U.S. patent application number 10/420756 was filed with the patent office on 2003-11-06 for shock absorbing material.
This patent application is currently assigned to KABUSHIKI KAISHA KOBE SEIKO SHO (Kobe Steel, Ltd). Invention is credited to Hirano, Masakazu, Kawai, Hitoshi, Yoshihara, Shinji.
Application Number | 20030207143 10/420756 |
Document ID | / |
Family ID | 26437801 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030207143 |
Kind Code |
A1 |
Kawai, Hitoshi ; et
al. |
November 6, 2003 |
Shock absorbing material
Abstract
A shock absorbing material comprising an Al--Mg--Si series
aluminum alloy having high strength and showing excellent energy
absorbing property when compressed in the axial direction of
extrusion is obtained. The shock absorbing material of the
invention has a hollow cross section, mainly comprises a fibrous
structure and can be manufactured by press quenching just after
extrusion followed by aging. In the press quenching, press
quenching under air-cooling advantageous in view of the dimensional
accuracy or the cost can be adopted. Further, the shock absorbing
material of the invention has excellent cracking resistance to a
compressive load in the lateral direction as well as in the axial
direction. The shock absorbing material of the invention is
suitable as side members or bumper stays in the frame structures of
automobiles.
Inventors: |
Kawai, Hitoshi;
(Shimonoseki-shi, JP) ; Yoshihara, Shinji;
(Shimonoseki-shi, JP) ; Hirano, Masakazu;
(Shimonoseki-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KABUSHIKI KAISHA KOBE SEIKO SHO
(Kobe Steel, Ltd)
3-18, Wakinohama-cho 1-chome, Chuo-ku
Kobe-shi
JP
651-0072
|
Family ID: |
26437801 |
Appl. No.: |
10/420756 |
Filed: |
April 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10420756 |
Apr 23, 2003 |
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10190483 |
Jul 9, 2002 |
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10190483 |
Jul 9, 2002 |
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09540532 |
Mar 31, 2000 |
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Current U.S.
Class: |
428/586 ;
148/440; 420/546; 428/544 |
Current CPC
Class: |
C22C 21/06 20130101;
B21C 23/085 20130101; C22F 1/05 20130101; Y10T 428/12292 20150115;
C22F 1/002 20130101; C22C 21/02 20130101; C22F 1/043 20130101; Y10T
428/12 20150115; C22C 21/08 20130101; C22F 1/047 20130101; B60R
19/03 20130101 |
Class at
Publication: |
428/586 ;
428/544; 420/546; 148/440 |
International
Class: |
C22C 021/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 18, 1999 |
JP |
0011-172319 |
Apr 2, 1999 |
JP |
0011-096622 |
Claims
What is claimed is:
1. A shock absorbing material comprising an Al--Mg--Si series
aluminum alloy containing: from 0.30 to 0.70wt % of Mg; from 0.10
to 0.50wt % of Si in excess of a balanced composition for
Mg.sub.2Si; and from 0.10 to 0.40wt % of one or more of Mn, Cr and
Zr in total, wherein said shock absorbing material is of a hollow
cross section, comprises a microstructure having a fibrous and has
an yield stress of 210 MPa or more.
2. The shock absorbing material as defined in claim 1, wherein said
microstructure further comprises surface recrystallization layer
with the thickness being 10% or less and the thickness of said
fibrous structure is 50% or more for the entire.
3. The shock absorbing material as defined in claim 1, wherein the
total amount of Si is from 0.50 to 0.70wt %.
4. The shock absorbing material as defined in claim 1, further
containing from 0.10 to 0.40% of Cu.
5. The shock absorbing material as defined in claim 1, further
containing from 0.005 to 0.2% of Ti.
6. The shock absorbing material as defined in claim 1, being
obtainable from an aluminum alloy extrusion material and by
conducting press quenching under air cooling just after extrusion
and then conducting aging.
7. The shock absorbing material as defined in claim 1, being
obtainable from an aluminum alloy extrusion material and by
conducting press quenching at a cooling rate of 100 to 300.degree.
C./min just after extrusion and then applying aging.
8. A shock absorbing material comprising an Al--Mg--Si series
aluminum alloy containing: from 0.20 to 1.1wt % of Mg; and from
0.20 to 1.2wt % of Si, wherein said shock absorbing material is of
a hollow cross section and comprises a microstructure having the
thickness of a surface recrystallization layer of 1 to 50% for the
entire thickness with the balance of a fibrous structure, having a
grain size in the direction of the thickness of the surface
recrystallization layer of 200 .mu.m or less, and having an yield
stress of 200 MPa or more.
9. The shock absorbing material as defined in claim 8, containing
from 0.40 to 0.80wt % of Mg and from 0.50 to 1.0wt % of Si.
10. The shock absorbing material as defined in claim 8, further
containing one or more of Mn, Cr and Zr within a range from 0.05 to
0.40% of Mn, from 0.05 to 0.20% of Cr and from 0.05 to 0.20% of
Zr.
11. The shock absorbing material as defined in claim 8, further
containing from 0.05 to 0.7% of Cu.
12. The shock absorbing material as defined in claim 8, further
containing from 0.005 to 0.2% of Ti.
13. A shock absorbing material comprising an Al--Mg--Si series
aluminum alloy containing: from 0.20 to 1.1wt % of Mg; and from
0.20 to 1.2wt % of Si, wherein said absorbing material is of a
hollow cross section and has a thickness reduction ratio of 25% or
more at the ruptured cross section when applying a tensile
test.
14. The shock absorbing material as defined in claim 13, containing
from 0.40 to 0.80wt % of Mg and from 0.50 to 1.1wt % of Si.
15. The shock absorbing material as defined in claim 13, further
containing one or more of Mn, Cr and Zr within a range from 0.05 to
0.40% of Mn, from 0.05 to 0.20% of Cr and from 0.05 to 0.20% of
Zr.
