U.S. patent application number 09/425297 was filed with the patent office on 2002-02-07 for a1-mg-si based aluminum alloy extrusion.
Invention is credited to HIRANO, MASAKAZU, KAWAI, HITOSHI, YOSHIHARA, SHINJI.
Application Number | 20020014287 09/425297 |
Document ID | / |
Family ID | 26397318 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014287 |
Kind Code |
A1 |
YOSHIHARA, SHINJI ; et
al. |
February 7, 2002 |
A1-MG-SI BASED ALUMINUM ALLOY EXTRUSION
Abstract
An Al--Mg--Si based aluminum alloy extrusion having large
strength, absorbable impact energy and resistance against
compressing cracking, wherein the average size of Mg.sub.2Si
precipitation in the [1 0 0] and [0 1 0] directions of the (1 0 0)
plane inside grains is 20 nm or more, the distribution density of
the Mg.sub.2Si precipitation in the [0 0 1] direction of the (1 0
0) plane is 100 or more per .mu.m2, and the size of precipitations
on grain boundaries is 1000 nm or less. Alternatively, in the
Al--Mg--Si based aluminum alloy extrusion, a tensile strength
obtained from a tensile test performed at a strain rate of 1000 per
second is from 150 to 400 N/mm.sup.2 (both inclusive).
Inventors: |
YOSHIHARA, SHINJI;
(SHIMONOSEKI-SHI, JP) ; KAWAI, HITOSHI;
(SHIMONOSEKI-SHI, JP) ; HIRANO, MASAKAZU;
(SHIMONOSEKI-SHI, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT
1755 JEFFERSON DAVIS HWY
FOURTH FLOOR
ARLINGTON
VA
22202
|
Family ID: |
26397318 |
Appl. No.: |
09/425297 |
Filed: |
October 25, 1999 |
Current U.S.
Class: |
148/417 ;
420/534; 420/546 |
Current CPC
Class: |
C22C 21/02 20130101;
C22C 21/08 20130101; C22F 1/05 20130101 |
Class at
Publication: |
148/417 ;
420/534; 420/546 |
International
Class: |
C22C 021/06; C22C
021/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 27, 1998 |
JP |
10-305616 |
Mar 4, 1999 |
JP |
11-056368 |
Claims
What is claimed is:
1. An Al--Mg--Si based aluminum alloy extrusion, wherein the
average size of Mg.sub.2Si precipitation in the [1 0 0] and [0 1 0]
directions of the (1 0 0) plane inside grains is 20 nm or more, the
distribution density of the Mg.sub.2Si precipitation in the [O 0 1]
direction of the (1 0 0) plane is 100 or more per .mu.m.sup.2, and
the size of precipitations on grain boundaries is 1000 nm or
less.
2. The Al--Mg--Si based aluminum alloy extrusion according to claim
1, which comprises an Al--Mg--Si based aluminum alloy comprising
Mg: 0.2-1.6% ("%" represents "% by weight" in all claims) and Si:
0.2-1.8%.
3. The Al--Mg--Si based aluminum alloy extrusion according to claim
2, which comprises an Al--Mg--Si based aluminum alloy comprising
Cu: 1.0% or less.
4. The Al--Mg--Si based aluminum alloy extrusion according to claim
3, which comprises an Al--Mg--Si based aluminum alloy comprising
Mn: 0.05-0.5% or less.
5. The Al--Mg--Si based aluminum alloy extrusion according to claim
4, which comprises an Al--Mg--Si based aluminum alloy comprising
one or more selected from the following: Ti: 0.01-0.1% or less, Cr:
0.01-0.2% and Zr: 0.01-0.2%.
6. The Al--Mg--Si based aluminum alloy extrusion according to claim
1, wherein the texture of the crystal is a fiber texture.
7. The Al--Mg--Si based aluminum alloy extrusion according to claim
1, which has a tensile strength of 200 N/mm.sup.2 or more, and a
proof stress of 150 N/mm.sup.2 or more.
8. An Al--Mg--Si based aluminum alloy extrusion excellent in impact
energy absorption property, wherein a tensile strength obtained
from a tensile test performed at a strain rate of 1000 per second
is from 150 to 400 N/mm.sup.2 (both inclusive).
9. The Al--Mg--Si based aluminum alloy extrusion according to claim
8, which comprises an Al--Mg--Si based aluminum alloy comprising
Mg: 0.2-1.6% and Si: 2-1.8%.
