Al--Zr-based compounds present
in the ingot change to an equilibrium phase having a D0.sub.23
structure. This results in formation of an equigranular
recrystallized structure, not a fibrous structure, after hot
working, and also inhibits the recrystallized grains from
coarsening by blocking movement of the crystal grain boundary.
[0048] If the heating time for the above-described homogenizing
treatment is shorter than 1 hour, the segregated layer in the ingot
is not homogenized, and the structure subjected to hot working
becomes a nonuniform recrystallized structure. As a result, a final
surface quality becomes poor similarly to the above. On the other
hand, if the heating time for the above-described homogenizing
treatment exceeds 24 hours, the segregated layer in the ingot is
sufficiently homogenized; thus, no further effect can be expected.
Accordingly, the heating time for the above-described homogenizing
treatment is set to 1 hour or longer and 24 hours or shorter.
[0049] The above-described aluminum alloy material includes, for
example, an extruded material, a plate material, and so on made of
aluminum alloy. The present disclosure can be applied to various
aluminum alloy materials and production methods therefor.
EXAMPLES
Example 1
[0050] Examples of the aluminum alloy material of the present
disclosure will be described through comparison with comparative
examples, with reference to Table 1 and Table 2. The
below-described examples show one embodiment of the present
disclosure, and the present disclosure is not limited to these.
[0051] As shown in Table 1 and Table 2, a plurality of specimens of
the aluminum alloy material (examples: Specimen 1 to Specimen 23,
comparative examples: Specimen 24 to Specimen 38) containing
different chemical components were prepared under the same
production conditions, and various evaluations were conducted on
each specimen. A preparation method and various evaluation methods
for the specimens will be described below.
[0052] <Method for Preparing Specimen>
[0053] A cylindrical ingot (billet) having a diameter of 90 mm
containing chemical components shown in Table 1 is forged by
semicontinuous casting. Then, a homogenizing treatment is performed
in which the ingot is heated at 560.degree. C. for 12 hours. The
heating temperature in the homogenizing treatment may be higher
than 540.degree. C. and 580.degree. C. or lower. Subsequently, the
ingot is subjected to hot extrusion with the temperature of the
ingot maintained at 520.degree. C. In this way, an extruded
material having a width of 150 mm and a thickness of 10 mm is
obtained.
[0054] Next, a quenching treatment is performed in which the
extruded material subjected to hot extrusion is cooled to
100.degree. C. at a cooling rate of 1500.degree. C./min. Then,
after the quenched extruded material is cooled to room temperature,
an artificial aging treatment is performed in which the extruded
material is heated at 140.degree. C. for 12 hours. In this way, a
specimen of the aluminum alloy material (extruded material) is
obtained.
[0055] <Method for Evaluating Mechanical Properties>
[0056] A test piece is prepared from the specimen by a method based
on JIS Z2241 (ISO 6892-1), and a tensile strength, a yield
strength, and an elongation of the test piece are measured. The
test piece having a yield strength of 300 MPa or more is determined
to be acceptable. The criterion for determining the yield strength
is just an example.
[0057] As for a bending test, as shown in FIG. 1, a test piece 10
having a thickness of 10 mm, a width of 10 mm, and a length of 120
mm is prepared from a width-direction central portion of the
specimen, and an amount .DELTA. of bending deformation of the test
piece 10 is measured by a three-point bending test. Specifically, a
jig comprising a base 11 and two supporting portions 12 is
prepared, and the test piece 10 is left at rest on the two
supporting portions 12. At this time, the two supporting portions
12 each support the test piece 10 at a position 10 mm from the
corresponding end of the test piece 10, so that a distance between
supporting points becomes 100 mm. Then, a downward load in a
direction orthogonal to the width direction of the specimen is
applied to the specimen by an indenter 13, the dimension of which
at a leading end surface is 10 mm.times.10 mm. Here, if the amount
.DELTA. of bending deformation after application of the load of
4000 kgf for 10 seconds is more than 4 mm, the test piece 10 is
determined to be unacceptable "X"; if more than 2 mm and 4 mm or
less, the test piece 10 is determined to be acceptable
".largecircle."; and if 2 mm or less, the test piece 10 is
determined to be desirable ".circleincircle.".
