JPH08170139A - Aluminium-magnesium-zinc-copper type aluminum alloy material having high strength and high extrudability - Google Patents

Abstract

PURPOSE: To produce an Al-Mg-Zn-Cu type Al alloy material excellent in stress corrosion cracking resistance and having high strength and high extrudability by providing an extruded material of specific composition, consisting of Mg, Zn, Cu, Zr, Ti, and Al, with specific recrystallization layers and fibrous structure. CONSTITUTION: A hollow port hole extruded material 1, consisting of intermediate parts 4 and corner parts 5, is composed of an Al-Mg-Zn-Cu type Al alloy material which has a composition consisting of, by weight, 0.5-0.9% Mg, 6.7-9.0% Zn, 0.1-0.4% Cu, 0.05-0.25% Zr, 0.005-0.2% Ti, and the balance Al with inevitable impurities and further containing, if necessary, 0.1-0.4% Ag. Further, recrystallization layers 8, 9, each having a thickness (t) 10% or less the wall thickness 3 and also having <=150μm average grain size, are formed at the external and the internal surface 6, 7 of the intermediate part 4, and the structure in the inner part is formed into fibrous structure 10. Moreover, it is preferable that the minimum width W of the recrystallized structure 13 in the deposition zones 3a to 3d in respective corner parts 5 is regulated to a value 15% or less than the wall thickness 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for automobile bumpers, automobile structural materials and the like, and also for other structural materials and the like. High strength and high extrudability Al-Mg-Zn-Cu.
System aluminum alloy material.

[0002]

2. Description of the Related Art Aluminum extruded materials are lightweight and have excellent energy absorption properties, and are therefore widely used in automobile structural materials and the like which are required to be lightweight and have energy absorption properties. In particular, for automobile bumpers, frame materials, and the like, extruded materials of aluminum alloy are used because lightness and energy absorption are particularly required.

Hollow extrusion includes porthole extrusion and mandrel extrusion. Mandrel extrusion is effective for extruding a cylindrical pipe having a perfect circular shape.
If it is not circular like a square tube, it is difficult to insert the mandrel. For this reason, the mandrel extrusion method is rarely used industrially. On the other hand, in the hollow porthole extrusion method that is industrially used for extruding a rectangular tube-shaped member, recrystallization occurs at the welded portions at the four corners of the rectangular tube.

Extruded sections of automobile parts such as bumpers or automobile structural materials often have a complicated shape having a hollow portion, and unless the alloy has excellent extrudability, it is extremely possible to obtain an extruded material with high accuracy. Have difficulty. Further, since such an extruded material is used as a structural material, it is desired that the alloy has a higher strength, but generally, when the strength of the alloy is improved, the deformation resistance is also increased, and the extrudability is lowered. Will end up. Therefore, even if the strength of the alloy can be improved, it is difficult to make the extruded shape into a complicated shape because the deformation resistance of the alloy is large. As described above, the strength of the alloy and the extrudability have a contradictory relationship in that when one is improved, the other is decreased. Therefore, conventionally, there has been a demand for the development of an alloy having both properties improved, that is, an aluminum alloy having high strength and high extrudability.

[0005]

However, as an alloy used for this kind of conventional application, JIS7003 is used.
Although there is an alloy, this alloy is relatively excellent in extrudability in the 7000 series alloy, but its strength is insufficient when used as a structural material for automobiles. On the other hand, 7,000
Among the type alloys, JIS7075 alloy has high strength, but it is difficult to manufacture an automobile structural material having a complicated shape because of its poor extrudability.

This JIS7003 alloy has Zn:
5.0-6.5% by weight, Mg: 0.5-1.0% by weight,
Cu: 0.2 wt%, Zr: 0.05 wt% to 0.25
It is an aluminum alloy containing wt%, Ti: 0.2 wt%, Mn: 0.3 wt% and Cr: 0.2 wt%.

The present invention has been made in view of the above problems, has strength superior to JIS 7003 alloy, extrudability and stress corrosion cracking resistance are equal to or higher than those of JIS 7003 alloy, and High strength and high extrudability Al-Mg-Zn-C that can be used as a bumper or structural material for automobiles to reduce the weight of automobiles and improve safety
It is an object to provide a u-based aluminum alloy material.

