U.S. patent application number 09/745803 was filed with the patent office on 2001-09-27 for aluminum extruded door beam material.
This patent application is currently assigned to KABUSHIKI KAISHA KOBE SEIKO SHO. Invention is credited to Hirano, Masakazu, Yamashita, Hiroyuki.
Application Number | 20010024734 09/745803 |
Document ID | / |
Family ID | 26489894 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010024734 |
Kind Code |
A1 |
Yamashita, Hiroyuki ; et
al. |
September 27, 2001 |
Aluminum extruded door beam material
Abstract
An aluminum extruded door beam includes an outer flange, an
inner flange, and at least one web for connecting the outer flange
and the inner flange. The outer corners at the extended ends of the
outer flange have a radius R of 2.5 mm or less. The outward corners
at the connections between the web and the inner flange and between
the web and the outer flange have a radius R of 2 mm to 4 mm. The
radius of the outward corners at the connections between the web
and the inner flange and between the web and the outer flange is
1.5 to 2 times the width of the web. The length of the extended
ends of the outer flange is 1 to 2 times the radius R of the
outward corner at the connections between the web and the outer and
inner flanges. The aluminum alloy extruded door beam material
contains 0.8 to 1.5% by weight (hereinafter the same) of Mg and 4
to 7% of Zn, and the recrystallization surface layer has a
thickness of 50 .mu.m or less.
Inventors: |
Yamashita, Hiroyuki;
(Shimonoseki-shi, JP) ; Hirano, Masakazu;
(Shimonoseki-shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
KABUSHIKI KAISHA KOBE SEIKO
SHO
3-18, 1-CHOME, WAKINOHAMA-CHO, CHUO-KU
KOBE
JP
651 0072
|
Family ID: |
26489894 |
Appl. No.: |
09/745803 |
Filed: |
December 26, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09745803 |
Dec 26, 2000 |
|
|
|
09092024 |
Jun 5, 1998 |
|
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Current U.S.
Class: |
428/598 ;
148/439; 148/440; 148/550; 428/595; 428/599 |
Current CPC
Class: |
B60J 5/0444 20130101;
C22C 21/18 20130101; Y10T 428/12375 20150115; Y10T 428/12382
20150115; Y10T 428/12993 20150115; Y10T 428/12354 20150115; Y10T
428/26 20150115 |
Class at
Publication: |
428/598 ;
428/595; 428/599; 148/439; 148/440; 148/550 |
International
Class: |
B21C 023/00; C22F
001/047 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 1997 |
JP |
HEI 9-193225 |
Jun 7, 1997 |
JP |
HEI 9-164995 |
Claims
What is claimed is:
1. An aluminum extruded door beam material comprising an outer
flange, an inner flange, and at least one web for connecting the
outer flange and the inner flange, having at least one
characteristic selected from the group consisting of the following
characteristics (1) to (4); (1) the outer corners at the extended
ends of the outer flange having a radius R of 2.5 mm or less, (2)
the outward corners at the extended connections between the web and
the inner flange and between the web and the outer flange having a
radius R of 2 mm to 4 mm, (3) the radius of the outward corners at
the connections between the web and the inner flange and between
the web and the outer flange being 1.5 to 2 times the width of the
web, and (4) the length of the extended ends of the outer flange
being to 1 to 2 times the radius R of the outward corner at the
connections between the web and the outer and inner flange.
2. An aluminum extruded door beam material according to claim 1,
wherein the aluminum alloy comprises 0.8 to 1.5% by weight
(hereinafter the same) of Mg and 4 to 7% of Zn.
3. An aluminum alloy extruded door beam material according to claim
1, wherein the aluminum alloy comprises 0.8 to 1.5% by weight
(hereinafter the same) of Mg; 4 to 7% of Zn; 0.005 to 0.3% of Ti;
at least one element selected from the group consisting of 0.05 to
0.6% of Cu, 0.2 to 0.7% of Mn, 0.05 to 0.3% of Cr, and 0.05 to
0.25% of Zr: and the balance being Al and incidental
impurities.
4. An aluminum extruded door beam material according to claim 1,
wherein the aluminum alloy comprises 0.8 to 1.5% by weight
(hereinafter the same) of Mg and 4 to 7% of Zn, and the aluminum
alloy has a recrystallization surface layer having a thickness of
50 .mu.m or less.
5. An aluminum extruded door beam material according to claim 4,
wherein a fibrous texture is present below the recrystallization
surface layer.
6. An aluminum extruded door beam material according to claim 5,
wherein the fibrous texture has an aspect ratio of 1:20 or
more.