[0058] <Method for Evaluating Toughness>
[0059] A Charpy impact test is performed by a method based on JIS
Z2242. Specifically, a test piece having a thickness of 7.5 mm, a
width of 10 mm, and a length of 55 mm is prepared. A longitudinal
direction of the test piece is parallel to a direction of
extrusion, and the test piece has a U-shaped notch having a depth
of 2 mm, formed so as to be orthogonal to the direction of
extrusion. The Charpy impact test is performed on the test piece,
and an impact value is measured. If the impact value is 15
J/cm.sup.2 or more, the test piece is determined to be acceptable,
and if less than 15 J/cm.sup.2, the test piece is determined to be
unacceptable. The criteria for determining the impact value is just
an example.
[0060] <Method for Evaluating Resistance to SCC>
[0061] An SCC test is performed by a method based on JIS Z8711.
Specifically, a test piece having a C-ring shape (outside diameter:
19 mm, inside diameter: 16 mm, thickness: 8 mm) is prepared. Then,
a stress of 90% of the yield strength is applied to the test piece
such that a direction of application of a tensile stress at a
stress-concentrated part corresponds to a direction of extrusion of
the test piece. In such a state and under a temperature environment
of 25.degree. C., the test piece is immersed in salt water with the
concentration of 3.5% for 10 minutes and then dried for 50 minutes.
Such steps as one cycle are repeatedly performed. Thirty days
later, whether a cracking is generated in the test piece is
visually confirmed. If no cracking is generated, the test piece is
determined to be acceptable, and if a cracking is generated, the
test piece is determined to be unacceptable.
[0062] <Method for Observing Metallographic Structure>
[0063] A texture observation of the specimen is performed at a
cross-section parallel to a width direction when the working
direction (the direction of extrusion here) is assumed to be a
length direction. In particular, a portion in the vicinity of a
width-direction center of the cross-section is observed. As shown
in FIG. 2, an extruded material 20 as the specimen is cut, and
three cross-sections in total, that is, a cross-section at a
thickness-direction central position of the extruded material 20
and cross-sections at 1/4 positions from the top and the bottom in
the thickness directions of the extruded material 20, are
electrolytically polished. Then, a microscopic image (e.g., a
photograph shown in a lower part of FIG. 2) of each cross-section
at 50 to 100-fold magnification is obtained using a polarizing
microscope. Subsequently, whether the metallographic structure is
an equigranular recrystallized structure is confirmed from the
obtained microscopic image. If the metallographic structure is
fibrous, the specimen is determined to be acceptable. If the
metallographic structure is nonuniform, the specimen is determined
to be unacceptable. As shown in FIG. 2, a direction of observation
is the thickness direction of the specimen.
[0064] Furthermore, as for the specimen whose metallographic
structure is an equigranular recrystallized structure, the obtained
microscopic image thereof is subjected to image analysis.
Equivalent circle diameters of the crystal grains on the respective
cross-sections are found, and an average grain diameter of the
crystal grains on each cross-section is calculated. In addition,
the greatest diameters and the smallest diameters of the crystal
grains on the respective cross-sections are found, and the greatest
one of the greatest diameters and the smallest one of the smallest
diameters are respectively referred to as a maximum value and a
minimum value. Then, a difference between the maximum value and the
minimum value of the grain diameters of the crystal grains (a grain
diameter difference) is calculated. If the average grain diameter
of the crystal grains on each cross-section is 500 .mu.m or less
and the difference between the maximum value and the minimum value
of the grain diameters of the crystal grains on all the
cross-sections observed (the grain diameter difference) is less
than 300 .mu.m, the specimen is determined to be desirable.
[0065] <Method for Evaluating Surface Quality>
[0066] After a surface of the specimen is mechanically polished
(buffed), the specimen is etched with an aqueous sodium hydroxide
and is further desmutted. Then, the desmutted specimen is
chemically polished by a phosphoric acid-nitric acid method for 1
minute at a temperature of 90.degree. C.