[0008]

A high-strength and high-extrudable Al-Mg-Zn-Cu-based aluminum alloy material according to the present invention comprises Mg: 0.5 to 0.9 wt% and Zn: 6.7 to. 9.0% by weight, Cu: 0.1 to 0.4% by weight, Zr:
A hollow porthole extruded material containing 0.05 to 0.25% by weight and Ti: 0.005 to 0.2% by weight, with the balance being Al and inevitable impurities, and other than the welded part of the extruded material. 1 on each of the outer and inner surfaces of the
A recrystallized layer having a thickness of 0% or less is formed, the inside has a fibrous structure, and the average grain size of the recrystallization is 150 μm or less.

Further, as the composition of the aluminum alloy extruded material, Ag can be contained in an amount of 0.1 to 0.4% by weight in addition to the above components.

Further, a solid or mandrel extruded material is used in place of the hollow porthole extruded material having the above-described composition, and a recrystallized layer having a thickness of 10% or less of the wall thickness is formed on the outer surface of the extruded material. Is formed and has a fibrous structure inside,
The average particle size of the recrystallization may be 150 μm or less.

[0011]

The present inventors conducted various experimental studies to develop an aluminum alloy material having improved properties of both high strength and high extrudability. As a result, it has been found that the strength of the extruded material can be improved without increasing the deformation resistance by increasing the content of Zn in the aluminum alloy. Further, generally, the SCC resistance is deteriorated by increasing the Zn amount, but by increasing the addition amount of Cu and setting the thickness of the surface recrystallized layer to a predetermined value or less, an aluminum alloy has a good It has also been found that SCC resistance can be secured.

The reasons for adding the components and limiting the composition of the high strength and high extrudability aluminum alloy material according to the present invention will be described below.

Mg (magnesium): 0.5 to 0.9
Weight% Mg improves alloy strength by combining with Zn to form MgZn ₂ . To achieve this effect,
The amount of Mg added must be 0.5% by weight or more. On the other hand, M
If the addition amount of g exceeds 0.9% by weight, extrudability and the like will be impaired. Therefore, the content of Mg is 0.5 to 0.9.
Weight% In order to further improve the alloy strength, the Mg content is preferably 0.7 to 0.9% by weight.

Zn (Zinc): 6.7 to 9.0 wt% Zn forms MgZn ₂ and improves alloy strength as described above. In this case, if the amount of Zn added is less than 6.7% by weight, alloy strength cannot be improved, while Z
If the added amount of n exceeds 9.0% by weight, the stress corrosion cracking resistance deteriorates. Therefore, the Zn content is 6.7 to 9.0% by weight. In order to further improve the alloy strength, the Zn content is preferably 7.0 to 9.0% by weight.

Cu (copper): 0.1 to 0.4 wt% Cu improves alloy strength by precipitation strengthening, and improves elongation and stress corrosion cracking resistance. However, if the added amount of Cu is less than 0.1% by weight, the above effect cannot be exhibited. On the other hand, if the addition amount of Cu exceeds 0.4% by weight, the corrosion resistance and hardenability are deteriorated. Therefore, the Cu content is 0.1 to 0.4% by weight. In order to further improve alloy strength and stress corrosion cracking resistance, the content of Cu is preferably 0.1 to 0.2% by weight.

Zr (zirconium): 0.05 to 0.
25 wt% Zr is precipitated as a fine intermetallic compound during the homogenization treatment of the billet, and by refining the crystal grains,
Improves strength, elongation and stress corrosion cracking resistance. If the added amount of Zr is less than 0.05% by weight, the above effect cannot be exhibited. On the other hand, if the added amount of Zr exceeds 0.25% by weight,
Coarse intermetallic compounds crystallize out, and the predetermined alloy strength cannot be improved. Therefore, the Zr content is 0.05 to 0.25% by weight. In order to further improve strength, elongation and stress corrosion resistance, the Zr content is preferably 0.1 to 0.2% by weight.