7. An aluminum extruded door beam material according to claim 1,
wherein the aluminum alloy comprises 0.8 to 1.5% by weight
(hereinafter the same) of Mg; 4 to 7% of Zn; 0.005 to 0.3% of Ti;
at least one element selected from the group consisting of 0.05 to
0.6% of Cu, 0.2 to 0.7% of Mn, 0.05 to 0.3% of Cr, and 0.05 to
0.25% of Zr; and the balance being Al and incidental impurities,
and the aluminum alloy has a recrystallization surface layer having
a thickness of 50 .mu.m or less.
8. An aluminum extruded door beam material according to claim 7,
wherein a fibrous texture is present below the recrystallization
surface layer.
9. An aluminum extruded door beam material according to claim 8,
wherein the fibrous texture has an aspect ratio of 1:20 or
more.
10. An aluminum extruded door beam material according to claim 2,
wherein a fibrous texture is present on the surface of the aluminum
extruded door beam material.
11. An aluminum extruded door beam material according to claim 10,
wherein the fibrous texture has an aspect ratio of 1:20 or
more.
12. An aluminum extruded door beam material according to claim 3,
wherein a fibrous texture is present on the surface of the aluminum
extruded door beam material.
13. An aluminum extruded door beam material according to claim 12,
wherein the fibrous texture has an aspect ratio of 1:20 or
more.
14. An aluminum extruded door beam material according to claim 1,
wherein the inner flange or the outer flange has a cross-section
having extended ends which extend from the connecting section with
the web.
15. An aluminum extruded door beam material comprising 0.8 to 1.5%
by weight (hereinafter the same) of Mg and 4 to 7% of Zn, and the
aluminum alloy has a recrystallization surface layer having a
thickness of 50 .mu.m or less.
16. An aluminum extruded door beam material comprising 0.8 to 1.5%
by weight (hereinafter the same) of Mg; 4 to 7% of Zn; 0.005 to
0.3% of Ti; at least one element selected from the group consisting
of 0.05 to 0.6% of Cu, 0.2 to 0.7% of Mn, 0.05 to 0.3% of Cr, and
0.05 to 0.25% of Zr; and the balance being Al and incidental
impurities, wherein the aluminum alloy has a recrystallization
surface layer having a thickness of 50 .mu.m or less.
17. An aluminum extruded door beam material according to claim 15,
wherein a fibrous texture is present below the recrystallization
surface layer.
18. An aluminum extruded door beam material according to claim 16,
wherein a fibrous texture is present below the recrystallization
surface layer.
19. An aluminum extruded door beam material according to claim 17,
wherein the fibrous texture has an aspect ratio of 1:20 or
more.
20. An aluminum extruded door beam material according to claim 18,
wherein the fibrous texture has an aspect ratio of 1:20 or more.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to aluminum door beams used in
reinforcing members for doors of vehicles, such as automobiles and
trucks. The door beam is arranged in a door to absorb the shock
from a collision in the side direction and to secure safety of
passengers.
[0003] 2. Description of the Related Art
[0004] Recently, the global environment has been regarded as being
of worldwide importance. For example, regulations for reducing gas
emissions including carbon dioxide from automobiles have been
strengthened in many countries in order to suppress global warming.
Accordingly, lightweight automobiles have been in rapid
development.
[0005] A door beam for an automobile is attached to the interior of
a door in order to absorb the shock from a collision. A typical
conventional material used is steel, for example, high-tensile
steel of 150 kgf/mm.sup.2 grade. In recent years, however, the use
of aluminum extrusions has been investigated in view of achievement
of a lightweight automobile.
[0006] Door beams for automobiles (also referred to as impact
beams, impact bars, guard bars, or door side beams) are required to
have high energy absorbability to soften the shock from a
collision. For example, Federal Motor Vehicle Safety Standard
(FMVSS) defines criteria of the bending strength and absorbed
energy to a load applied from the side of a vehicle. At laboratory
tests, these bending properties are evaluated by a three-point
bending strength test simulating side collision of a vehicle as
shown in FIG. 2A, in which a door beam is supported at the two ends
and a load is applied to the center.
[0007] FIG. 2B is a typical schematic load (P) vs. displacement
(.delta.) curve in the three-point bending test shown in FIG. 2A.
FIG. 2B shows that the load reaches a maximum value as the
displacement increases, and then it decreases at a further
displacement because of overload buckling of the aluminum beam. In
general, it is preferred that the maximum load be larger and the
displacement when the buckling occurs be larger, that is, the
energy absorption be larger, as shown by a solid line in FIG. 3.
The energy absorption corresponds to the area represented by
hatched lines in the load (P) vs. displacement (.delta.) curve of
FIG. 2B.
[0008] Stricter properties have been required for door beams being
highly conscious of safety, that is, improvements in maximum load
and energy absorption without an increase in the weight have been
required. For example, in a three-point bending test under a
specified condition for door beams, a current required level of the
maximum load is 1,300 kg, which is considerably higher than the
conventional level 1,100 kg.