10. The Al--Mg--Si based aluminum alloy extrusion according to
claim 9, which comprises Mg: 0.35-1.1%, Si: 0.5-1.3%, Cu:
0.15-0.7%, Ti: 0.005-0.2% and Zr: 0.01-0.2%, and further comprises
one or two selected from the following: Mn: 0.05-0.5% and Cr:
0.05-0.15%, the balance being Al and impurities.
11. A fabric for a car, which comprises an extrusion of the
Al--Mg--Si based aluminum alloy extrusion according to any one of
claims 1-10.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an aluminum alloy
extrusion, and in particular to an aluminum alloy extrusion which
has the following action: when the extrusion receives compressive
impact load or compressive static load along its extrusive axis
direction, the extrusion absorbs the compressive impact load or
compressive static load. Thus, the aluminum alloy extrusion is
suitably applied in particular to fabrics for cars, for example, a
side member or a bumper stay.
[0002] Recently, attention has been paid to the development of a
fuel-efficient car or an electric car from the viewpoint of the
protection of the environment. For the attainment thereof, it is
essential to make the body of cars light. On the other hand, the
weight of cars tends to increase in order to cope with safety
standards and improve the performance of the cars. Under such a
situation, aluminum alloy extrusions are adopted as, for example, a
bumper reinforcement or a frame of cars, and the demand thereof has
been expanding for car members for the following reasons. The
density of the aluminum alloy extrusions is about one-third of that
of iron. The aluminum alloy extrusions have excellent energy
absorption. Extruding the aluminum alloy allows various kinds of
sectional shapes of extrusions.
[0003] For fabrics for cars, in particular for frames of cars, the
following are required in order to absorb impact energy at the time
of collision: the property that the aluminum alloy extrusions are
deformed into bellows at the time of the collision to absorb the
impact energy effectively; high strength; and resistance against
compressing cracking for generating no cracks at the time of the
deformation into the form of bellows, that is, satisfactory axial
compressing property. As materials of frames of cars, such as a
side member or bumper stay, for which such axial compressing
property is required, for example, Japanese Patent Application
Laid-Open No. 9-256096 discloses an extrusion of Al--Mg--Si based
alloy, which has relatively high corrosion resistance among
high-strength aluminum alloys and is superior in recycling ability
to other aluminum alloys.
[0004] As frames of cars, investigations have mainly been made on
Al--Mg--Si based aluminum alloy extrusions, which have relatively
high strength. Hitherto, however, energy absorption power has
generally been evaluated by cutting an extrusion into a given
length, compressing the cut piece in its axial direction at a
compressive rate of several tens mm/minute to buckle the piece, and
obtain an absorbed energy from the resultant load-displacement
curve, or by observing whether cracks are generated or not with
eyes, as disclosed in, for example, Japanese Patent Application
Laid-Open No. 7-118782. Therefore, even if conventional Al--Mg--Si
based aluminum alloy extrusions exhibit excellent energy absorption
property, it is mere energy absorption property under quasi-static
compressive conditions.
[0005] Incidentally, deformation at the time of actual collision is
generated at a very great deformation speed. Concerning Al--Mg--Si
based alloy extrusions, as well as ordinary materials, extrusions
deformed at a high speed are different from extrusions deformed at
a low speed in strength. For this reason, in the case that even an
extrusion exhibiting satisfactory energy absorption property when
it is statically compressed and deformed is compressed and deformed
at a high speed, compressing cracks are frequently generated so
that its energy absorption property changes.
[0006] Therefore, in order to obtain a material of car frames which
is effective against actual collision, it is necessary to obtain an
aluminum alloy extrusion which exhibits satisfactory energy
absorption property when it is compressed and deformed at a high
speed.
[0007] In the case that the strength of Al--Mg--Si based aluminum
alloy is raised by addition of alloying components or thermal
treatment, the resistance against compressing cracking of the alloy
tends to become poorer as the strength of the alloy becomes higher.
Thus, it has greatly been desired to develop an aluminum alloy
having high strength and satisfactory axial compressing property,
which does not cause compressing cracking.
SUMMARY OF THE INVENTION
[0008] Therefore, an object of the present invention is to provide
an Al--Mg--Si based aluminum alloy extrusion which causes
compressing cracks not to be generated even when deformation in its
axial direction occurs at a high speed, as seen in actual
collision, and which has large absorbable energy and satisfactory
energy absorption property.