[0067] Next, the chemically polished specimen is anodized at a
current concentration of 150 A/m.sup.2 in a 15% sulfuric acid bath
to form an anodized coating having a thickness of 10 .mu.m. Then,
the anodized specimen is immersed in boiling water to perform a
sealing treatment on the anodized coating. In this way, the
specimen is subjected to a surface treatment (anodization).
[0068] Subsequently, the surface-treated (anodized) surface of the
specimen is visually observed. First, the specimen is observed from
a viewpoint vertical to a surface thereof, and the specimen having
no surface defect, such as a scale-like pattern, a streak pattern,
a mottled pattern, or a point defect, generated on its surface is
determined to be acceptable. Further, the specimen is observed from
a viewpoint at an angle of 30.degree. with respect to its surface,
and the specimen whose light reflection state on its surface is
uniform is determined to be desirable.
[0069] Among the above-described surface defects, the scale-like
pattern is a pattern looking like scales along a grain boundary (a
pattern in which crystal grains are seen more conspicuously)
generated as a result of etching the compounds precipitated on the
grain boundary at pretreatment of the surface treatment, in a case
where the metallographic structure is an equigranular
recrystallized structure. The streak pattern is a pattern looking
like a streak along a grain boundary generated as a result of
etching the compounds precipitated on the grain boundary at
pretreatment of the surface treatment, in a case where the
metallographic structure is a fibrous structure. The mottled
pattern is a pattern generated because differences in the crystal
grain size make the crystal grains partially coarse or fine and
such larger and smaller crystal grains look like mottles after the
surface treatment. The point defect is caused when, for example,
coarse compounds come off by being etched. Concave pits are formed
in a position where the compounds were present, and such concave
pits look like points after the surface treatment.
TABLE-US-00001 TABLE 1 Chemical Composition (mass %) Mass Ratio
Specimen Zn Mg Cu Zr Si Fe Mn Cr Ti Al (Zn/Mg) 1 6.52 1.11 0.01
0.07 0.11 0.08 0.02 0.02 0.03 bal. 5.87 2 8.47 0.98 0.04 0.06 0.08
0.15 0.01 0.03 0.01 bal. 8.64 3 7.05 1.11 0.08 0.07 0.18 0.23 0.03
0.02 0.008 bal. 6.35 4 7.99 1.21 0.01 0.06 0.14 0.21 0.02 0.03 0.03
bal. 6.60 5 7.13 0.52 0.02 0.08 0.23 0.09 0.02 0.03 0.02 bal. 13.71
6 8.11 1.48 0.05 0.07 0.15 0.22 0.02 0.02 0.01 bal. 5.48 7 7.88
1.05 0.02 0.08 0.12 0.20 0.01 0.03 0.03 bal. 7.50 8 8.12 1.29 0.06
0.06 0.13 0.08 0.03 0.03 0.01 bal. 6.29 9 6.94 0.99 0.09 0.07 0.09
0.09 0.02 0.02 0.03 bal. 7.01 10 7.31 1.19 0.03 0.05 0.11 0.18 0.02
0.03 0.008 bal. 6.14 11 7.22 1.35 0.04 0.09 0.17 0.23 0.03 0.03
0.02 bal. 5.35 12 6.99 1.25 0.03 0.08 0.26 0.11 0.02 0.03 0.01 bal.
5.59 13 7.34 0.82 0.07 0.06 0.13 0.25 0.02 0.03 0.009 bal. 8.95 14
6.98 0.94 0.02 0.06 0.22 0.09 0.04 0.02 0.009 bal. 7.43 15 6.81
1.11 0.07 0.08 0.18 0.18 0.03 0.04 0.03 bal. 6.14 16 7.99 1.31 0.07
0.07 0.21 0.20 0.01 0.02 0.001 bal. 6.10 17 8.10 0.98 0.01 0.06
0.16 0.08 0.02 0.01 0.04 bal. 8.27 18 7.29 1.44 0.05 0.08 0.14 0.23
0.03 0.02 0.02 bal. 5.06 19 8.42 0.53 0.08 0.07 0.20 0.15 0.02 0.03
0.01 bal. 15.89 20 7.62 1.07 0.03 0.06 0.12 0.21 0.02 0.02 0.009
bal. 7.12 21 8.21 0.58 0.08 0.07 0.09 0.18 0.01 0.03 0.01 bal.
