JP3272130B2 - Energy absorbing member and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heat treatment after welding of an energy absorbing member for reducing the impact on passengers in the event of collision of transportation equipment such as automobiles.
The present invention relates to an energy absorbing member made of a Zn-Mg based alloy extruded material and a method for manufacturing the same.

[0002]

2. Description of the Related Art Transportation equipment such as automobiles is required to be safe for passengers. Particularly in automobiles, structures and equipment for ensuring safety for occupants in the event of a collision are required. Specifically, in the event of a collision, the structural material buckles and deforms in an accordion-like manner in the front engine portion or the rear trunk portion, thereby absorbing the energy of the collision and mitigating the impact applied to the occupant in the cabin. It has a structure. Conventionally, cold rolled steel sheets have been used for these structural materials.

[0003] In recent years, there has been a demand for reduction of vehicle weight from the viewpoint of environmental problems and shortening of braking distance at the time of sudden stop.
For this reason, in automobiles, Al or an Al alloy material having a specific gravity as small as about 1/3 of a steel plate has been used for bumpers and other parts. Particularly, the use of an extruded aluminum alloy is being studied because a complicated shape can be easily manufactured as compared with a plate material. Also, the use of Al alloy materials for energy absorbing members conventionally formed of cold-rolled steel sheets has been studied (JP-A-64-67482).
issue).

FIG. 1 is a perspective view showing an energy absorbing member welded to an aluminum alloy bumper. The energy absorbing member 2 is a hollow square pipe-shaped member, one end of which is welded to an Al alloy bumper 1 and the other end of which is attached to a Fe member (not shown). In the case of a light collision, only the bumper 1 absorbs the impact, but in the case of a relatively large collision, the energy absorbing member 1 buckles and deforms in an accordion shape to absorb the energy at the time of the collision.
Thereby, the impact at the time of the collision is reduced, and the safety of the occupant in the cabin can be ensured.

FIG. 2 is a graph showing an example of the relationship between the displacement of the energy absorbing member and the load. As shown in FIG. 2, the compression load fluctuates with the displacement. That is, the compression load first rises to a maximum value, and then fluctuates around a value (average load) lower than the maximum value. The load showing the first maximum value is called an initial load. The initial load can be considered as a load required for deformation, and when a compressive load is applied, buckling deformation is repeated after initial deformation occurs.

Incidentally, the deformation load of the energy absorbing member needs to be larger than the deformation load of the bumper and smaller than the deformation load of the Fe member. Also,
Since the amount of energy absorption of the energy absorbing member is represented by the product of the load and the displacement (load × displacement), in order to increase the amount of energy absorption, the strength of the energy absorbing member must be Fe
It is preferable that the strength is close to the strength of the member.

As a material of the energy absorbing member, Al is used.
-Zn-Mg based alloys are receiving attention. That is, in the case of pure Al and other Al alloys, there is a drawback in using them as energy absorbing members. For example, pure Al and A
Since all the l-Mg alloys have low strength, the effect of alleviating the impact at the time of collision is not sufficient. In addition, it is difficult to extrude hollow Al-Mg-based alloys and Al-Cu-based alloys with a porthole die or the like. Furthermore, in the case of an Al-Mg-Si alloy, the balance between strength and productivity is inferior to that of an Al-Zn-Mg alloy. On the other hand, an Al—Zn—Mg-based alloy has the advantages of being lightweight and high-strength and capable of being thinly extruded and welded, and is suitable as a material for an energy absorbing member.

[0008]

However, Al-
The extruded Zn-Mg alloy has the following problems.
That is, when the Al-Zn-Mg based alloy extruded material is welded, the heat-affected zone softened by welding hardens due to natural aging, cracks occur during buckling deformation, and the effect of reducing impact is reduced. Also, due to natural aging of the heat-affected zone, the initial load also changes with time. Therefore, Al-Zn-Mg
Simply welding a system alloy extruded material to an Al alloy bumper, although exhibiting good energy absorption characteristics in a new vehicle, will deteriorate the energy absorption characteristics several years later, which is not preferable.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an energy absorbing member capable of suppressing a change in initial load and a change in deformation performance of a heat-affected zone due to welding with time, and a method of manufacturing the same. With the goal.