Ti (titanium): 0.005 to 0.2
Amount% Ti improves the alloy strength by refining the crystal grains during casting. In order to exert this effect, it is necessary to add Ti in an amount of 0.005% by weight or more. On the other hand, if the addition amount of Ti exceeds 0.2% by weight, the above effect is saturated, and a coarse intermetallic compound crystallizes, so that a predetermined alloy strength cannot be obtained. Therefore, the content of Ti is set to 0.005 to 0.2% by weight. In order to further improve the alloy strength, the Ti content should be 0.01
It is preferably 0.04 to 0.04% by weight.

Ag (silver): 0.1 to 0.4 wt% Ag precipitates in the alloy to improve stress corrosion cracking resistance. It is preferable to add the alloy material when it is used in an environment where the corrosive action is severe or when it is used in an environment where a large load stress acts. Ag
If the addition amount of Al is less than 0.1% by weight, the above effect cannot be exhibited, and if it is added in excess of 0.4% by weight, coarse crystallized substances are generated in the alloy, and the predetermined alloy strength is obtained. Can't get Therefore, the content of Ag is set to 0.1 to 0.4% by weight. In order to further improve the corrosion resistance and cracking resistance, the content of Ag is preferably 0.1 to 0.3% by weight.

Next, the reasons for limiting the thickness of the surface recrystallized layer and the average grain size of recrystallization will be described.

FIG. 1 (a) is a sectional view showing an example of the hollow extruded material, and FIG. 1 (b) is an enlarged view showing the sectional structure of the intermediate portion 4 on one side thereof. Further, FIG. 1C is an enlarged view showing a cross-sectional structure of a welded portion which is a corner portion of the hollow extruded material. A welded portion 3 is provided at a corner of the hollow extruded material 1.
a, 3b, 3c and 3d are formed. Figure 1 (b)
As shown in (1), the surface recrystallized structures 8 and 9 are formed on the outer surface 6 and the inner surface 7 of the extruded material due to frictional heat of the extruded material and the like during extrusion.
The inside between the surface recrystallized structures 8 and 9 is a fibrous structure 10.
Has become. Further, in the welded portion shown in FIG. 1C, a recrystallized structure 13 continuing from the outer surface 6 to the inner surface 7 is formed.

In the present invention, the thickness t of the portion occupied by the surface recrystallization structures 8 and 9 shown in FIG.
Keep it below 0%. Further, the average grain size of the recrystallized structures 8 and 9 determined by the cutting method in JIS H0501 is set to 150 μm or less. This is because when the thickness t of the recrystallized layer of at least one of the surface crystal structures 8 or 9 formed on the outer surface 6 and the inner surface 7 of the hollow extruded material 1 exceeds 10% of the wall thickness 3, or Has an average particle size of 1
If it exceeds 50 μm, the stress corrosion cracking resistance is significantly deteriorated and the strength is also reduced. Therefore, the thickness t of each surface recrystallized layer on the outer surface 6 and the inner surface 7 other than the welded portions 3a to 3d is set to 10 of the thickness 3 respectively.
% And the average grain size of the recrystallization is 150 μm.
m or less.

Further, as shown in FIG. 1 (c), the welded portion 3
If the minimum width w of each recrystallized structure 13 in a to 3d exceeds 15% of the wall thickness, the strength of the hollow extruded material decreases and the SCC resistance also deteriorates. Therefore, the minimum width w of each recrystallized structure 13 is preferably 15% or less of the wall thickness.

As shown in FIGS. 1 (b) and 1 (c), the portion sandwiched between the surface recrystallizations 8 and 9 by extrusion becomes a fibrous structure 10 elongated and elongated, but the temperature of the billet is about 10. At a high temperature of 540 ° C., a recrystallized structure is deposited even inside the fibrous structure 10. Further, if the extrusion temperature is 470 to 480 ° C. as in the conventional case, the temperature of the extruded material may exceed 500 ° C. due to frictional heat during extrusion, etc., and recrystallization is formed above the temperature of 500 ° C. The inventors of the present application have found by experiments that the recrystallization becomes coarser when the above is performed.

Therefore, the extrusion temperature is preferably about 450 ° C. so that the extruded material does not exceed a temperature of 500 ° C. The cause of coarsening of the recrystallization is the extrusion rate, the extrusion ratio, the component of the billet, and the like. However, if the extrusion rate is 10 m / min, the recrystallization does not coarsen.