14.16 22 7.88 1.32 0.05 0.06 0.15 0.09 0.03 0.02 0.03 bal. 5.97 23
7.05 1.15 0.08 0.06 0.11 0.17 0.02 0.01 0.009 bal. 6.13 24 6.45
1.09 0.03 0.08 0.08 0.14 0.03 0.01 0.03 bal. 5.92 25 8.56 1.23 0.06
0.08 0.23 0.18 0.01 0.02 0.008 bal. 6.96 26 6.77 0.47 0.07 0.06
0.09 0.16 0.02 0.01 0.02 bal. 14.40 27 7.87 1.54 0.05 0.07 0.17
0.18 0.01 0.02 0.01 bal. 5.11 28 8.11 1.02 0.11 0.08 0.18 0.13 0.03
0.03 0.03 bal. 7.95 29 7.88 1.11 0.02 0.04 0.21 0.08 0.03 0.02 0.03
bal. 7.10 30 6.89 1.21 0.01 0.12 0.16 0.15 0.03 0.01 0.02 bal. 5.69
31 7.11 1.19 0.04 0.07 0.32 0.21 0.01 0.01 0.01 bal. 5.97 32 7.96
0.88 0.07 0.08 0.22 0.33 0.02 0.03 0.03 bal. 9.05 33 6.96 1.12 0.07
0.06 0.18 0.18 0.05 0.02 0.01 bal. 6.21 34 7.33 0.91 0.05 0.07 0.14
0.14 0.02 0.05 0.009 bal. 8.05 35 8.01 0.92 0.03 0.06 0.20 0.08
0.03 0.03 0.0008 bal. 8.71 36 7.77 1.22 0.05 0.08 0.13 0.21 0.02
0.01 0.07 bal. 6.37 37 6.97 1.41 0.03 0.08 0.08 0.12 0.03 0.02 0.01
bal. 4.94 38 8.44 0.52 0.06 0.07 0.23 0.08 0.02 0.01 0.02 bal.
16.23
TABLE-US-00002 TABLE 2 Resistance Metallographic Structure
Observation Surface Quality Mechanical Properties Toughness to SCC
Average Grain Defect Tensil Yield Elon- Impact Stress Metallo-
grain diameter after Light strength strength gation Bending value
corrosion graphic diameter difference surface reflection Specimen
(MPa) (MPa) (%) test (J/cm.sup.2) cracking structure (.mu.m)
(.mu.m) treatment state 1 344 319 19 .largecircle. 19.2 None
Equigranular 356 269 None Uniform 2 383 355 16 .circleincircle.
17.6 None Equigranular 401 245 None Uniform 3 388 362 16
.circleincircle. 17.1 None Equigranular 365 223 None Uniform 4 403
378 15 .circleincircle. 16.9 None Equigranular 297 262 None Uniform
5 338 311 20 .largecircle. 19.5 None Equigranular 321 278 None
Uniform 6 412 381 14 .circleincircle. 16.9 None Equigranular 332
265 None Uniform 7 396 367 16 .circleincircle. 17.0 None
Equigranular 342 281 None Uniform 8 404 376 15 .circleincircle.