16. The shock absorbing material as defined in claim 13, further
containing from 0.05 to 0.7% of Cu.
17. The shock absorbing material as defined in claim 13, further
containing from 0.005 to 0.2% of Ti.
18. The shock absorbing material as defined in claim 13, being
obtainable by press quenching just after extrusion and then
applying aging treatment.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention concerns a shock absorbing material
comprising an Al--Mg--Si series aluminum alloy extrusion material
and having a function of absorbing impact loads when undergoing
compressive impact loads. The shock absorbing material according to
the present invention is suitable, for example, to side members,
bumper stays or side frames in frame structures of automobiles.
[0003] 2. Related Art
[0004] In the frame structures for automobiles, it has been
considered the use of aluminum alloy hollow extrusion materials in
view of reduction of weight as shock absorbing materials such as
side members or bumper stays. The shock absorbing materials
undergoing axial compressive impact loads are required not to
suffer from Eulerian buckling for the entire shape material
(buckling in which the entire shape material is bent in an angled
form) when undergoing loads in the axial direction of extrusion, to
cause shrinking deformation in a bellows form with no cracks to
provide stable high energy absorption, and have required strength
(yield stress) as frame structural materials for automobiles.
[0005] As aluminum alloy extrusion materials usable as the shock
absorbing material, various Al--Mg--Si series aluminum alloy
extrusion materials which are relatively excellent in corrosion
resistance among high strength aluminum alloys and excellent over
other series aluminum alloys also in view of recycling performance
have been studied so far (for example, Japanese Published
Unexamined Patent Application Hei 6-25783, Japanese Published
Unexamined Patent Application Hei 7-54090, Japanese Published
Unexamined Patent Application Hei 7-118782 and Japanese Published
Unexamined Patent Application Hei 9-256096).
[0006] As described in the publications cited above, when
Al--Mg--Si series aluminum alloy extrusion materials are used for
the shock absorbing materials, press quenching in on-line or
solution/quenching treatment in off-line is generally applied
followed by aging. The aging treatment is applied for improving the
strength of the extrusion materials and stabilizing the
microstructure to prevent progress of spontaneous aging which
deteriorates the cracking resistance during use.
[0007] Press quenching under water-cooling has an advantage capable
of providing substantially equal characteristics with those
obtained by the solution/quenching treatment of applying reheating
after extrusion. However, this results in a difference in the
cooling rate along the cross section due to the difference of the
cross sectional shape or the wall thickness of the extrusion
materials, and makes the temperature distribution not uniform
during cooling to cause distortion. Accordingly, it results in
problems that the accuracy is poor, thickness for the cross
sectional shape is difficult to be reduced and the degree of
freedom for the cross sectional shape is restricted if it is
intended to prevent occurrence of such distortion. There is also an
additional problem that it requires higher cost compared with that
in air-cooling.
[0008] On the other hand, press quenching under air-cooling has a
merit of reduced cost compared with press quenching under
water-cooling. However, since the cooling rate is limited, it
results in a problem that no high strength (particularly, yield
stress) can be obtained depending on the alloy compositions and,
even when a high strength can be obtained, the energy absorption or
the cracking resistance is poor.
[0009] In view of the above, it is an object of the present
invention to provide a shock absorbing material comprising an
Al--Mg--Si series aluminum alloy suitable to press quenching under
air cooling and capable of obtaining high strength.
[0010] Further, Al--Mg--Si series aluminum alloy extrusion
materials involve a worry that spontaneous aging progresses to
deteriorate the cracking resistance when exposed at a high
temperature during use thereof, for example, as side members. Aging
treatment is applied as an essential condition to prevent this in a
case of using heat treated type Al--Mg--Si series aluminum alloy
extrusion materials as a shock absorbing materials. However, when
strength is improved by T5, T6 treatment, it involves a problem of
causing cracks when subjected to axial compressive deformation. If
cracks should occur, shrinking deformation in the bellows-form is
inhibited failing to obtain stable energy absorption.
[0011] Further, it has been demanded recently that Al--Mg--Si
series aluminum alloy extrusion materials can be utilized also as
other frame structural materials for automobiles such as side
frames that undergo lateral impact loads with a view point of
recycling use.
[0012] In view of the above, it is a second object of the present
invention to provide an Al--Mg--Si series aluminum alloy extrusion
material having high strength (yield stress) with excellent
cracking resistance in the axial direction and energy absorbing
property and, at the same time, excellent cracking resistance also
in the lateral direction.
[0013] The present inventors have found an alloy composition and a
structure having high strength (yield stress) and showing excellent
energy characteristics when compressed in the axial direction of
extrusion (showing high energy absorption with no occurrence of
cracks) for the shock absorbing material of an Al--Mg--Si series
aluminum alloy based on the premise of adopting press quenching
under air cooling, which is advantageous in view of the dimensional
accuracy and the cost.
SUMMARY OF THE INVENTION
[0014] The shock absorbing material according to the first
invention comprises an Al--Mg--Si series aluminum alloy which
contains from 0.30 to 0.70wt % of Mg from 0.10 to 0.50wt % of Si in
excess of the balanced composition for Mg.sub.2Si and from 0.10 to
0.40wt % of one or more of Mn, Cr and Zr in total, and has a
fibrous structure, and has an yield. stress of 210 MPa or more,
which is subjected to press quenching under air cooling and then
aging after extrusion into a hollow cross sectional shape.
[0015] The Al--Mg--Si series alloy optionally contains from 0.005
to 0.2% of Ti, from 0.10 to 0.40% of Cu and the like and contains
Fe and other elements as inevitable impurities.