[0009] Another object of the present invention is to provide an
Al--Mg--Si based aluminum alloy extrusion suitable for fabrics of
cars excellent in axial compressing property (high strength and
resistance against compressing cracking).
[0010] The inventors made various experiments and researches to
develop an Al--Mg--Si based aluminum alloy extrusion excellent in
axial compressing property. As a result, the inventors have found
that excellent axial compressing property can be obtained if the
followings are within specific ranges: the size and the
distribution of Mg.sub.2Si precipitation in specified directions of
the (1 0 0) plane inside grains of an alloy; and the size of
precipitations such as Mg.sub.2Si on grain boundaries. The present
invention has been made on basis of these findings.
[0011] Thus, a first aspect of the present invention is an
Al--Mg--Si based aluminum alloy extrusion, wherein the average size
of Mg.sub.2Si precipitation in the [1 0 0] and [0 1 0] directions
of the (1 0 0) plane inside grains is 20 nm or more, the
distribution density of the Mg.sub.2Si precipitation in the [0 0 1]
direction of the (1 0 0) plane is 100 or more per .mu.m.sup.2, and
the size of precipitations on grain boundaries is 1000 nm or less.
This Al--Mg--Si based aluminum alloy extrusion has satisfactory
axial compressing property. Therefore, the extrusion is suitable
for use as a crushable member (i.e., a member having such an action
that when it receives compressive impact load or compressive static
load in its axial direction, it crushes in the axial direction to
absorb the impact load or the static load).
[0012] Furthermore, during various experiments and researches for
developing an Al--Mg--Si based aluminum alloy extrusion excellent
in energy absorption property when it is compressed and deformed at
a high speed, the inventors have found that the tensile strength
used in the case of performing a tensile test at a high speed is
closely related to energy absorption property when the extrusion is
compressed and deformed at a high speed.
[0013] Thus, a second aspect of the present invention is an
Al--Mg--Si based aluminum alloy extrusion excellent in impact
energy absorption property, wherein a tensile strength obtained
from a tensile test performed at a strain rate of 1000 per second
is from 150 to 400 N/mm.sup.2 (both inclusive), preferably from 200
to 370 N/mm.sup.2 (both inclusive). The Al--Mg--Si based aluminum
alloy extrusion satisfying these requirements can be deformed in
bellows when it is compressed and deformed at a high speed, to
exhibit excellent impact energy absorption property.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a cross section of an hollow extrusion produced in
Examples.
[0015] FIG. 2 is a view for explaining the method of a compressing
test performed in the Examples.
[0016] FIG. 3 is a view for explaining a high-speed compressing
test performed in the Examples.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0017] In the aluminum alloy extrusion according to the first
aspect of the present invention, reasons for limiting the ranges of
the size and distribution density of the precipitation inside
grains and the size of the grain boundary precipitations.
[0018] [Size of the Precipitation Inside the Grains]
[0019] The Mg.sub.2Si precipitation inside the grains precipitates
in a rod form in the <1 0 0> direction at the time of
artificial aging treatment, so as to disturb dislocation movement.
This causes the strength of the extrusion to be raised. If the
average size of the precipitation in the [1 0 0] and [0 1 0]
directions of the (1 0 0) plane inside the grains is less than 20
nm, the precipitated grains are shorn by the dislocation at the
time of the compression and deformation of the extrusion. In this
case, subsequent dislocation moves very easily on the slip plane
(the (1 1 1)plane), so that straight and coarse slip band texture
is generated. For this reason, stress concentrates on the grain
boundaries so that the grain boundaries are ruptured. Thus, such an
extrusion has poor resistance against compressing cracking. It is
more preferable that the average size of the precipitation is 30 nm
or more. However, if the size of the precipitation is too large,
the strength drops. Thus, it is desirable that the average size
thereof is not over 1000 nm.
[0020] [Distribution Density]
[0021] The distribution density of the Mg.sub.2Si precipitation, as
well as the size of the precipitation, has an influence on the
strength of the extrusion. In the case that the distribution
density of the precipitation in the [0 0 1] direction of the (1 0
0) plane inside the grains is less than 100 per .mu.m.sup.2, the
extrusion has low strength and less absorbed energy at the time of
compression and deformation of the extrusion. Therefore, the
distribution density is set up to 100 per .mu.m.sup.2 or more. In
order to obtain higher strength, the distribution density is
preferably 400 per .mu.m.sup.2 or more. If the distribution density
becomes too large, compressing cracking is liable to occur. Thus,
the distribution density is preferably 2000 per .mu.m.sup.2 or
more.