[0009] Recently, door beams have been applied to compact cars
having short doors. Since the distance (L) between the two ends in
FIG. 2A is short, in collision of compact cars, a small
displacement (.delta.) causes a larger bending curvature. Thus,
rupture will occur more readily with a small displacement.
SUMMARY OF THE INVENTION
[0010] The present inventors have actively investigated a
technology for achieving an aluminum door beam without an increase
in weight, which has a large maximum load, a large displacement
before buckling (hereinafter referred to as buckling displacement),
a large displacement without rupture, and a large energy absorption
in view of a cross-section and dependence of the surface texture on
the composition of the door beam material.
[0011] The investigation was performed in view of the following two
aspects. First, the rupture of the door beam causes decreased
absorption energy, and the ruptured portion is harmful for the
passenger. Thus, the rupture must be absolutely avoided. A target
of the present invention is to provide a configuration in which
buckling proceeds predominantly before the inner flange at the
extension side breaks by the limit of stress-strain
characteristics.
[0012] Second, another possible method to prevent the rupture of
the door beam is increased thicknesses of the flange and the web;
however, this method caused an increase in weight. Thus, another
target of the present invention is to control the composition and
the surface texture of the door beam material for simultaneously
achieving lightweight and high performance.
[0013] As a result, the present inventors have made the following
finding. In the cross-section of an aluminum door beam, the radius
R of the outer corner at the extended ends of the outer flange
(hereinafter referred to as R.sub.FO) and the radius R of the
outward corner at the connections between the web and the outer and
inner flanges (hereinafter referred to as R.sub.WO) significantly
affect the buckling displacement and energy absorption in the load
(P) vs. displacement (.delta.) curve. In the dependence of the
surface texture on the composition of the door beam material, when
the thickness of the recrystallization layer on the outer surface
of the door beam is reduced or the layer is eliminated, the stress
concentration during bending deformation is prevented and the
energy absorption is improved. This is prominent in a door beam
having a large maximum load.
[0014] The present invention is achieved based on the finding.
[0015] Accordingly, it is an object of the present invention to
provide an aluminum extruded door beam comprising an outer flange,
an inner flange, and at least one web for connecting the outer
flange and the inner flange, the outer corners at the extended ends
of the outer flange having a radius R of 2.5 mm or less.
[0016] It is another object of the present invention to provide an
aluminum extruded door beam material comprising an outer flange, an
inner flange, and at least one web for connecting the outer flange
and the inner flange, the outward corners at the connections
between the web and the inner flange and between the web and the
outer flange having a radius R of 2 mm to 4 mm.
[0017] It is a further object of the present invention to provide
an aluminum extruded door beam material comprising an outer flange,
an inner flange, and at least one web for connecting the outer
flange and the inner flange, the radius of the outward corners at
the connections between the web and the inner flange and between
the web and the outer flange being 1.5 to 2 times the width of the
web.
[0018] It is a still further object of the present invention to
provide an aluminum extruded door beam material comprising an outer
flange, an inner flange, and at least one web for connecting the
outer flange and the inner flange, the length of the extended ends
of the outer flange being 1 to 2 times the radius R of the outward
corner at the connections between the web and the flanges.
[0019] It is still another object of the present invention to
provide an aluminum alloy extruded door beam material comprising
0.8 to 1.5% by weight (hereinafter the same) of Mg; 4 to 7% of Zn;
0.005 to 0.3% of Ti; at least one element selected from the group
consisting of 0.05 to 0.6% of Cu, 0.2 to 0.7% of Mn, 0.05 to 0.3%
of Cr, and 0.05 to 0.25% of Zr; and the balance being Al and
incidental impurities, the thickness of the recrystallization
surface layer being 50 .mu.M or less.
[0020] It is a still further object of the present invention to
provide an aluminum alloy extruded door beam material comprising
0.8 to 1.5% by weight (hereinafter the same) of Mg and 4 to 7% of
Zn, the recrystallization surface layer having a thickness of 50
.mu.m or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a cross-sectional view for illustrating names and
reference symbols for main portions of a door beam in accordance
with the present invention;
[0022] FIG. 2A is a schematic cross-sectional view of a three-point
bending test for a door beam;
[0023] FIG. 2B is a schematic graph of a load (P) vs. displacement
(.delta.) curve in the three-point bending test;
[0024] FIG. 3 is a schematic graph of a load (P) vs. displacement
(.delta.) curve in the three-point bending test;
[0025] FIG. 4 is a cross-sectional view of a typical conventional
aluminum door beam;
[0026] FIG. 5 is a schematic graph for illustrating buckling
displacement of a door beam;
[0027] FIGS. 6A and 6B are cross-sectional views of door beams A
and B, respectively, in a First Embodiment;
[0028] FIG. 7 is a graph including load (P) vs. displacement
(.delta.) curves of the door beams A and B in the three-point
bending test;
[0029] FIGS. 8C, 8D and 8E are cross-sectional views of door beams
C, D and E, respectively, in a Second Embodiment;
[0030] FIG. 9 is a graph including load (P) vs. displacement
(.delta.) curves of the door beams C, D and E in the three-point
bending test; and
[0031] FIG. 10A is a cross-sectional view of door beam F in a Third
Embodiment; and
[0032] FIG. 10B is a cross-sectional view of door beams H and I in
a Fourth Embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] An aluminum extruded door beam in accordance with the
present invention includes an outer flange, an inner flange, and at
least one web for connecting the outer flange and the inner flange.