[0016] In the Al--Mg--Si series aluminum alloy extrusion materials,
the addition amount of Mg--Si and transition elements (such as Cu,
Mn, Cr and Zr) is generally increased if it is intended to increase
the strength after the aging treatment, in which precipitates
inevitably increase at the grain boundaries to concentration strain
to the grain boundaries. Further, the quenching sensitivity is
generally increased as the amount of the additive elements
increases and the amount of the precipitates at the boundaries also
increases at a low cooling rate (for example, in air cooled press
quenching which is advantageous in view of the dimensional accuracy
or the cost), tending to cause cracks when crushed under large
impact loads.
[0017] On the contrary, the present inventors have found that
Al--Mg--Si series aluminum alloy extrusion materials tend to cause
cracks if the macrostructure thereof mainly comprises a
recrystallization structure but occurrence of such cracks can be
suppressed even at a high strength if it mainly comprises a fibrous
structure (in a state where the fibrous structure after extrusion
is left as it is with no recrystallization also during a heat
treatment step subsequent to the extrusion step). On the other
hand, it has also been found that the fibrous structure is loosened
when the solution quenching treatment is applied in off-line and
that formation of a surface recrystallization layer to a certain
thickness is advantageous in order to obtain required
characteristics by on-line press quenching.
[0018] The second invention has been accomplished based on the
finding described above.
[0019] The Al--Mg--Si series aluminum alloy shock absorbing
material according to the present invention comprises an Al--Mg--Si
series aluminum alloy of a hollow cross section containing from
0.20 to 1.1wt % of Mg and from 0.20 to 1.2wt % of Si, which is aged
after press quenching having an yield stress of 200 MPa or more and
a surface recrystallization layer with a thickness of 1 to 50% for
the entire part and the crystal grain size in the direction of the
thickness of the surface recrystallization layer is 200 .mu.m or
less.
[0020] The fibrous structure layer is present on the inside of the
surface recrystallization layer of the extrusion material.
[0021] In the course of various experiment and studies for
developing the aluminum alloy extrusion material of excellent
cracking resistance, the present inventors have found that the
reduction rate of thickness along the ruptured cross section of a
JIS No. 5 tensile test piece sampled from an extrusion material of
a hollow cross section is closely related with the cracking
resistance of the extrusion material and have accomplished the
third invention.
[0022] That is, the shock absorbing material of the Al--Mg--Si
series aluminum alloy according to the third invention has a
thickness reduction rate for the ruptured cross section of 25% or
more when applying a tensile test for JIS No. 5 tensile test piece.
The thickness reduction rate for the fractured surface (hereinafter
referred to as draft) is represented by (1-a/a.sub.0).times.100,
assuming the average thickness at the ruptured cross section of the
tensile test piece as a, while assuming the original thickness of
the tensile test piece as a.sub.0.
[0023] The aluminum alloy according to the third invention is an
Al--Mg--Si series aluminum alloy containing from 0.2 to 1.1% of Mg
and from 0.2 to 1.2% of Si.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a view showing a cross sectional shape of an
extrusion material used in examples;
[0025] FIG. 2 is a view for explaining a longitudinal crushing test
for each of the examples (before and after crushing);
[0026] FIG. 3 is a view for explaining a lateral crushing test for
each of the examples (before and after crushing);
[0027] FIG. 4 is a view showing a cross sectional shape of an
extrusion material used in Examples 2 and 3; and
PREFERRED EMBODIMENT OF THE INVENTION
[0028] For obtaining high strength and excellent energy absorbing
characteristic as the shock absorbing material, it is desirable
that the microstructure of the extrusion material is a fibrous
structure (fibrous structure formed by extrusion is left as it is
without recrystallization during the heat treatment step subsequent
to the extrusion step). Generally, the transition elements such as
Mn, Cr and Zr are added to the Al--Mg--Si series aluminum alloy
used for the shock absorbing material but addition of such
transition elements increases the quenching sensitivity of the
alloy. Further, while the strength of the alloy is improved as the
amount of Mg and excessive Si increases, the quenching sensitivity
is also increased.
[0029] In a case of applying water-cooled press quenching or
solution/quenching treatment, quenching is attained with no problem
even when the quenching sensitivity is somewhat sharp and high
strength can be obtained by the subsequent aging treatment.
However, if the quenching sensitivity is increased in the
air-cooled press quenching, high strength can no more be obtained
even by the subsequent aging treatment. That is, if the alloy
element is added with an aim of improving the strength, this may
rather lower the strength.
[0030] In the first invention, the positive function and effect by
the addition of each of the elements is necessary for obtaining
high strength and excellent energy absorbing property by the aging
treatment after air cooled press quenching, but it is essential as
well not to increase the quenching sensitivity. With the view point
described above, an optimal alloy composition is defined for the
impact absorbing material, particularly, undergoing air cooled
press quenching.
[0031] Now, the composition of the extrusion material constituting
the shock absorbing material according to the first invention is to
be explained.
[0032] Mg, Si:
[0033] Mg and Si are bonded to form Mg.sub.2Si and improve the
alloy strength. For obtaining strength required as the frame
structural material of automobiles, Mg has to be added by 0.30% or
more. However, if it is added in excess of 0.70%, the quenching
sensitivity is increased and quenching is not attained by the
air-cooled press quenching failing to attain necessary strength.
Accordingly, the Mg content is defined within a range from 0.30 to
0.70%, preferably, from 0.40 to 0.60% and, more preferably, from
0.45 to 0.55%.
[0034] On the other hand, if the amount of excess Si (Si in excess
of the balanced composition for Mg.sub.2Si, which is defined as
"excess Si amount (%)=total Si amount-0.578.times.Mg amount") is
0.10% or less, required strength can not be obtained. If it exceeds
0.50%, the quench sensitivity is increased and quenching is not
attained by air-cooled press quenching and no required strength can
be obtained. Accordingly, the content of excess Si is defined as
from 0.10 to 0.50%. Within the range for the amount of Mg and the
excess Si, the total Si amount is particularly preferably from 0.5
to 0.7% as a range which can provide high strength and does not
increase the quenching sensitivity not so much. Further, a more
preferred range for the excess amount of Si is from 0.22 to
0.40%.