[0022] The size and the distribution density of the Mg.sub.2Si
precipitation are measured by a measuring method that will be
described later.
[0023] [Grain Boundary Precipitations]
[0024] The Mg.sub.2Si precipitation, a simple substance Si and the
like on the grain boundaries are produced in the cooling after the
extruding or the solution treatment, and have an influence on the
rupture form of the grain boundaries. If the size of the grain
boundary precipitations is over 1000 nm, the precipitations become
starting points of cracks so that the grain boundaries rupture.
This makes the resistance against compressing cracking of the
extrusion poor. The size of the precipitations is preferably 500 nm
or less.
[0025] In the Al--Mg--Si based aluminum alloy extrusion according
to the first aspect of the present invention, its crystal texture
is preferably a fiber texture. The fiber texture is a hot-worked
texture, as seen in extrusions, wherein grains are stretched in its
extrusive direction.
[0026] The strain in a material, when it is deformed, is induced by
the movement of dislocation. This dislocation disappears at a
portion where the arrangement of metal crystal is irregular, such
as a grain boundary. Therefore, lattice gaps accumulate in such a
portion so that strains concentrate on the portion. Thus, the
distribution of the dislocation (that is, the distribution of the
strains) is likely to be more uniform in the material as the size
of its grains is smaller. In order to suppress generation of cracks
at the time of compressing, it is necessary to make
deformation-strains uniform in the material. By suppressing
recrystallization to keep the fiber texture, that is, the grain
boundaries in a fine state, the deformation-strains can be
distributed uniformly in the material to improve strength and
resistance against compressing cracking and enlarge absorbable
energy.
[0027] The Al--Mg--Si based aluminum alloy according to the first
aspect of the present invention is a precipitation hardening alloy
made mainly of Mg and Si. A preferable composition thereof is a
composition comprising Mg: 0.2-1.6%(% represents % by weight
throughout the present specification) and Si: 0.2-1.8%, and
optionally Cu: 1.0% or less, Mn: 0.05-0.5%, and one or more
selected from the following: Ti: 0.01-0.1%, Cr: 0.01-0.2% and Zr:
0.01-0.2%. The balance thereof is Al and impurities. If the amount
of Fe as an impurity is 0.7% or less and each amount and the total
amount of other impurities are 0.05% or less and 0.15%,
respectively, the properties of the present alloy are not aversely
effected.
[0028] Reasons why the amounts of the respective components are
limited are as follows.
[0029] [Mg and Si]
[0030] Mg and Si are elements for forming the Mg.sub.2Si
precipitation and strengthen the alloy. In the case of Mg: less
than 0.2% or Si: less than 0.2%, it is impossible to obtain
strength necessary for a fabric or an energy absorbable member to
which an impact load or static load is applied to its axial
direction. On the other hand, in the case of Mg: over 1.6% or Si:
over 1.8%, the deforming ability of the extrusion drops, so that
secondary working thereof becomes difficult. Moreover, the
deformation in the extrusive axis direction easily causes
compressing cracking. Therefore, the composition of the alloy is
set to comprise Mg: 0.2-1.6% and Si: 0.2-1.8%, and especially
preferable Mg: 0.4-0.8% and Si: 0.7-1.1%.
[0031] [Cu]
[0032] Cu has an action of improving the matrix strength of the
alloy in accordance with the added amount thereof. Thus, Cu may be
appropriately added. In order to obtain this action, the added
amount of is preferably 0.1% or more. However, if the added amount
thereof is over 1%, the alloy has reduced corrosion resistance,
resistance against stress corrosion cracking and weldability.
Furthermore, compressing cracking is liable to occur by the
deformation in the extrusive axial direction. Therefore, if Cu is
added, the upper limit of the amount thereof is 1. 0%. In the case,
the amount thereof is especially preferably from 0.15-0.7%.
[0033] [Mn]
[0034] Mn has effect of suppressing recrystallization of the alloy
texture to make the texture fine. Thus, Mn may be appropriately
added on the basis of this property, Mn has an function for
stabilizing the fiber texture of the extrusion. These effects can
be exhibited by the addition of 0.05% or more of Mn. The addition
of more than 0.5% of Mn causes diffusion of Mg, when the alloy is
thermally heated, to be suppressed so as to deteriorate thermal
treating ability and further causes coarse compounds to be
generated so as to deteriorate resistance against compressing
cracking. For this reason, the added amount of Mn is preferably
from 0.05-0.5%.