16.8 None Equigranular 358 276 None Uniform 9 371 345 17
.largecircle. 17.9 None Equigranular 367 254 None Uniform 10 379
354 17 .circleincircle. 17.5 None Equigranular 376 243 None Uniform
11 386 359 16 .circleincircle. 17.3 None Equigranular 234 259 None
Uniform 12 391 362 16 .circleincircle. 17.0 None Equigranular 298
228 None Uniform 13 370 339 18 .largecircle. 18.4 None Equigranular
432 252 None Uniform 14 353 324 19 .largecircle. 18.7 None
Equigranular 339 261 None Uniform 15 376 349 16 .largecircle. 18.1
None Equigranular 382 281 None Uniform 16 407 379 15
.circleincircle. 16.7 None Equigranular 412 237 None Uniform 17 377
348 17 .largecircle. 18.0 None Equigranular 399 231 None Uniform 18
397 365 16 .circleincircle. 16.6 None Equigranular 288 256 None
Uniform 19 339 314 21 .largecircle. 22.8 None Equigranular 340 267
None Uniform 20 368 343 17 .largecircle. 17.3 None Equigranular 383
283 None Uniform 21 338 310 22 .largecircle. 24.4 None Equigranular
299 255 None Uniform 22 401 372 15 .circleincircle. 17.1 None
Equigranular 305 271 None Uniform 23 363 336 20 .largecircle. 18.6
None Equigranular 389 312 None Partially nonuniform 24 303 272 24 X
20.9 None Equigranular 410 234 None Uniform 25 -- -- -- -- -- -- --
-- -- -- -- 26 292 264 25 X 22.1 None Equigranular 399 242 None
Uniform 27 402 381 15 .circleincircle. 16.8 None Equigranular 421
269 Scale- Nonuniform like patterns 28 377 352 17 .circleincircle.
17.8 None Equigranular 449 255 Yellowish Uniform 29 401 372 16
.circleincircle. 17.0 None Coarse and -- -- Mottled Nonuniform
nonuniform patterns 30 379 353 17 .circleincircle. 17.9 None
Fibrous -- -- Streak Nonuniform patterns 31 365 339 18
.largecircle. 18.5 None Fibrous -- -- Streak Nonuniform patterns 32
375 348 17 .largecircle. 18.2 None Fibrous -- -- Streak Nonuniform
patterns 33 386 357 16 .circleincircle. 17.7 None Fibrous -- --
Streak Nonuniform patterns 34 371 343 18 .largecircle. 18.1 None
Fibrous -- -- Streak Nonuniform patterns 35 376 345 18
.largecircle. 18.4 None Equigranular -- -- Mottled Nonuniform
patterns 36 379 351 17 .circleincircle. 17.6 None Equigranular 290
267 Point Nonuniform defect 37 365 339 19 .largecircle. 14.1 None
Equigranular 391 246 None Uniform 38 336 311 21 .largecircle. 25.3
Cracking Equigranular 412 268 None Uniform generated
[0070] Evaluation results of the respective specimen are shown in
Table 2. As for the specimens that were not determined to be
acceptable (that were determined to be unacceptable), evaluation
results or the like thereof are indicated with underlines applied
thereto in Table 2.
[0071] As can be seen from Table 2, Specimens 1 to 23, whose
metallographic structures were equigranular recrystallized
structures, were determined to be acceptable or to be acceptable
and also desirable in all evaluation items, that is, in terms of
the mechanical properties (the yield strength and the bending
test), the toughness (the impact value), the resistance to SCC (the
stress corrosion cracking), the metallographic structure
observation (the metallographic structure, the average grain
diameter, and the grain diameter difference), and the surface
quality (the defect after surface treatment, and the light
reflection state). In sum, Specimens 1 to 23 exhibited excellent
properties in terms of the strength, the toughness, and the surface
quality, and also exhibited excellent properties in terms of the
resistance to SCC.
[0072] As for Specimen 23, although no defect after surface
treatment was observed, the light reflection state was partially
nonuniform because the grain diameter difference among the crystal
grains (the difference between the maximum value and the minimum
value) was slightly large. However, such partial nonuniformity was
not bad enough to be a problem in the surface quality. Specimen 23
was determined to be acceptable or to be acceptable and also
desirable in all of the evaluation items other than the light
reflection state. In sum, Specimen 23 exhibited excellent
properties in terms of the strength, the toughness, and the surface
quality, and also exhibited excellent properties in terms of the
resistance to SCC.
[0073] Specimen 24, whose Zn content was too low, was determined to
be unacceptable in terms of the yield strength because the strength
improving effect was not sufficiently obtained. On the other hand,
Specimen 25, whose Zn content was too high, was poor in the hot
workability, resulting in difficulty in performing hot extrusion
with actually used facilities.