[0035] Mn, Cr, Zr:
[0036] Mn, Cr, Zr have a function of forming a fibrous structure in
the extrusion material to improve the cracking resistance and one
or more them is added within a range from 0.10 to 0.40% in total.
If the addition amount of the transition elements is less than
0.10%, no fibrous structure is formed or a thick surface
recrystallization layer is formed to cause cracks. If the addition
amount exceeds 0.40%, quenching is not attained by air-cooled press
quenching and required strength as the frame structural materials
for automobiles is not developed. A desired range for each of the
elements is from 0.001 to 0.35% of Mn, from 0.001 to 0.20% of Cr
and from 0.001 to 0.20% of Zr. Further, a more preferred range for
the addition amount of the transition elements in total is from
0.20 to 0.30%. The preferred range for each of the elements is from
0.05 to 0.25% of Mn, from 0.001 to 0.15% of Cr and from 0.05 to
0.18% of Zr. A further preferred range for the addition amount of
the transition elements in total is from 0.22 to 0.28%. The desired
range for each of the elements is from 0.10 to 0.20% of Mn, from
0.001 to 0.10% of Cr and from 0.07 to 0.14% of Zr.
[0037] In the alloy according to the present invention, the
addition amount of the transition elements is defined as the
minimum amount capable of maintaining the fibrous structure in the
extrusion material by air-cooled press quenching. Therefore, when
the solution/quenching treatment is applied in off-line instead of
press quenching, recrystallization proceeds by the heating upon
solution treatment. That is, press quenching is an essential
condition of forming the fibrous structure for the alloy
composition according the present invention.
[0038] Then, the fibrous structure is desirably formed to the
entire cross section of the extrusion material. If the surface
recrystallization layer is formed, it is necessary that the layer
is about at a depth of 500 .mu.m or less (desirably, 300 .mu.m)
from the surface of the extrusion material and the thickness of the
fibrous structure is about 1/2 or more for the entire thickness in
a case of an extrusion material of 1 to 5 mm thickness as in the
frame structural materials for automobiles. This is because
distortion is concentrated at the grain boundaries of the surface
crystallized grains tending to cause cracks since the crystal grain
size is greater compared with the fibrous structure, particularly,
the cooling rate is lower in a case of the water cooled press
quenching compared with that in water cooling and the amount of
precipitates precipitating to the crystal grain boundaries during
cooling step is increased, so that distortion is concentrated to
the grain boundaries of the surface recrystallized grains tending
to cause cracks. If the addition amount for the transition elements
such as Mn is less than the above mentioned range, it is difficult
to keep the thickness for the surface recrystallization layer to
500 .mu.m or less in the air cooled press quenching.
[0039] Cu:
[0040] Cu has a function of improving the strength of the
Al--Mg--Si series aluminum alloy and improving the stress corrosion
cracking resistance, and is added optionally. However, if it is
less than 0.10%, the effect is insufficient. On the other hand, the
extrudability and the general corrosion resistance are deteriorated
if it exceeds 0.40%. Accordingly, the content is preferably from
0.10 to 0.40%. A more preferred range is from 0.15 to 0.35% and a
further preferred range is from 0.18 to 0.30%.
[0041] Ti:
[0042] Ti has a function of refining an ingot structure and is
added properly. However, the refining effect is insufficient if it
is less than 0.005%, whereas it is saturated to form macro
compounds if the addition amount is more than 0.2%. Accordingly,
the Ti content is from 0.005 to 0.2%. A more preferred range is
from 0.01 to 0.10% and a further preferred range is from 0.015 to
0.050%.
[0043] Inevitable Impurity:
[0044] Among inevitable impurities, Fe is an impurity contained by
the greatest amount in the raw aluminum metal and, if present in
excess of 0.35% in the alloy, it would crystallize huge
intermetallic compounds during casting deteriorates mechanical
properties of the alloy. Accordingly, the Fe content is restricted
to 0.35% or less. It is preferably 0.30% or less and, further
preferably, 0.25% or less. Further, upon casting the aluminum
alloy, impurities are intruded in various ways such as from raw
metals and intermediate alloys of the additive elements. There are
various intruding elements but impurities other than Fe scarcely
give effects on the properties of alloy if contained by 0.05% or
less as individual content and 0.15% or less by the total amount.
Accordingly, the content of the impurities is defined as 0.05% or
less as the simple element and 0.15% or less as the total amount.
Among the impurities, B is intruded accompanying addition of Ti by
about 1/5 of the Ti content in the alloy and a more preferred range
is 0.02% or less and a further preferred range is 0.01% or
less.
[0045] In the first invention, the aging treatment is applied after
the air-cooled press quenching for the extrusion material having
the composition described above. The strength (yield stress) after
the aging treatment is defined as 210 MPa or more as the strength
required for the frame structural materials of automobiles. This
strength can be obtained by applying the aging treatment after the
air-cooled press quenching for the extrusion material of the
composition described above. However, out of the range of the
composition, no desired strength can be developed (energy
absorption is lowered as well) or no fibrous structure is formed to
deteriorate the energy absorption characteristics. A preferred
range for the yield stress is 220 MPa or more.
[0046] Desired production conditions in the first invention are to
be described. For obtaining products containing the fibrous
structure in a great amount, a homogenization treatment is applied
at 450.degree. C. to 550.degree. C. for 2 to 8 hours and the
extrusion temperature is defined as 450 to 520.degree. C. The aging
treatment is conducted appropriately at 160 to 230.degree. C. for 1
to 8 hours. An appropriate cooling rate is from 100 to 300.degree.
C./min.
[0047] Then, the composition of the extrusion material according to
the second invention is to be explained.