The outer corners at the extended ends of the outer flange have a
radius R.sub.FO of 2.5 mm or less.
[0034] The corners of extended ends of the flange of a conventional
door beam are rounded as shown in FIG. 4 in view of extrudability,
in contrast, the corners in the present invention are angular.
According to the finding by the present inventors, the angular
corner is resistive to buckling, and thus buckling displacement and
energy absorption are improved. That is, the angular corner of the
extended end of the flange causes a larger width of the extended
end of the flange compared with the rounded corner, hence the
angular corner is resistive to buckling. Further, a load is applied
to a larger area in the angular corner, hence the load is more
dispersed and the angular corner is resistive to buckling. A radius
R.sub.FO larger than 2.5 mm will not cause such an improvement. A
smaller radius R.sub.FO causes further improved buckling
displacement and energy absorption, therefore, it is preferred that
the radius R.sub.FO be 2 mm or less, and more preferably 1 mm or
less. It is preferable that the radius R.sub.FO be 0.5 mm or more
in view of extrudability.
[0035] An aluminum extruded door beam material in accordance with
the present invention includes an outer flange, an inner flange,
and at least one web for connecting the outer flange and the inner
flange, and the outward corners at the connections between the web
and the inner flange and between the web and the outer flange have
a radius R.sub.WO of 2 mm to 4 mm.
[0036] In conventional door beams, the R.sub.WO is determined in
view of extrudability. The present inventors discovered that the
radius R.sub.WO significantly affects the buckling displacement and
that the buckling displacement is significantly improved when the
radius R.sub.WO ranges from 2 mm to 4 mm. The buckling at the
extended ends of the outer flange is not substantially prevented
when the radius R.sub.WO is less than 2 mm, and thus the buckling
displacement and energy absorption of the door beam are not
improved. Even when the radius R.sub.WO is larger than 4 mm, the
buckling is not further improved and the weight is unintentionally
increased.
[0037] Thus, it is presumed that when the radius R.sub.WO is larger
than the desired size the extended end of the flange is protected
from the load applied to the extended end. When the radius R.sub.WO
has an unnecessary large size, the weight is increased whereas the
protective effects of the flange does not further increase.
[0038] In another embodiment, an aluminum extruded door beam
material includes an outer flange, an inner flange, and at least
one web for connecting the outer flange and the inner flange, and
the radius R.sub.WO of the outward corners at the connections
between the web and the inner flange and between the web and the
outer flange is 1.5 to 2 times the width t.sub.W of the web.
[0039] When the radius R.sub.WO is 1.5 to two times the width
t.sub.W of the web, the buckling displacement and energy absorption
are more effectively improved. A radius R.sub.WO of less than 1.5
times the width t.sub.W does not cause such an improvement, whereas
a radius R.sub.WO of larger than 2 times does not cause a further
improvement in prevention of buckling but causes an undesired
increase in the weight.
[0040] In still another embodiment in accordance with the present
invention, an aluminum extruded door beam material includes an
outer flange, an inner flange, and at least one web for connecting
the outer flange and the inner flange, and the length L.sub.F of
the extended ends of the outer flange is 1 to 2 times the radius
R.sub.WO of the outward corner at the connections between the web
and the flanges.
[0041] A cross-section satisfying both the length L.sub.F and the
radius R.sub.WO contributes to significant improvement in buckling
displacement and energy absorption. When the length L.sub.F is
smaller than the radius R.sub.WO, the buckling displacement is not
substantially improved, whereas a length L.sub.F which is 2 times
or more the radius R.sub.WO does not cause further improvement in
the buckling displacement, considering undesirable increase in the
weight.
[0042] In still another embodiment in accordance with the present
invention, an aluminum alloy extruded door beam material comprises
0.8 to 1.5% by weight (hereinafter the same) of Mg and 4 to 7% of
Zn, and the recrystallization surface layer has a thickness of 50
.mu.m or less.
[0043] It is preferable to control the texture of the door beam
material so that a fibrous texture is present below the
recrystallization layer. The recrystallization layer may be not
present. In such a case, the fibrous texture is present on the
surface of the material.