[0010]

An energy absorbing member according to the present invention is made of an extruded Al-Zn-Mg alloy and is buckled by impact energy applied to the other member by being welded to the other member. In the energy absorbing member, the weld and the base material are heat-treated at a temperature of 100 to 250 ° C.

The method of manufacturing an energy absorbing member according to the present invention includes the steps of welding an extruded material of an Al-Zn-Mg alloy to another member, and heating a welded portion of the extruded material and a base material at a temperature of 100 to 250 ° C. And performing a heat treatment.

[0012]

The present inventors conducted various experimental studies in order to suppress the age hardening and the change in initial load due to natural aging after welding of an extruded Al-Zn-Mg alloy. As a result, it was found that by performing heat treatment under appropriate conditions after welding, it is possible to suppress cracking of the heat-affected zone due to welding and temporal changes in the initial load. That is, in the present invention, Al-
The weld portion and the base material of the extruded Zn—Mg alloy are heat-treated at a temperature of 100 to 250 ° C. As a result, cracks in the heat-affected zone and changes over time in the initial load can be suppressed, and good energy absorption characteristics can be maintained over a long period of time. However, when the heat treatment temperature is 100
If the temperature is lower than 0 ° C., precipitation of a GP (Guinier-Preston) zone occurs and the structure becomes the same as that of natural aging, so that there is no effect of suppressing cracking. If the heat treatment temperature exceeds 250 ° C., precipitates of η ′ are formed in the heat-affected zone, so that cracks in the heat-affected zone and changes with time in the initial load during deformation can be suppressed, but the base material is excessively heated. Aging occurs, and the η ′ precipitate becomes coarse, resulting in a significant decrease in strength. Therefore, the heat treatment temperature is set to 100 to 250 ° C.

If the hardness (Hv) of the heat-affected softened portion due to welding after the heat treatment is set to 90% or less of the hardness of the base material, the heat-affected portion is preferentially deformed at the time of collision, and the initial load is reduced. . As a result, the difference between the initial load and the load generated thereafter becomes smaller, and the effect of alleviating the impact further increases. For this reason, it is preferable that the hardness of the heat-affected softened portion be 90% or less of the hardness of the base material, for example, by appropriately setting welding conditions and subsequent heat treatment conditions.

[0014]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples that depart from the scope of the claims.

First, an Al—Zn—Mg alloy having a composition (unit:% by weight) shown in Table 1 below was melt-cast to obtain a billet having a diameter of 155 mm. 470 ° C
After homogenizing at the temperature of 6 hours for 6 hours, the height is 70 m
The extruded material was extruded into a hollow square pipe having a width of 50 mm, a width of 50 mm, and a thickness of 2 mm, and the extruded material immediately after the extrusion was cooled by a fan at a cooling rate of about 300 ° C./min and quenched.

[0016]

[Table 1]

Next, the extruded material was heat-treated at a temperature of 170 ° C. for 6 hours to obtain a T5 heat-treated material, and the length of the extruded material was 1 mm.
It was cut to 20 mm. Then, as shown in FIG. 3, both ends of the extruded material 3 are 150 mm long and 150 m wide.
m, an Al alloy (5083 alloy) plate 4a having a plate thickness of 3 mm
4b was fillet welded into a test body.