[0048] Mg, Si:
[0049] Mg and Si are bonded to form Mg.sub.2Si and improve the
alloy strength. For obtaining strength required as the frame
structural material of automobiles, Mg has to be added by 0.20% or
more. However, if it is added in excess of 1.1%, the quenching
sensitivity is increased and quenching is not attained by press
quenching at low cooling rate. As the result, the necessary
strength can not be attained. Accordingly, the Mg content is
defined within a range from 0.20 to 1.1%, preferably, from 0.40 to
0.80% and, more preferably, from 0.40 to 0.60%.
[0050] On the other hand, if the amount of Si is 0.20% or less,
required strength can not be obtained. If it exceeds 1.2%, the
quench sensitivity is increased and quenching is not attained by
press quenching at low cooling rate and no required strength can be
obtained. Accordingly, the content of excess Si is defined as from
0.20 to 1.2%, preferably, from 0.50 to 1.0% and, more preferably,
from 0.50 to 0.70%.
[0051] Mn, Cr, Zr
[0052] The reason for defining the numerical values for the range
of the content is identical with that in the first invention.
However, preferably, one or more of them may be added within a
range from 0.05 to 0.40% for Mn, from 0.05 to 0.20% for Cr and from
0.05 to 0.20% for Zr. More preferably, Mn is from 0.05 to 0.25%, Cr
is from 0.05 to 0.15% and Zr is from 0.05 to 0.15%. Further, the
total amount of addition for the transition elements is from 0.05
to 0.60%, preferably, from 0.10 to 0.40% and, more preferably from
0.2 to 0.3%.
[0053] Cr:
[0054] The reason for defining the numerical values for the range
of the content is identical with that in the first invention.
However, a preferred range is from 0.05 to 0.7% and, more preferred
range from 0.10 to 0.35%.
[0055] Ti:
[0056] The reason for defining numerical values for the range of
the content, and the content are identical with those in the first
invention.
[0057] Surface Recrystallization Layer In the Al--Mg--Si series
aluminum alloy extrusion material described above, it is preferred
that the fibrous structure of the extrusion material is formed
substantially for the entire cross section of the extrusion
material. In a case of the extrusion material of 1 to 5 mm
thickness as in the frame structural materials for automobiles, it
is necessary that the surface recrystallization layer is 50% or
less for the entire thickness. Preferably it is 30% or less. This
is because the recrystallized grains have a larger crystal grain
size compared with the fibrous structure, the amount of
precipitates precipitating to the crystal grain boundaries is
increased in the course of cooling if the cooling rate is low and
distortion is concentrated to the grain boundaries of the surface
recrystallization grains tending to cause crackings.
[0058] On the other hand, the Al--Mg--Si series aluminum alloy
extrusion material having the constitution and the thickness
described above can provide the fibrous structure over
substantially entire cross section of the extrusion material (the
thickness of the surface recrystallization layer is less than 1% of
the entire thickness) at the extrusion rate of 5 m/min or lower.
However, since it takes much time before entering the quenching
zone in the press quenching (on-line) at such a low extrusion rate,
quenching is difficult making it difficult to obtain a required
strength, energy absorption amount and maximum load. Accordingly,
it is necessary that the thickness of the surface recrystallization
layer is 1% or more for the thickness. It is preferably 5% or
more.
[0059] Further, it is preferred that the crystal grain size of the
surface recrystallized grains is 200 .mu.m or less and, further
preferably, 100 .mu.m or less. This is because distortion is
concentrated more tending to cause cracks as the grain size of the
surface recrystallized grains is larger.
[0060] Then, the composition for the extrusion material according
to the third invention is to be explained.
[0061] Mg, Si
[0062] The reason for defining numerical values for the range of
the contents is identical with that in the second invention.
However, a preferred range is from 0.20 to 1.1%, more preferably
from 0.40 to 0.8% of Mg and from 0.20 to 1.2%, more preferably from
0.50 to 1.1% of Si.
[0063] Mn, Cr, Zr
[0064] The reason for defining the numerical values for the range
of the content and the range is identical with that in the second
invention.
[0065] Cu:
[0066] The reason for defining the numerical values for the range
of the content and the range is identical with that in the second
invention.
[0067] Ti:
[0068] The reason for defining the numerical values for the range
of the content and the range is identical with that in the first
invention.
EXAMPLE
[0069] Examples of the present invention are to be explained
below.
Example 1
[0070] Al--Mg--Si series aluminum alloy billets of the chemical
compositions shown in FIG. 1-1 were manufactured by melting by DC
casting, and applied with a soaking treatment at 550.degree. C.
.times.4 hr. Successively, by conducting extrusion under the
conditions of an extrusion temperature at 500.degree. C. and an
extrusion rate of 5 m/min, and press quenching (blower air cooling
(cooling rate: about 190.degree. C./min)) at the position just
after the extrusion to obtain an extrusion material of a hollow
cross section as shown in FIG. 1 (70 mm for longer side, 50 mm for
shorter side and 2 mm for thickness). Then, the extrusion material
was applied with an aging treatment at 190.degree. C. .times.3 hr
to prepare test specimens. The thickness of the recrystallization
layer from the outer surface and the inner surface at the central
portion of the longer side and the shorter side for the cross
section of the test specimen was measured to determine the
thickness as an average value for 8 positions. The result is shown
in Table 1.
1TABLE 1-1 Chemical Composition of Surface Layer (wt %) Thickness
of surface recrystallization No. Si Mg Fe Cu Mn Cr Zr Zn Ti Mn + Cr
+ Zr Excess Si layer (one side) 1 0.58 0.54 0.20 0.20 0.15 tr. 0.09
tr. 0.02 0.24 0.27 200 .mu.m 2 0.66 0.51 0.20 tr. 0.15 tr. 0.13 tr.