[0074] Specimen 26, whose Mg content was too low, was determined to
be unacceptable in terms of the yield strength because the strength
improving effect was not sufficiently obtained. On the other hand,
Specimen 27, whose Mg content was too high, was determined to be
unacceptable due to appearance of the defect after surface
treatment because coarse compounds were present on the grain
boundary to generate scale-like patterns on the anodized
surface.
[0075] Specimen 28, whose Cu content was too high, was determined
to be unacceptable due to appearance of the defect after surface
treatment because its anodized surface was yellowish in color
tone.
[0076] Specimen 29, whose Zr content was too low, was determined to
be unacceptable due to appearance of the defect after surface
treatment because a coarse and nonuniform recrystallized structure
was formed to generate mottled patterns on the anodized surface. On
the other hand, Specimen 30, whose Zr content was too high, was
determined to be unacceptable due to appearance of the defect after
surface treatment because a fibrous structure was formed to
generate streak patterns on the anodized surface.
[0077] Specimen 31, whose Si content was too high, was determined
to be unacceptable due to appearance of the defect after surface
treatment because a fibrous structure was formed to generate streak
patterns on the anodized surface.
[0078] Specimen 32, whose Fe content was too high, was determined
to be unacceptable due to appearance of the defect after surface
treatment because a fibrous structure was formed to generate streak
patterns on the anodized surface.
[0079] Specimen 33, whose Mn content was too high, was determined
to be unacceptable due to appearance of the defect after surface
treatment because a fibrous structure was formed to generate streak
patterns on the anodized surface.
[0080] Specimen 34, whose Cr content was too high, was determined
to be unacceptable due to appearance of the defect after surface
treatment because a fibrous structure was formed to generate streak
patterns on the anodized surface.
[0081] Specimen 35, whose Ti content was too low, was determined to
be unacceptable due to appearance of the defect after surface
treatment because the structure of the ingot was coarse and the
metallographic structure subjected to hot extrusion was nonuniform
to generate mottled patterns on the anodized surface. On the other
hand, Specimen 36, whose Ti content was too high, was determined to
be unacceptable due to appearance of the defect after surface
treatment because coarse intermetallic compounds were generated to
cause a point defect on the anodized surface.
[0082] Specimens 27 and 29 to 36, which were determined to be
unacceptable in terms of the defect after surface treatment, were
nonuniform in the light reflection state.
[0083] Specimen 37, whose mass ratio (Zn/Mg) was too low, was
determined to be unacceptable in terms of the impact value
(toughness) because the impact value was less than 15. On the other
hand, Specimen 38, whose mass ratio (Zn/Mg) was too high, was
determined to be unacceptable in terms of the stress corrosion
cracking (resistance to SCC) because a stress corrosion cracking
was generated in the test of resistance to SCC.
Example 2
[0084] Examples in the production method for the above-described
aluminum alloy material will be described through comparison with
comparative examples, with reference to Table 3 and Table 4. The
below-described examples show one embodiment of the present
disclosure, and the present disclosure is not limited to these.
[0085] In this example, as shown in Table 3, a plurality of
specimens (examples: Specimens A to H, comparative examples:
Specimens I to N) of the aluminum alloy material were prepared
under different production conditions, and various evaluations were
conducted on each specimen. The chemical components of the aluminum
alloy material were similar to those of Specimen 10 or Specimen 11
(see Table 1) of Example 1 described above. A preparation method
for the specimens will be described below. Various evaluation
methods were similar to those in the above-described Example 1.
[0086] <Method for Preparing Specimen>
[0087] A cylindrical ingot (billet) having a diameter of 90 mm
containing chemical components similar to those of Specimen 10 or
Specimen 11 (see Table 1) of the above-described Example 1 is
forged by semicontinuous casting. Then, a homogenizing treatment is
performed in which the ingot is heated at a temperature and for a
period of time shown in Table 3. Subsequently, the ingot is
subjected to hot extrusion with the temperature of the ingot
maintained at 520.degree. C. In this way, an extruded material
having a width of 150 mm and a thickness of 10 mm is obtained.