[0044] Preferably, the fibrous texture has an aspect ratio of 1:20
or more. A thick recrystallization layer on the surface causes a
rough surface in the bending deformation process, and the rough
surface functions as a notch causing stress concentration. Thus,
the door beam will be rapidly ruptured.
[0045] Preferably, a door beam has two or more among the
above-mentioned features.
[0046] In the present invention, the term "aluminum" means both
"aluminum" and "aluminum alloys".
[0047] The preferred embodiments of the present invention will now
be described with reference to the attached drawings.
[0048] FIG. 1 is a cross-sectional view of a door beam in
accordance with the present invention. The door beam includes an
inner flange F.sub.I, an outer flange F.sub.O, and webs W with a
width t.sub.W, which connect the inner flange F.sub.I, and the
outer flange F.sub.O. The inner flange F.sub.I is arranged toward
the inner side of a vehicle when the door beam is assembled onto a
door, and the outer flange F.sub.O is arranged toward the outer
side of the vehicle. The outer flange F.sub.O has extended ends
with a length L.sub.F, and the outer corners of the extended ends
have a curvature radius of R.sub.FO. The outward corners of the
connections between the outer flange and the webs have a curvature
radius of R.sub.WO.
[0049] The shape of the door beam in accordance with the present
invention is not limited to that shown in FIG. 1. For example, a
door beam having only one web, that is, an I-shaped door beam is
included in the scope of the present invention.
[0050] The buckling displacement in the present invention is
defined as a displacement (.delta.) when the load becomes half the
maximum load (P) in the deformation region after the maximum load
is applied, as shown in FIG. 5.
[0051] [First Embodiment]
[0052] Aluminum door beams A and B having the cross-sectional sizes
shown in FIGS. 6A and 6B, respectively, were formed by extrusion of
an Al--Mg--Zn alloy composed of 1.4% by weight (hereinafter the
same) of Mg, 6.5% of Zn, 0.2% of Cu, 0.15% of Zr, 0.02% of Ti, and
0.3% of Cr, as follows. The alloy was melted by a conventional
process and cast to form an ingot with a diameter of 200 mm. The
ingot was subjected to homogenizing heat treatment at 470.degree.
C. for 8 hours and then extrusion at a temperature of 470.degree.
C. and an extrusion rate of 4 m/min to form the door beams A and B.
The extruded door beams A and B were subjected to artificial aging
at 130.degree. C. for 12 hours. The outer flange of the door beam A
has a length of 38 mm and a width of 4.4 mm, the inner flange has a
length of 48 mm and a width of 4.6 mm, and the web has a length of
28 mm and a width of 2.1 mm. In the door beam A, the length L.sub.F
of the extended ends of the outer flange O.sub.F and the curvature
radius R.sub.FO of the outer corners of the extended ends are
different from those of door beam B, and other portions have the
same size.
[0053] A cut piece was prepared from each of the door beams A and
B, and subjected to the three-point bending test shown in FIG. 2A
at a bending span L of 1,200 mm. A load was applied before the
displacement (.delta.) reached 350 mm. FIG. 7 is a load (P) vs.
displacement (.delta.) curve in the three-point bending test. Table
1 shows the maximum load, buckling displacement, energy absorption,
and the unit weight of the door beam.
1TABLE 1 Maximum Buckling Energy Unit R.sub.FO load displacement
absorption weight Door Beam (mm) (kgf/mm.sup.2) (mm) (kgf
.multidot. mm) (kg/m) Judgement A (For 3.0 1,289 214 247,805 1.40
No comparison) (1.00) (1.00) (1.00) (1.00) good B 0.5 1,278 250
272,634 1.38 Good (Example) (0.99) (1.17) (1.10) (0.99) Remarks:
values in parentheses represent the relative values to those of the
door beam A (1.00). R.sub.FO represents the curvature radius R of
the outer corners at the extended ends of the outer flange.
[0054] As shown in Table 1, the door beam B having an R.sub.FO in
accordance with the present invention shows a similar maximum load,
a buckling displacement higher by 17%, and an energy absorption
higher by 10% regardless of a slightly smaller unit weight compared
to those of the door beam A for comparison having an R.sub.FO out
of the scope of the present invention. Such advantages can also be
achieved with JIS 7N01, 6061, 6063 and 6N01 alloys, and Alloys 6000
and 7000 series in a list published by Aluminum Association, such
as Alloy 6082. 7000 series alloys containing 0.8% to 1.5% of Mg and
4% to 7% of Zn, by weight respectively, are preferred in view of
strength and extrudability, as described below in detail.