0.02 0.28 0.37 100 3 0.61 0.51 0.20 0.20 0.25 tr. 0.13 tr. 0.02
0.38 0.32 50 4 0.60 0.50 0.20 0.35 0.08 0.08 0.10 tr. 0.02 0.26
0.31 50 5 0.30 0.52 0.22 0.19 0.15 tr. 0.10 tr. 0.02 0.25 0.00* 200
6 0.85 0.50 0.23 0.21 0.14 tr. 0.09 tr. 0.02 0.23 0.56* 200 7 0.55
0.25* 0.21 0.20 0.16 tr. 0.09 tr. 0.02 0.25 0.41 200 8 0.56 0.75*
0.18 0.20 0.15 tr. 0.09 tr. 0.02 0.24 0.13 200 9 0.569 0.53 0.19
0.20 tr. tr. 0.09 tr. 0.02 0.09* 0.28 600 10 0.57 0.51 0.21 0.21
0.35 tr. 0.09 tr. 0.02 0.44* 0.28 50 *not satisfying the definition
of the present invention
[0071] JIS No. 5 test specimens were sampled from the test
materials and a tensile test was conducted according to JIS Z 2241.
The result is shown in Table 1-2.
[0072] Further, a static axial crushing test was conducted for the
test materials. The test material of 200 mm length was axially
applied with a static compressive load by an Amsler tester as shown
in FIG. 2, and the test material was compressed by 100 mm, to
obtain a load-displacement curve, and the maximum load and the
absorption energy up to 100 mm were determined. The test result is
also shown together in Table 1-2. The cracking resistance was
evaluated visually in which those free from occurrence of open
cracks was evaluated as ".largecircle." and those with occurrence
of open cracks were evaluated as "X". As the overall evaluation,
those having an yield stress (.sigma..sub.0.2) of 210 MPa or more
and also excellent in cracking resistance were evaluated as
".largecircle." and those poor in one of them were evaluated as
"X"
2TABLE 1-2 Result of Tensile Strength and Compression Test
Compression test Tensile test Maximum load Absorption Cracking
Overall No. .sigma.0.2 (Mpa) .sigma.B (Mpa) Elongation(%) (kN)
energy (J) resistance evaluation 1 228 270 14.1 99.4 3390
.largecircle. .largecircle. 2 232 276 14.0 96.2 3070 .largecircle.
.largecircle. 3 219 261 14.2 89.2 2980 .largecircle. .largecircle.
4 217 252 15.9 88.5 2990 .largecircle. .largecircle. 5 172* 220
17.8 80.3 2610 .largecircle. X 6 116* 187 20.2 67.7 2410
.largecircle. X 7 106* 167 14.5 70.5 2500 .largecircle. X 8 110*
181 19.2 68.1 2530 .largecircle. X 9 240 277 11.6 102 2820 X X 10
136* 197 11.8 72.7 2510 .largecircle. X *not satisfying the
definition of the present invention
[0073] As shown in Table 1-2, alloys (Nos. 1-4) within the range of
the composition defined in the present invention show high yield
stress and excellent energy absorbing characteristics (with no
cracks, high energy absorption) through they were obtained by press
quenching under air cooling.
[0074] On the other hand, alloys (Nos. 5-10) not satisfying the
definition for the composition according to the present invention
can not reach the yield stress of 210 MPa which is a required
strength as the flame structural materials of automobiles, or are
inferior in the cracking resistance and lowered for the energy
absorption although the yield stress is high(No. 9).
Example 2
[0075] Al--Mg--Si series aluminum alloy billets of the chemical
compositions shown in Table 2-1 were manufactured by melting by DC
casting and applied with a soaking treatment at 550.degree. C.
.times.4 hr. Successively, extrusion was conducted at an extruding
temperature of 500.degree. C. and at a extruding rate shown in
Table 1, and air cooled or water cooled press quenching in on-line
was applied just after extrusion to obtain extrusion materials each
of a hollow rectangular cross section as shown in FIG. 4 (having
70-80 mm long or side, 54-60 mm shorter side and 2-5 mm thickness).
Air cooling was applied by a blower air cooling at a cooling rate
of about 190.degree. C./min, whereas water cooling was applied at a
cooling rate of about 10000.degree. C./min. Then, an aging
treatment at 190.degree. C. for 3 hours was applied to the
extrusion materials to obtain test materials.
[0076] For the test materials, thickness of the surface
recrystallization layer (GG layer), crystal grain size in the
surface recrystallization layer, mechanical properties and cracking
resistance in the longitudinal and lateral directions were examined
by the following procedures. The results are shown in Table 2-1 and
Table 2-2.
[0077] Thickness of Surface Recrystallization Layer:
[0078] Along the cross section in parallel with the extruding
direction, 4 points on the surface and 4 points on the rear face
were selected, the thickness of the recrystallization layer was
measured at each of the points, the measured values were averaged
for those on the surface and the rearface respectively, and the
thickness of the GG layer was defined as the sum of the mean values
on the surface and the mean values on the rearface.
[0079] Grain Size,of the Surface Recrystallization Layer:
[0080] Along the cross section parallel with the extruding
direction, four points on the surface and four points on the
rearface were measured by a cutting method from the surface toward
the center of the thickness and the measured values were averaged
as the grain size of the GG layer. The grain size was measured from
the surface toward the center of the thickness in this test,
because the grain size measured along this direction has a
particular concern with the occurrence of cracks (in the present
invention, when the thickness of the surface recrystallization
layer is not sufficiently larger than the grain size of the surface
recrystallization layer and the measurement for the grain size is
difficult, it is defined as: grain size for the surface
recrystallization layer=thickness for the surface recrystallization
layer).
[0081] Mechanical Property;
[0082] JIS No. 5 Test specimens were sampled from the test material
and a tensile test was conducted according to JIS Z 2241.