[0088] Next, a quenching treatment is performed in which the
extruded material subjected to hot extrusion is cooled to
100.degree. C. at a cooling rate of 1500.degree. C./min. Then, the
quenched extruded material is cooled to room temperature, and an
artificial aging treatment is performed in which the extruded
material is heated at a temperature of 140.degree. C. for 12 hours.
In this way, the specimen of the aluminum alloy material (extruded
material) is obtained.
TABLE-US-00003 TABLE 3 Homogenizing treatment Alloy Temperature
Time Specimen (Specimen No.) (.degree. C.) (h) A 10 542 10 B 11 C
10 576 8 D 11 E 10 559 1 F 11 G 10 565 24 H 11 I 10 535 10 J 11 K
10 584 8 L 11 M 10 560 0.5 N 11
TABLE-US-00004 TABLE 4 Resistance Metallographic Structure
Observation Surface Quality Mechanical Properties Toughness to SCC
Average Grain Defect Tensil Yield Elon- Impact Stress Metallo-
grain diameter after Light strength strength gation Bending value
corrosion graphic diameter difference surface reflection Specimen
(MPa) (MPa) (%) test (J/cm.sup.2) cracking structure (.mu.m)
(.mu.m) treatment state A 381 356 17 .circleincircle. 17.5 None
Equigranular 379 244 None Uniform B 389 362 16 .circleincircle.
17.3 None Equigranular 343 261 None Uniform C 379 355 16
.circleincircle. 17.4 None Equigranular 401 233 None Uniform D 385
360 17 .circleincircle. 17.2 None Equigranular 299 259 None Uniform
E 382 356 17 .circleincircle. 17.6 None Equigranular 334 229 None
Uniform F 388 361 17 .circleincircle. 17.1 None Equigranular 420
282 None Uniform G 381 353 16 .circleincircle. 17.3 None
Equigranular 405 245 None Uniform H 387 364 16 .circleincircle.
17.5 None Equigranular 329 229 None Uniform I 380 353 17
.circleincircle. 17.7 None Fibrous -- -- Streak Nonuniform patterns
J 385 358 16 .circleincircle. 17.6 None Fibrous -- -- Streak
Nonuniform patterns K -- -- -- -- -- -- -- -- -- -- -- L -- -- --
-- -- -- -- -- -- -- -- M 379 354 17 .circleincircle. 17.4 None
Coarse and -- -- Mottled Nonuniform nonuniform patterns N 386 359
16 .circleincircle. 17.2 None Coarse and -- -- Mottled Nonuniform
nonuniform patterns
[0089] As can be seen from Table 4, Specimens A to H, whose
metallographic structures were equigranular recrystallized
structures, were determined to be acceptable or to be desirable in
all evaluation items, that is, in terms of the mechanical
properties (the yield strength and the bending test), the toughness
(the impact value), the resistance to SCC (the stress corrosion
cracking), the metallographic structure observation (the
metallographic structure, the average grain diameter, and the grain
diameter difference), and the surface quality (the defect after
surface treatment, and the light reflection state). In sum,
Specimens A to H exhibited excellent properties in terms of the
strength, the toughness, and the surface quality, and also
exhibited excellent properties in terms of the resistance to
SCC.
[0090] In Specimens I and J, which were each homogenized at too low
a temperature, Al--Zr-based compounds having an L1.sub.2 structure
were present and fibrous structures were formed. Thus, Specimens I
and J were determined to be unacceptable due to appearance of the
defect after surface treatment because streak patterns were
generated on the anodized surface.
[0091] In Specimens K and L, which were each homogenized at too
high a temperature, local melting occurred to make it difficult to
perform hot extrusion in the actually used facilities.
[0092] Specimens M and N, which were each homogenized for too short
a time, were determined to be unacceptable due to appearance of the
defect after surface treatment because their metallographic
structures after hot extrusion were nonuniform to generate mottled
patterns on the anodized surface.
[0093] In the above-described Examples 1 and 2, the extruded
materials were evaluated as one embodiment of the aluminum alloy
material of the present disclosure. However, results similar to
those of the above-described Examples 1 and 2 are obtained also in
a case of other embodiments, such as plate materials, for
example.
* * * * *