[0035] [Ti, Cr and Zr]
[0036] Ti is generated as nuclei at the time of melting and casting
of the alloy, and has an action of making the texture of the cast
product fine. Thus, Ti may be appropriately added. This effect
becomes remarkable by the addition of 0.005% or more of Ti. If the
added amount thereof is over 0.1%, coarse compounds are generated
to cause the deterioration in resistance against compressing
cracking. Thus, the added amount thereof is preferably from 0.01 to
0.1%.
[0037] Cr has a pinning effect in the grain boundaries of the alloy
to stabilize the fiber texture of the extrusion. Thus, Cr may be
appropriately added. This effect can be exhibited by the addition
of 0.01% or more of Cr. However, if the amount thereof is over
0.2%, the initial pressure for extruding working is remarkably
raised. This is not practicable. Thus, the added amount thereof is
preferably from 0.01 to 0.2%.
[0038] Zr also has a pinning effect in the grain boundaries of the
alloy to stabilize the fiber texture of the extrusion. Thus, Zr may
be appropriately added. This effect can be exhibited by the
addition of 0.01% or more of Zr. However, if the amount thereof is
over 0.2%, the effect for stabilizing the fiber texture is not
improved any more. Thus, the added amount thereof is preferably
from 0.01 to 0.2%.
[0039] In order to produce the extrusion of the present invention
by use of the above-mentioned Al--Mg--Si based aluminum alloy, the
alloy is melted and cast in the usual manner to prepare an ingot.
The ingot is then subjected to a homogenizing treatment. The
resultant is hot-extruded into a desired sectional shape, and
immediately thereafter, the extruding is quenched (press-quenched).
Alternatively, the resultant is hot-extruded and then is subjected
to a solution and quenching treatment. The
hot-extruding/press-quenching is a treatment of extruding an ingot
and simultaneously using extruding-temperature to conduct a
solution treatment. It is important that the extruding temperature
is set up to temperature for the solution treatment. In order to
obtain the fiber texture at this time, the extruding-temperature is
set to an appropriate temperature in the manner that the fiber
texture after the extruding is not recrystallized into coarse
recrystallized grains. In the case of the hot-extruding followed by
the solution and quenching treatment, the fiber texture is not
recrystallized into coarse recrystallized grains after the
hot-extruding or during the solution treatment. In order to prevent
the boundary grain precipitation from getting coarse and keep its
size within the above-mentioned range, it is necessary to quench
the alloy immediately after the solution treatment(after the
extruding in the former case). Subsequently, the alloy is subjected
to an aging treatment to precipitate Mg.sub.2Si in the grains.
[0040] The more specifically described producing conditions for
obtaining the extrusion according to the first aspect of the
present invention is as follows:
[0041] homogenizing temperature: 450.degree. C.-550.degree. C.
[0042] homogenizing time: 2 hours-8 hours;
[0043] extruding temperature: 470.degree. C.-530.degree. C.
[0044] aging temperature: 160.degree. C.-230.degree. C.
[0045] aging time: 1 hour-8 hours.
[0046] In the case of using the Al--Mg--Si based aluminum alloy
extrusion according to the first aspect of the present invention
particularly as fabrics for cars such as a side member or a bumper
stay, the extension after the aging treatment preferably has a
tensile strength of 200 N/mm.sup.2 or more and a proof stress of
150 N/mm.sup.2 or more to obtain high absorbable energy.
[0047] According to the first aspect of the present invention, it
is possible to obtain an aluminum alloy extrusion which is very
excellent in axial compressing property and is suitable for fabrics
for cars such as a side member by restricting the size of the
precipitation inside the grains and the distribution density and
the size of the grain boundary precipitations.
[0048] The following will describe the aluminum alloy extrusion
according to the second aspect of the present invention.
[0049] In the second aspect of the present invention, as a tensile
rate at a high-speed tensile test, a strain rate of 1000 per second
is selected. The tensile strength obtained in the tensile test
performed under this condition is decided as an index for
representing energy absorption property at the time of high-speed
compression and deformation of any alloy extrusion. The tensile
test performed under a strain rate of 1000 per second corresponds
to a strain rate of a car material deformed when a car collides at
about 30-40 km/h. The behavior of a car when it collides at 30-40
km/h is similar to that of the car when it collides at any speed
more than 30-40 km/h.