[0083] Longitudinal Compression Property:
[0084] Using a test material of 200 mm length, a static-compression
load was applied axially as shown in FIG. 2 by an Amsler Tester,
which was compressed to 100 mm thereby obtaining a
load/displacement cure, and the maximum load and the
absorption-energy act 100 mm were determined. The cracking
resistance property was evaluated visually and those free from the
occurrence of cracks were evaluated as ".circleincircle.", those
with occurrence of fine cracks were evaluated as ".largecircle."and
those with occurrence of open cracks were evaluated as "X".
[0085] Lateral Compression Characteristic:
[0086] Using a test material of 200 mm length, a static compressive
load was applied by placing the material horizontally such that the
upper sides were situated on upper and lower positions as shown in
FIG. 3, which was compressed to 20 mm and the cracking resistance
was evaluated visually. Those free from the occurrence of cracks
were evaluated as ".circleincircle.", those with occurrence of fine
cracks were evaluated as ".largecircle." and those with occurrence
of open cracks was evaluated as "X".
3 TABLE 2-1 Extrusion GG layer GG Chemical composition (wt %) rate
Quenching Thickness thickness GG layer layer grain No. Si Fe Cu Mn
Mg Cr Ti Zr (m/min) method (mm) (.mu.m) ratio (%) size (.mu.m)
example 1 0.61 0.22 0.20 0.25 0.51 tr. 0.02 0.13 15 Air 2 200 10 50
cooling 2 0.62 0.23 0.20 0.19 0.51 tr. 0.02 0.14 Air 2 300 30 60
cooling 3 0.64 0.20 0.20 0.15 0.51 tr. 0.02 0.10 Air 2 500 50 12
cooling 4 0.58 0.20 0.20 0.25 0.50 tr. 0.02 0.13 Air 3 300 10 40
cooling 5 0.90 0.20 0.51 0.20 0.60 tr. 0.03 0.10 10 water 2 200 10
80 cooling 6 0.91 0.23 0.50 0.36 0.65 tr. 0.02 0.12 7 water 5 250 5
30 cooling 7 0.92 0.25 0.49 0.19 0.60 tr. 0.02 0.14 water 5 1500 30
90 cooling 8 0.92 0.25 0.49 0.35 0.62 tr. 0.02 0.13 6 water 2 60 3
30 cooling comparative 9 0.86 0.27 0.47 0.32 0.62 0.03 0.02 0.12 3
water 2 0* 0* -- example cooling 10 0.60 0.20 0.20 0.07 0.50 tr.
0.02 0.09 15 Air 2 600 60* 130 cooling 11 0.57 0.17 0.20 tr. 0.49
tr. 0.03 0.09 Air 2 750 75* 80 cooling 12 0.55 0.20 0.10 tr. 0.70
tr. 0.03 tr. Air 2 1000 100* 100 cooling 13 0.55 0.20 0.10 0.09
0.69 0.04 0.02 tr. Air 3 2700 90* 100 cooling 14 0.91 0.23 0.50
0.09 0.61 0.04 0.03 tr. 10 water 2 1800 90* 110 cooling 15 0.89
0.27 0.53 tr. 0.63 tr. 0.02 tr. water 5 5000 100* 110 cooling 16
0.86 0.27 0.47 0.32 0.62 0.03 0.02 0.12 7 Air 2 100 5 20 cooling 17
0.60 0.23 0.20 0.15 0.53 tr. 0.02 0.10 15 Air 2 1000 50 300*
cooling *out of definition of the present invention
[0087]
4 TABLE 2-2 Lateral Result of longitudinal compression test
compression Result of tensile test Absorption Maximum Cracking
Cracking No. .sigma.0.2 (Mpa) .sigma.B (Mpa) Elongation(%) energy
(J) load (kN) resistance resistance example 1 256 207 11.0 2920
75.3 .circleincircle. .circleincircle. 2 256 210 14.1 3200 93.1
.circleincircle. .circleincircle. 3 270 228 12.1 3450 99.4
.largecircle. .largecircle. 4 262 210 12.3 10050 181
.circleincircle. .circleincircle. 5 305 289 13.6 3210 115
.circleincircle. .circleincircle. 6 321 290 13.2 21200 661
.circleincircle. .circleincircle. 7 315 282 14.1 20100 652
.circleincircle. .circleincircle. 8 230 201 14.2 2630 68.9
.circleincircle. .circleincircle. comp. 9 213 155* 16.3 1260 52.6
.circleincircle. .circleincircle. example 10 277 225 12.5 3310 92.2
X X 11 280 228 14.0 3000 102 X X 12 262 230 14.0 2710 99.0 X X 13
270 228 12.5 8250 178 X X 14 295 252 12.7 3010 108 X X 15 341 295
12.8 15200 665 X X 16 202 142* 15.6 1150 48.2 .circleincircle.
.circleincircle. 17 273 231 13.1 2760 97.2 X X *out of definition
of the present invention or inferior to the present invention
[0088] As shown in Table 2-2, those having the GG layer thickness
within the range defined by the present invention (Nos. 1-8) cause
no cracks and show high yield stress and excellent energy absorbing
property (no cracks both in longitudinal and lateral directions,
high absorption energy and maximum load)
[0089] On the other hand, No. 9 not formed with the surface GG
layer has an yield stress of less than 200 MPa, has low absorption
energy and maximum load, those having the GG layer thickness in
excess of the range defined by the present invention (Nos. 10-15)
are poor in the cracking resistance, No. 16 having an yield stress
not reaching 200 MPa although having the GG layer thickness within
the range defined according to the present invention has low
absorption energy and maximum load, and No. 17 with low absorption
energy and having the GG layer crystal grain size in excess of 200
.mu.m is poor in the cracking resistance.
Example 3
[0090] The example of the present invention is to be explained in
comparison with a comparative example out of the definition for the
scope of the claims of the present invention.
[0091] At first, Al--Mg--Si series aluminum alloy billets
(diameter: 155 mm) of the chemical composition shown in the
following Table 3-1 were manufactured by melting by the usual
method and a homogenizing treatment was applied under the condition
of about 540.degree. C..times.4 hours.