In general, stress corrosion cracking is always a problem in 7000 series aluminum alloys. Therefore, as described above, in the present invention, addition of Zr, Cu and Ag to the aluminum alloy improves stress corrosion cracking resistance. I am trying to

The thickness of the surface recrystallized layer is not constant because it varies depending on the measurement position.
The average thickness at each position may be 10% or less of the wall thickness by observing the intermediate portion and the rear end portion.

The high strength and high extrudability A according to the present invention
The 1-Mg-Zn-Cu-based aluminum alloy material is obtained by homogenizing the billet, extruding the billet, and then performing solution treatment, quenching treatment, and aging treatment in this order.
It can be molded into automobile structural materials. The conditions for homogenization, quenching and aging are 7003
It can be performed under the same conditions as in the case of the alloy.

[0028]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples that depart from the claims of the present invention. FIG. 1A is a schematic view showing a cross-sectional shape when the hollow extruded material 1 is cut in a direction perpendicular to its longitudinal direction. 1B is an enlarged view showing the cross-sectional structure of the intermediate portion 4 on one side of the hollow extruded material 1, and FIG. 1C is the cross-sectional structure of the welded portion of the corner portion 5 of the hollow extruded material 1. FIG.

First, an aluminum alloy billet having the composition shown in Table 1 below was homogenized. in this case,
All billets were homogenized at a temperature of 520 ° C. for 4 hours.

Next, a cylindrical aluminum alloy billet having an outer diameter of 150 mm was extruded at an extrusion speed of 5 m / min, and the side length was 40.0 mm and the wall thickness was 2.0 mm as shown in FIG. A hollow extruded material was produced. Then, after solution treatment was performed at a temperature of 500 ° C., quenching was performed by forced air cooling with a fan. Then, a two-step aging treatment was performed at a temperature of 70 ° C. for 5 hours and at a temperature of 130 ° C. for 12 hours. In addition, the billet at the time of extrusion was extruded at a temperature of 480 ° C.

The test material produced as described above was produced by hollow port hole extrusion, but the characteristics of solid extruded materials are not different.

Comparative example No. 11 is a test material manufactured from the conventionally used JIS7003 alloy.

[0033]

[Table 1]

The method for evaluating the test material, which is a hollow extruded material manufactured as described above, will be described below.

First, regarding the thickness and average grain size of the surface recrystallized layer, as shown in FIG. 1A, the intermediate portion 4 on one side of the hollow extruded material surrounded by the dotted line has a predetermined length in the extruding direction. It was cut out, its cross-section was mirror-polished, and then etched. FIG. 1 (b) is an enlarged view showing the cross-sectional structure of the test material subjected to such treatment. Surface recrystallization structures 8 and 9 are formed on the outer surface 6 and the inner surface 7 of the hollow extruded material, respectively. In this case, the thickness and the average grain size of the surface recrystallized layer were measured for the crystal layer having the larger surface recrystallized structure 8 or 9 on either side. The thickness of the surface recrystallized layer is indicated by the ratio of the thickness of the crystal layer of the surface recrystallized structure 8 or 9 to the thickness between the outer surface 6 and the inner surface 7 of the test material.

Next, in order to evaluate the mechanical properties of the hollow extruded material, a JIS No. 5 test piece used in a tensile test was produced from the test material and evaluated for tensile strength, proof stress and elongation.

The extrudability of the alloy was evaluated by observing the surface properties of the test material after extrusion and the deformation resistance value of the test piece taken from the billet after the homogenization treatment by the high temperature compression test. . The temperature of the test piece in the above test is 500 ° C.

Further, regarding the stress corrosion cracking resistance, an SCC test was carried out by dipping a test piece loaded with a stress of 80% of the proof stress by the three-point supporting method in a boiling chromic acid solution for 360 minutes. The stress corrosion cracking resistance was evaluated by the SCC generation time in this test.

The above test results are shown in Table 2 below.

[0040]

[Table 2]

As shown in Table 2 above, Examples No. 1 to No.
4 has excellent strength as compared with the conventional product, Comparative Example No. 11, and even if the strength is improved, the extrudability and the stress corrosion cracking resistance are equal or higher.

On the other hand, from the results of Comparative Examples No. 1 and No. 2, when the Mg content exceeds 0.9% by weight, the extrudability deteriorates, and conversely, the Mg content is less than 0.5% by weight. Then, it is understood that the alloy strength cannot be improved.