[0050] If the tensile strength at a strain rate of 1000 per second
is less than 150 N/mm.sup.2, the alloy extrusion has only small
absorbable energy at the time of compressing and deforming the
alloy extrusion at a high speed and the alloy extrusion does not
satisfy strength necessary for fabrics for cars. On the other hand,
if the tensile strength at a strain rate of 1000 per second is over
400 N/mm.sup.2, compressing cracking occurs at the time of
compressing and deforming the alloy extrusion at a high speed.
Thus, the alloy extrusion is unsuitable for energy absorbable
members.
[0051] The Al--Mg--Si based aluminum alloy according to the second
aspect of the present invention is a precipitation hardening alloy.
A preferable composition thereof is a composition comprising Mg:
0.2-1.6% and Si: 0.2-1.8%, and optionally (1) Cu: 1.0% or less, (2)
Ti: 0.005-0.2%, and (3) one or more selected from the following:
Mn: 0.05-0.5% or less, Cr: 0.01-0.2% and Zr: 0.01-0.2%. Any one or
a combination of the (1)-(3) may be contained. The balance thereof
is Al and impurities. An especially preferable composition is a
composition comprising Mg: 0.35-1.1%, Si: 0.5-1.3%, Cu: 0.15-0.7%,
Ti: 0.005-0.2%, Zr: 0.01-0.2%, and one or two of Mn: 0.05-0.5% and
Cr: 0.05-0.15%. If the amount of Fe as an impurity is 0.7% or less
and each amount and the total amount of other impurities are 0.05%
or less and 0.15% or less, respectively, the properties of the
present alloy are not aversely effected.
[0052] Reasons why the amounts of the respective components are
limited are essentially the same as in the first aspect of the
present invention.
[0053] In the same way as in the first aspect of the present
invention, it is preferable that the crystal texture is a fiber
texture.
[0054] If the Zr is added in an amount more than the given amount,
resistance against compressing cracking of the alloy extrusion
subjected to over aging treatment is greatly improved. Zr causes a
less drop in press-quenching ability than Mn and Cr. Since Cr
causes deterioration in the surface performance of the extrusion,
it is preferable that Zr is first added and subsequently Mn and/or
Cr are/is added. To exhibit the effect of Zr sufficiently in this
case, the composition of the extrusion is set up to comprise Zr:
0.06-0.2% and further Mn: 0.05-0.5% and Cr: 0.05-0.15%.
[0055] The producing conditions for obtaining the extrusion
according to the second aspect of the present invention is as
follows:
[0056] homogenizing temperature: 450.degree. C.-550.degree. C.
homogenizing time: 2 hours-8 hours;
[0057] extruding temperature: 470.degree. C.-530.degree. C.
[0058] aging temperature: 160.degree. C.-230.degree. C.
[0059] aging time: 1 hour -8 hours.
[0060] According to the second aspect of the present invention, it
is possible to obtain an aluminum alloy extrusion which has
excellent energy absorption property, when being deformed at a high
speed, and is suitable for a raw material of fabrics for cars such
as a side member.
EXAMPLES
[0061] The present invention will be described with comparison of
Examples according to the present invention with Comparative
Examples.
Example 1
[0062] In the usual manner, there were obtained ingots (diameter:
155 mm) of several kinds of aluminum alloys comprising Mg and Si as
mainly-added elements. Next, these ingots were subjected to a
homogenizing treatment at 550.degree. C. for 8 hours. Thereafter,
the respective billets were extruded at an extruding temperature of
500.degree. C. and an extruding speed of 5 m/min. Immediately
thereafter, the resultant extrusions were cooled with water
(average cooling rate: about 12000.degree. C./min.) or air (average
cooling rate: about 190.degree. C./min.) to obtain angular pipes
having a long side of 60 mm, a short side of 40 mm and a thickness
of 2 mm. Their cross section is shown in FIG. 1. Next, these
angular pipes were subjected to an artificial aging treatment to
obtain samples. Tables 1 and 2 show alloy compositions and
treatment conditions of the respective samples.
1TABLE 1 Chemical Components (% by weight) No. Si Fe Cu Mn Mg Cr Zn
Ti Zr 1 0.40 0.15 tr. tr. 0.70 tr. tr. 0.02 tr. 2 0.55 0.15 0.10
0.10 0.70 0.05 tr. 0.02 0.05 3 0.90 0.25 0.50 0.35 0.60 tr. tr.