[0055] [Second Embodiment]
[0056] Aluminum door beams C, D and E having the cross-sections
shown in FIGS. 8C, 8D and 8E, respectively, were formed using the
Al--Mg--Zn alloy having the same composition as the First
Embodiment. The details of the cross-sections of these door beams
C, D and E are shown in Table 2. The lengths and the thicknesses of
the outer flange and the inner flange, the length of the webs, and
the distance between the webs are the same in the door beams C, D
and E.
2TABLE 2 Door beam R.sub.WO (mm) R.sub.WO/t.sub.W L.sub.F/R.sub.WO
R.sub.FO (mm) C (For 1 0.53 6.85 3 comparison) D (Example) 4* 2.11
1.71* 1.8* E (Example) 4* 1.82* 1.64* 1.8* Remarks: Asterisk*
indicates that it is within the scope of the present invention.
R.sub.WO: Curvature radius of the outward corners of the
connections between the outer flange and the webs t.sub.W: Web
width L.sub.F: Length of the extended ends of the outer flange
R.sub.FO: Curvature radius of the outer corners of the outer
flange
[0057] A cut piece was prepared from each of the door beams C, D
and E, and subjected to the three-point bending test shown in FIG.
2A at a bending span L of 950 mm. A load was applied before the
displacement (.delta.) reached 300 mm. FIG. 9 is a load (P) vs.
displacement (.delta.) curve in the three-point bending test. Table
3 shows the ratios of the energy absorption and the unit weight of
the door beam.
3TABLE 3 Ratio of absorption Door Beam Weight ratio energy C (For
comparison) 1.00 1.00 D (Example) 1.05 1.29 E (Example) 1.09
1.73
[0058] As shown in Table 3, the door beam D in accordance with the
present invention, which satisfies the R.sub.WO, LF/R.sub.WO and
R.sub.FO ratios, shows an increase by 29% in energy absorption to
the door beam C for comparison, regardless of a slight increase by
5% in weight to the door beam C. The door beam E in accordance with
the present invention, which also satisfies the R.sub.WO/t.sub.W
ratio, as well as the R.sub.WO, LF/R.sub.WO and R.sub.FO ratios,
shows a significant increase by 73% in energy absorption to the
door beam C for comparison, regardless of a slight increase by 9%
in weight to the door beam C.
[0059] In the configurations in Second Embodiment, such advantages
can also be achieved with JIS 7N01, 6061, 6063 and 6N01 alloys, and
Alloys 6000 and 7000 series registered in a list published by
Aluminum Association, such as Alloy 6082. Open-type 7000 series
alloys containing 0.8% to 1.5% by weight of Mg and 4% to 7% by
weight of Zn are preferred in view of strength and extrudability,
as described below in detail.
[0060] As described above, there are the following four design
requirements for aluminum door beams:
[0061] (A) An R.sub.FO of 2.5 mm or less.
[0062] (B) An R.sub.WO ranging from 2 mm to 4 mm.
[0063] (C) An R.sub.WO/t.sub.W ratio ranging from 1.5 to 2.
[0064] (D) An L.sub.F/R.sub.WO ratio ranging from 1 to 2.
[0065] Any combination of these requirements causes further
improvement in the buckling displacement and energy absorption.
Preferred combinations of the requirements include (A) and (B); (A)
and (C); (A) and (D); (B) and (C); (B) and (D); (C) and (D); (A),
(B) and (C); (A), (B) and (D); (A), (C) and (D); (B), (C) and (D);
and (A), (B), (C) and (D).
[0066] The curvature R.sub.FI of the inner corners at the extended
ends of the outer flange F.sub.O affects the mechanical properties
compared less than that of the R.sub.FO of the outer corner, and it
is not necessary that both are equal to each other; however, it is
preferable that the R.sub.FI be 2.5 mm or less, more preferably 2
mm or less, and most preferably 1 mm or less, as in the
R.sub.FO.
[0067] The curvature of the corners at the extended ends of the
inner flange F.sub.I can be determined without restriction based on
the practical design of the door beam. For example, when the
extended ends of the inner flange F.sub.I are used for attaching
the door beam to the vehicle door and a flat surface is required,
it is preferable that the corner has a smaller curvature. On the
contrary, it is preferable that the curvature be larger in view of
extrudability and surface characteristics.
[0068] Although the curvature of the inward corners (at the hollow
section in FIG. 1) of the connections between the webs and the
inner and outer flanges is not limited, it is preferable that the
curvature ranges from 2 mm to 4 mm and that it be 1.5 to 2 times
the web width.
[0069] An inner flange F.sub.I longer than the outer flange F.sub.O
or an extended end of the inner flange F.sub.I longer than the
extended end of the outer flange F.sub.O causes a shift of the
neutral axis towards the inner side (passenger side) of the
vehicle. Such a shift causes increased energy absorption and
delayed rupture of the door beam at the inner side by a collision
load.