The specimen thus obtained was subjected to aging heat treatment at the temperature and time shown in the column of aging conditions in Table 2 below. Then, the hardness (Hv) of the heat-affected zone and the base metal of the test specimen immediately after the heat treatment (immediately after welding in Comparative Example 1) was measured, and a compression deformation test was performed to examine the initial load and the presence or absence of cracks. The specimen after the heat treatment (after welding in Comparative Example 1) was left at room temperature for 30 days, and the hardness of the heat-affected zone of the specimen was measured in the same manner. The presence or absence of cracks was examined. These results are summarized in Tables 2 and 3 below. However, the hardness of the heat-affected zone is, as shown in FIG.
The hardness at a portion separated by 0 mm) was measured and shown as a ratio to the hardness of the base material before the heat treatment (that is, the specific hardness). The specific hardness after the heat treatment is a ratio between the hardness of the base material after the heat treatment and the hardness of the base material before the heat treatment. Further, the compressive deformation test is performed by using an Amsler universal testing machine, applying pressure from the direction shown by the white arrow in FIG. went. And
The initial load was measured, and a value obtained by dividing the initial load by the average load (load ratio = initial load / average load) was obtained. Also,
After the compression deformation test, the presence or absence of cracks was visually inspected.

[0019]

[Table 2]

[0020]

[Table 3]

As is clear from Tables 2 and 3, Comparative Example 1 in which no heat treatment was performed after welding had a very high specific hardness after 30 days compared to the specific hardness immediately after welding, and crush cracking occurred. In Comparative Example 2 in which the heat treatment temperature was as low as 70 ° C., the load ratio was as large as 3.2, so that the effect of reducing the impact at the time of collision was not sufficient. In Comparative Example 2, crush cracking also occurred in the compression deformation test immediately after the heat treatment. In Comparative Example 3, in which the heat treatment temperature was as high as 300 ° C., although the initial load was small and the change in specific hardness with time was small, the base material strength after the heat treatment was low, so that the amount of energy absorption was small. On the other hand, in Examples 1 to 6, the change with time of the hardness of the welded portion was small,
Since no crush cracking occurs and the load ratio is small, good energy absorption characteristics can be maintained over a long period of time.

[0022]

As described above, according to the present invention, A
Since the welded part and the base material of the extruded l-Zn-Mg alloy are heat-treated at a predetermined temperature, it is possible to suppress the temporal change of the hardness of the heat-affected zone due to welding. Therefore, the energy absorbing member according to the present invention has an effect that good energy absorbing characteristics can be maintained for a long period of time.

According to the method of the present invention, Al-Zn-
Since an extruded Mg-based alloy is welded to an Al-alloy bumper or the like, the weld and the base metal are heat-treated at a predetermined temperature, so that the energy absorbing member is lightweight and can maintain good energy absorption characteristics over a long period of time. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an energy absorbing member welded to an Al alloy bumper.

FIG. 2 is a graph showing an example of a relationship between a displacement of an energy absorbing member and a load.

FIG. 3 is a perspective view showing a shape of a test body.

FIG. 4 is a perspective view showing a method for measuring the hardness of the heat-affected softening portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1; Bumper 2; Energy absorption member 3; Extruded material 4a, 4b; Al alloy plate 5; Bead part

Continued on the front page (72) Inventor Takato Fujii 14-1, Chofu Minato-cho, Shimonoseki-shi, Yamaguchi Prefecture Kobe Steel, Ltd. Chofu Works (56) References JP-A-6-227333 (JP, A) 5-47003 (JP, Y2) Jikken Hei 5-47004 (JP, Y2) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22F 1/04-1/057 B60R 19/00-19 / 56

Claims (3)

(57) [Claims] 1. An energy absorbing member made of extruded Al-Zn-Mg based alloy, which is welded to another member and absorbs impact energy applied to the other member by buckling. Characterized by being heat-treated at a temperature of 100 to 250 ° C. 2. The energy absorbing member according to claim 1, wherein the hardness of the weld heat affected softening portion is 90% or less of the hardness of the base material. 3. A step of welding an extruded material of an Al—Zn—Mg alloy to another member, and a step of welding a welded portion and a base material of the extruded material to one another.
Heat treating at a temperature of 00 to 250 ° C.