0.02 0.15 4 0.90 0.25 0.50 0.35 0.60 tr. tr. 0.02 0.15 5 0.90 0.25
0.50 0.35 0.60 tr. tr. 0.02 0.15 6 0.40 0.15 tr. tr. 0.70 tr. tr.
0.02 tr. 7 0.55 0.15 0.10 0.10 0.70 0.05 tr. 0.02 0.05 (tr:
trace)
[0063]
2TABLE 2 Treatment Conditions No. Quenching manner Aging
temperature Aging hour 1 Cooling with water 190.degree. C. 3 hours
2 Cooling with water 190.degree. C. 3 hours 3 Cooling with water
190.degree. C. 3 hours 4 Cooling with water 210.degree. C. 3 hours
5 Cooling with water 160.degree. C. 6 hours 6 Cooling with water
230.degree. C. 3 hours 7 Cooling with air 190.degree. C. 3
hours
[0064] Test pieces according to JIS No. 5 were taken out from these
samples. These test pieces were used to measure their tensile
strength .sigma..sub.B, proof stress .sigma..sub.0.2 and rupture
elongation .delta.according to a metallic material tensile test
defined in JIS Z 2241.
[0065] The respective samples (length: 200 mm) were subjected to
compressing tests. FIG. 2 illustrates a method of the compressing
tests. A load was applied to a sample 1 in its axial direction by
means of a universal test machine 2. Based on the test results, a
displacement-load diagram was prepared. From this diagram,
absorbable energy up to a displacement of 100 mm was obtained.
Cracking resistance was evaluated based on cracks generated in the
compressing test. The samples in which no cracking occurred are
represented by .smallcircle.. The samples in which cracking
occurred are represented by .times..
[0066] Test pieces were taken out from the samples and then a
transmission electron microscope was used to observe the (1 0 0)
plane thereof at 200,000 magnifications. Among respective grains of
Mg.sub.2Si precipitation precipitated in the [1 0 0] and [0 1 0]
directions, only precipitated grains having a length in the [1 0 0]
or [0 1 0] direction of 5 nm or more were measured about their
length. The same (1 0 0) plane was observed to examine the number
of Mg.sub.2Si grains which were precipitated in the [1 0 0]
direction and had a diameter of 1 nm or more. Thus, the
distribution density thereof was obtained. Each of the measurements
was performed concerning 4 visual fields of each of the samples
(total observed area: 0.16 .mu.m.sup.2), and then the average
thereof was obtained. The same samples were used to obtain the
maximum size of precipitations such as Mg.sub.2Si or a simple
substance Si on grain boundaries.
[0067] The thus obtained results are shown in Table 3. These
samples were comprehensively evaluated about aptitude as a raw
material of fabrics for cars, such as a side bumper. The results
are also shown in Table 3. The samples suitable for fabrics for
cars, such as a side bumper, are represented by .smallcircle.. The
samples unsuitable for fabrics for cars, such as a side bumper, are
represented by .times..
3TABLE 3 Test Results Matrix Mg.sub.2Si Distribu- tion Size of
grain Tensile properties density boundary .sigma. .sub.0.2
Compressing properties Average (number per precipitations .sigma.
.sub.B(N/ (N/ Absorbable Cracking Overall Samples size (nm)
.mu.m.sup.2) (nm) mm.sup.2) mm.sup.2) .sigma. (%) energy (J)
resistance evaluation Ex. 1 50.7 150 38.7 208 183 10.1 2350
.smallcircle. .smallcircle. 2 38.0 544 54.6 274 255 11.8 3240
.smallcircle. .smallcircle. 3 33.9 831 39.2 350 316 15.6 4360
.smallcircle. .smallcircle. 4 65.0 594 27.4 310 271 15.2 4170
.smallcircle. .smallcircle. Comp. 1 13.1* 2075 16.8 363 291 19.6
4530 x x 2 85.3 96* 63.5 176 143 10.4 1840 .smallcircle. x 3 26.2
919 1828* 268 244 10.2 2410 x x Ex.: Examples Comp.: Comparative
Examples *: Out of the scope of the first aspect of the present
invention
[0068] As is evident from Table 3, all of samples Nos. 1-4
according to the present invention had axial compressing property
(absorbable energy and cracking resistance). On the other hand, all
of samples Nos. 5-7 according to Comparative Examples had
unsatisfactory axial compressing property.
Example 2
[0069] Aluminum alloy billets having the compositions shown in
Table 4 and having a diameter of 155 mm were first produced by
melting and casting in a usual way.