[0070] In the present invention, the door beam comprises an outer
flange which lies in the outer side of the vehicle and is loaded
with an impact load in the vertical direction, an inner flange
which lies substantially parallel to the outer flange and lies in
the passenger side, and at least one web connecting these flanges,
and the inner flange or the outer flange preferably has a
cross-section having extended ends which extend from the connecting
section with the web.
[0071] In the present invention, another flange may be provided
between the inner flange and the outer flange.
[0072] [Third Embodiment]
[0073] An aluminum alloy of Composition 1 shown in Table 4 was
melted by a conventional process and cast to form an ingot with a
diameter of 200 mm. The ingot was subjected to homogenizing heat
treatment at 470.degree. C. for 8 hours and then extrusion at a
temperature of 470.degree. C., an extrusion rate of 4 m/min and an
extrusion ratio of 42 to form two door beams F having a
cross-section shown in FIG. 10A. The extruded door beams F were
immediately cooled by blowing liquid nitrogen and cooled nitrogen
gas and subjected to artificial aging at 130.degree. C. for 12
hours.
[0074] The same aluminum alloy ingot was subjected to homogenizing
heat treatment at 470.degree. C. for 8 hours and then extrusion at
a temperature of 500.degree. C., an extrusion rate of 12 m/min and
an extrusion ratio of 83 to form a door beam G having the same
cross-section shown in FIG. 10A. The extruded door beam G was
subjected to artificial aging at 130.degree. C. for 12 hours
without cooling by liquid nitrogen and cooled nitrogen gas.
4 TABLE 4 Chemical component (wt %) Compound Mg Zn Ti Cu Mn Cr Zn 1
1.3 6.7 0.03 0.2 0.2 0.06 0.14 2 0.72 5.5 0.04 0.07 0.02 0.02
0.18
[0075] Table 5 shows the results of the thickness of the
recrystallization surface layer, the aspect ratio of the fibrous
texture, and the three-point bending test at a bending distance of
950 mm of the door beams F and G. As shown in Table 5, the door
beams F, which were within the scope of the present invention in
terms of the thickness of the recrystallization surface layer and
the aspect ratio of the fibrous texture, had a larger rupture
displacement compared with that of the door beam G having a larger
thickness and a lower aspect ratio.
5TABLE 5 Thickness of Aspect recrystal- ratio Maximum Rupture
lization of bending displace- surface fibrous load ment Door beam
Compound layer (.mu.m) texture (Kgf) (mm) Judgement G (For 1 250
1:2 1,000 180 No good Comparison) F (Example) 1 20 1:25 1,020 300
Good
[0076] [Fourth Embodiment]
[0077] An aluminum alloy of Composition 1 shown in Table 4 was
melted by a conventional process and cast to form an ingot with a
diameter of 200 mm. The ingot was subjected to homogenizing heat
treatment at 470.degree. C. for 8 hours and then extrusion at a
temperature of 460.degree. C., an extrusion rate of 5 m/min and an
extrusion ratio of 35 to form two door beams H having a
cross-section shown in FIG. 10B. The extruded door beams H were
immediately cooled by blowing liquid nitrogen and cooled nitrogen
gas and subjected to aging at 130.degree. C. for 12 hours.
[0078] A door beam I for comparison having the same cross-section
was prepared from the aluminum alloy of Compound 2 shown in Table 4
by the same process.
[0079] Table 6 shows the results of the thickness of the
recrystallization surface layer, the aspect ratio of the fibrous
texture, and the three-point bending test at a bending distance of
700 mm of the door beams I and H. As shown in Table 6, although
both door beams I and H satisfy the scope of the present invention
in terms of the thickness of the recrystallization surface layer
and the aspect ratio of the fibrous texture, the door beam I, which
is out of the scope of the present invention in terms of the
composition has a smaller maximum bending load and a smaller energy
absorption compared with the door beam H.
6TABLE 6 Thickness of Aspect recrystal- ratio Maximum lization of
bending Energy surface fibrous load absorption Door beam Compound
layer (.mu.m) texture (Kgf) (kgf .multidot. mm) Judgement I (For 2
30 1:20 1,310 183,300 No good Comparison) H (Example) 1 20 1:20
1,840 265,l00 Good
[0080] The composition and the texture of the door beam in
accordance with the present invention will now be described in more
detail.
[0081] Mg and Zn
[0082] Magnesium and zinc are essential for the aluminum alloy in
accordance with the present invention in order to achieve excellent
mechanical properties. At a magnesium content of less than 0.8% by
weight or a zinc content of less than 4% by weight, the aluminum
alloy does not have the desired strength. At a magnesium content of
more than 1.5% by weight or a zinc content of more than 7% by
weight, the extrudability and elongation of the aluminum alloy
decrease, and the required strength is not achieved. Thus, in the
aluminum alloy in accordance with the present invention, the
magnesium content is set to a range from 0.8 to 1.5% by weight and
the zinc content is set to a range from 4 to 7% by weight.