[0092] Then, each of the billets was subjected to extrusion under
the conditions at an extrusion temperature of 500.degree. C. and an
extrusion rate of 5 m/min, air cooled or water cooled press
quenching was conducted on-line just after extrusion to manufacture
extrusion materials each of hollow square cross section as shown in
FIG. 4-(1) (a square pipe having an outer shape of 70.times.54 mm
and a thickness of 2 mm). An artificial aging treatment was applied
under the conditions shown in Table 3-1 to prepare test
materials.
5 TABLE 3-1 chemical composition (wt %) Quenching Aging No. Si Fe
Cu Mn Mg Cr Ti Zr method condition 1 0.58 0.18 0.21 0.15 0.54 tr.
0.02 0.09 air cooling 190.degree. C. .times. 3 hr 2 0.61 0.22 0.20
0.25 0.51 tr. 0.03 0.13 air cooling 190.degree. C. .times. 3 hr 3
0.64 0.24 0.20 0.15 0.51 tr. 0.03 0.10 air cooling 190.degree. C.
.times. 3 hr 4 0.66 0.24 0.20 0.15 0.51 tr. 0.03 0.13 air cooling
190.degree. C. .times. 3 hr 5 0.93 0.25 0.51 0.36 0.67 tr. 0.02
0.13 water cooling 210.degree. C. .times. 3 hr 6 0.93 0.25 0.51
0.36 0.67 tr. 0.02 0.13 water cooling 190.degree. C. .times. 3 hr 7
0.93 0.25 0.51 0.36 0.67 tr. 0.02 0.13 water cooling 190.degree. C.
.times. 6 hr 8 0.54 0.20 tr. tr. 0.65 tr. 0.02 tr. air cooling
190.degree. C. .times. 3 hr 9 0.93 0.25 0.51 0.36 0.67 tr. 0.02
0.13 water cooling 160.degree. C. .times. 6 hr
[0093]
6 TABLE 3-2 Lateral thickness Result of longitudinal compression
test compression reduction ratio Result of tensile test Absorption
Maximum Cracking Cracking No. (%) .sigma.0.2 (Mpa) .sigma.B (Mpa)
Elongation(%) energy (J) load (kN) resistance resistance 1 40.0 270
228 14.1 3390 99.4 .largecircle. .largecircle. 2 38.2 256 218 14.2
2800 85.8 .largecircle. .largecircle. 3 35.1 266 236 12.1 3120 98.6
.largecircle. .largecircle. 4 28.3 259 222 12.8 2930 93.6
.largecircle. .largecircle. 5 40.8 314 271 13.2 3530 118
.largecircle. .largecircle. 6 27.6 371 325 13.8 4370 129
.largecircle. .largecircle. 7 35.3 358 310 12.9 4010 125
.largecircle. .largecircle. 8 24.3* 259 230 15.6 2660 99.3 X X 9
23.1* 362 279 20.3 3230 121 X X *out of definition in claims
[0094] JIS No. 5 test specimens were sampled from each of the test
materials, and tensile strength .sigma.B, yield stress
.sigma..sub.0.2, elongation at break (elongation strain) .delta.
were measured in accordance with the tensile test method for the
metal material as defined in JIS Z 2241. The average thickness on
the ruptured surface was measured and the thickness reduction ratio
value defined previously was determined. The result is shown in
Table 3-2.
[0095] Further a longitudinal and lateral crushing test was
conducted for each of the test materials. In the longitudinal
crushing test, a static compression load was applied in the axial
direction by an Amsler Tester as shown in FIG. 2, which was
compressed to 100 mm to obtain a load-displacement curve and a
maximum load and an absorption energy up to 100 mm were determined.
The cracking resistance was evaluated visually and those free from
occurrence of cracks (cracks penetrating the thickness) was
evaluated as ".largecircle."and those with occurrence of open
cracks were evaluated as "X". In the lateral cracking test, the
test material was placed horizontally with the longer sides being
situated at upper and lower positions and static compressive load
was applied to compress the material down to 20 mm and the cracking
resistance was evaluated visually. Evaluation for the cracking
resistance is identical with that of the longitudinal crushing
test. The result was also shown together in Table 3-2.
[0096] As can be seen from Table 3-2, any of Nos. 1 to 7 with the
thickness reduction ratio of 25% or more is excellent both in the
longitudinal and lateral compression cracking resistance. Nos. 8
and 9 with the thickness reduction ratio of less than 25% are poor
in the cracking resistance. In addition, while Nos. 1, 3 have the
yield stress substantially equal with that of No. 8 they show
absorption energy higher by about 20% compared with No. 8. Even in
Nos. 2 and 4 having the yield stress lower than that of No. 8, the
absorption energy is higher than that in No. 8 although the maximum
load is somewhat lower. No. 5 has the yield stress substantially
equal with No. 9 but the absorption energy is higher compared with
No. 9. Nos. 6, 7, which are high in yield stress, show absorption
energy much higher than that of No.9.
[0097] According to the first invention, a shock absorbing material
having high strength (yield stress) and showing excellent energy
absorption property can be obtained by conducting press quenching
under air cooling followed by the by aging treatment for the
Al--Mg--Si series aluminum alloy extrusion material. Further,
according to the present invention, a shock absorbing material
which is advantageous in view of the dimensional accuracy and the
cost compared with that formed by water cooling can be obtained
since this is press quenching under air cooling.
[0098] According to the second invention, a shock absorbing
material having high strength and showing excellent energy
absorption property can be obtained by defining the yield stress,
the ratio of the surface recrystallization layer and the grain size
for the Al--Mg--Si series aluminum alloy extrusion material.
[0099] According to the third invention, since the thickness
reduction ratio is defined to 25% or more, a shock absorbing
material having excellent cracking resistance to the longitudinal
compression and the lateral compression and having high absorption
energy can be obtained.
* * * * *