4TABLE 4 Chemical compositions (% by weight) No. Si Fe Cu Mn Mg Cr
Zn Ti Zr 1 0.90 0.30 0.50 0.35 0.65 tr. tr. 0.02 0.13 2 0.55 0.20
0.10 0.10 0.70 0.05 tr. 0.02 0.05 3 0.40 0.15 tr. tr. 0.60 tr. tr.
0.02 tr. 4 0.40 0.15 tr. tr. 0.60 tr. tr. 0.02 tr. 5 0.59 0.23 0.20
0.15 0.51 tr. tr. 0.02 0.11 6 0.20 0.20 tr. tr. 0.65 tr. tr. 0.02
tr. 7 1.20 0.30 0.90 0.36 1.00 0.15 tr. 0.02 0.13 (tr.: trace)
[0070] Next, these ingots were subjected to a homogenizing
treatment at 550.degree. C. for 4 hours. Thereafter, the respective
billets were extruded at an extruding temperature of 500.degree. C.
and an extruding rate of 5 m/minute, and immediately thereafter the
extrusions were cooled with water (at an average cooling rate of
12000.degree. C./minute) or cooled with air (at an average cooling
rate of 190.degree. C./minute) to produce angular pipes having a
70.times.50 mm section and a thickness of 2 mm. Their cross section
is shown in FIG. 1. These angular pipes were subjected to an
artificial aging treatment to prepare samples. Treating conditions
are shown in Table 5.
5TABLE 5 Treatment conditions No. Quenching manner Aging
temperature Aging hour 1 Cooling with water 190.degree. C. 6 hours
2 Cooling with air 190.degree. C. 3 hours 3 Cooling with air
190.degree. C. 3 hours 4 Cooling with water 190.degree. C. 3 hours
5 Cooling with air 190.degree. C. 3 hours 6 Cooling with water
170.degree. C. 8 hours 7 Cooling with water 190.degree. C. 3
hours
[0071] Test pieces based on JIS No. 5 test pieces disclosed in
Japanese Patent Application Laid-Open No. 10-318894 were taken out
in their longitudinal direction from these samples, and then they
were subjected to a tensile test at a strain rate of 1000 per
second in which the measuring method disclosed in this publication
was used. The results are shown in Table 6.
[0072] The respective samples (length: 200 mm) were subjected to a
compressing test at a high speed. FIG. 3 shows the compressing
test. A load (200 kgf) was applied to the samples in their axial
direction by a dropping weight 3. The load was measured with a load
cell 4. The speed of the dropping weight was about 50 km/hour. On
the basis of the test results, displacement-load diagrams were
prepared. From the displacement-load diagrams, absorbable energies
were measured in the range up to a displacement of 100 mm. Samples
having an absorbable energy of 2000 J or more are represented by
.smallcircle., and samples having an absorbable energy of less than
2000 J are represented by .times.. At the same time, resistance
against compressing cracking of the compressing samples was judged
with naked eyes. Samples in which no cracking occurred are
represented by .smallcircle., and samples in which cracking
occurred are represented by .times.. The results are also shown in
Table 6.
[0073] Furthermore, from these results the samples were evaluated
about aptitude for a raw material of car parts such as a side
bumper. The results are also shown in Table 6. Samples which were
excellent in both of the absorbable energy and resistance against
compressing cracking are represented by .smallcircle., and samples
which were poor in either of them are represented by .times..
6TABLE 6 Test results Tensile strength Absorb- at a strain rate
able of 1000 per energy Cracking No. second (N/mm.sup.2) (J)
resistance Aptitude Example 1 330 3100 .smallcircle. .smallcircle.
2 275 2950 .smallcircle. .smallcircle. 3 205 2450 .smallcircle.
.smallcircle. 4 250 2800 .smallcircle. .smallcircle. 5 266 2930
.smallcircle. .smallcircle. Comparative 6 120 1050 .smallcircle. x
Example 7 440 3500 x x
[0074] Samples Nos. 1-5 satisfying the requirements according to
the second aspect of the present invention were deformed into the
form of bellows, and had good absorbable energy and resistance
against compressing cracking. They were suitable for a material of
car parts such as a side member. Among the samples, sample No. 1
was a sample subjected to an over aging treatment, and had
especially high strength and absorbable energy, i.e., especially
good resistance against compressing cracking. On the other hand,
samples No. 6 and No. 7 were poor in the absorbable energy and the
resistance against compressing cracking, respectively, and thus
were unsuitable for a raw material of car parts.
* * * * *