[0083] Ti
[0084] Titanium is an essential element to form a fine texture in
the ingot. A titanium content of less than 0.005% by weight does
not cause satisfactory formation of the fine texture, whereas a
titanium content of more than 0.3% by weight causes the formation
of huge nuclei because of saturation of titanium in the aluminum
alloy. Thus, the titanium content is set to a range from 0.005 to
0.3% by weight.
[0085] Cu, Mn, Cr and Zr
[0086] These elements cause increased strength of the aluminum
alloy. Further, copper improves stress corrosion crack resistance
of the aluminum alloy. Manganese, chromium or zirconium forms a
fibrous texture to reinforce the alloy. At least one of these
elements is added according to demand. Preferred ranges for these
elements are as follows: 0.05 to 0.6% by weight for Cu, 0.2 to 0.7%
by weight for Mn, 0.05 to 0.2% by weight for Cr, and 0.05 to 0.25%
by weight for Zr. If these elements are added in an amount of less
than their lower limits, these elements will not effectively
contribute to the strength of the aluminum alloy. If a content of
one of the elements is higher than its upper limit, the
extrudability will deteriorate. In particular, copper over the
upper limit will cause deterioration of general corrosion
resistance.
[0087] Incidental Impurities
[0088] The aluminum alloy contains iron as the main component of
the incidental impurities in a relatively large amount. If the
aluminum alloy contains more than 0.35% by weight of iron, coarse
intermetallic crystals form in the casting process, mechanical
strength of the alloy decreases. Thus, the iron content is
controlled to be 0.35% by weight or less.
[0089] Various impurities, derived from the ground metal and the
mediate alloy for the essential elements, are included in the
aluminum alloy. Types of the impurities vary with the used ground
metal and the used mediate alloy. When the sole content of each
impurity other than iron is less than 0.05% by weight and the total
content of individual impurities other than iron is less than 0.15%
by weight, the aluminum alloy has the desired mechanical
properties. Thus, the sole content and the total content of the
impurity are set to 0.05% or less and 0.15%, respectively, by
weight.
[0090] Texture in Extruded Material
[0091] When a thick recrystallization layer is formed on the
surface of the door beam, a rough surface forms in the bending
deformation process. The rough surface functions as a notch and
causes stress concentration. Thus, the rupture of the door beam
will be prompted, and energy absorption is decreased. Since the
aluminum alloy in accordance with the present invention has a thin
recrystallization layer of 50 .mu.m or less, no rough surface forms
and stress concentration is avoidable. Preferably, the
recrystallization layer is not present.
[0092] It is preferable that the crystallites in the fibrous
texture on the surface and inside the alloy have an aspect ratio of
1:20 or more. Although granular crystallites or low-aspect-ratio
crystallites will readily form a rough surface by bending
deformation, crystallites having such a high aspect ratio do not
form a rough surface under a bending deformation condition for the
door beam. Thus, stress concentration is avoided.
[0093] The aspect ratio of the fibrous texture in the present
invention is defined as the ratio of the crystal grain size in the
extruding direction to the crystal grain size in a direction in
which the smallest crystal grain size is observed, in the plane
perpendicular to the extruding direction, and is determined by a
cutting method according to JIS-H0501. That is, a cut sample was
prepared from the center of the loaded section in the inner flange
subjected to the three-point bending test as shown in FIG.
2(A).
[0094] The recrystallization layer on the surface of the extruded
member is formed by the heat, which is generated by large
deformation of the surface in the extrusion process. Thus, the
formation and propagation of the recrystallization layer can be
prevented by decreasing the extrusion temperature, the extrusion
speed, and the extrusion ratio by means of multinozzle extrusion.
Further, the formation and propagation of the recrystallization
layer can be prevented by rapidly cooling only the surface layer of
the extruded member near downstream of the outlet of the extrusion
die.
[0095] Exemplary conditions for producing the aluminum door beam
having the above-mentioned texture are as follows: a homogenizing
heat treatment temperature of 450.degree. C. to 500.degree. C., an
extruding temperature of 400.degree. C. to 500.degree. C., an
extruding rate of 6 to 10 m/min., an extrusion rate of 35 to 70, an
aging temperature of 130.degree. C. to 170.degree. C., and an aging
time of 6 to 12 hours. The temperature rise on the surface of the
extruded member is suppressed by liquid nitrogen and cooled
nitrogen gas blow near the outlet of the extrusion die.
[0096] The cross-section, the composition and the texture in
accordance with the present invention is described above. Buckling
displacement, energy absorption and a displacement without rupture
can be further improved by combining these parameters.
* * * * *