From the results of Comparative Examples No. 3 and No. 4, Zn
When the content of Zn exceeds 9.0% by weight, the stress corrosion resistance deteriorates, while when the content of Zn is less than 6.7% by weight, the alloy strength is not sufficiently improved.

From the results of Comparative Examples No. 5 and No. 6, Cu
When the content of Al exceeds 0.4% by weight, press hardenability is deteriorated, so that no improvement in alloy strength is observed,
On the other hand, when the Cu content is less than 0.1% by weight, the strength is not sufficiently improved and the stress corrosion cracking resistance is deteriorated.

From the results of Comparative Examples No. 7 and No. 8, Zr
It can be seen that when the content of Al exceeds 0.25% by weight, the elongation decreases, and conversely, when the content of Zr is less than 0.05% by weight, the stress corrosion cracking resistance deteriorates.

From the results of Comparative Examples No. 9 and No. 10, T
When the content of i exceeds 0.2% by weight, the alloy strength is not sufficiently improved and the extrudability deteriorates. On the other hand, when the Ti content is less than 0.005% by weight, the extrudability is the same as the conventional one, but it is understood that the alloy strength is not sufficiently improved.

Further, a billet having the composition of Example No. 4 shown in Table 1 above was extruded at various extrusion temperatures to change the state of surface recrystallization, and the yield strength and SCC resistance were evaluated. The results are shown in Table 3 below.

[0048]

[Table 3]

As shown in Examples No. 5 and No. 6 in Table 3, if the extrusion temperature is 500 ° C. or less, the grain size and layer thickness of the surface recrystallization are within the range of the present invention,
Good results were obtained for yield strength and SCC resistance.

On the other hand, as shown in Comparative Examples No. 12 to No. 14, when the extrusion temperature exceeds 500 ° C., the grain size of the surface recrystallization becomes coarse and the ratio of the thickness of the surface recrystallization layer to the wall thickness becomes large. Since it exceeds 10%, both the proof stress and the SCC resistance are deteriorated.

[0051]

As described above, according to the present invention,
JIS 70 conventionally used for automobile bumpers, automobile structural materials, etc. by extruding an aluminum alloy having a predetermined composition to form a predetermined surface recrystallization.
It is possible to manufacture an aluminum alloy material having extrudability and stress corrosion cracking resistance equal to or higher than those of the Al alloy No. 03, and having extremely superior strength to the Al alloy. Further, by using the aluminum alloy material for a bumper of an automobile, an automobile structural material, or the like, it is possible to further reduce the weight of the automobile and improve the safety.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross-sectional shape when a hollow extruded material is cut in a direction perpendicular to its longitudinal direction, and an enlarged view showing crystal structures of one side and one corner thereof.

[Fig. 2] Thickness and yield strength of surface recrystallized layer with respect to wall thickness and S
It is a graph which shows the relationship with CC generation time.

[Explanation of symbols]

 1; Hollow extruded material 2a, 6; Outer surface 2b, 7 of hollow extruded material 2b, 7; Inner surface 3; Similarly wall thickness 3a to 3d; Welded portion 4; Surface recrystallized structure on the outer surface 9; Surface recrystallized structure on the inner surface 10; Fibrous structure inside the wall 13; Recrystallized structure on the welded portion

Claims (4)

[Claims] 1. Mg: 0.5 to 0.9% by weight, Zn:
6.7 to 9.0% by weight, Cu: 0.1 to 0.4% by weight, Zr: 0.05 to 0.25% by weight and Ti: 0.
A hollow porthole extruded material containing 005 to 0.2% by weight and the balance consisting of Al and inevitable impurities, and the outer and inner surfaces of the extruded material other than the welded portion each have a wall thickness of 10% or less. A recrystallized layer having a thickness of 100 μm, a fibrous structure inside, and an average grain size of the recrystallized particles of 150 μm or less. High strength and high extrudability Al—Mg—Zn -Cu-based aluminum alloy material. 2. Mg: 0.5 to 0.9% by weight, Zn:
6.7 to 9.0% by weight, Cu: 0.1 to 0.4% by weight, Zr: 0.05 to 0.25% by weight, Ti: 0.0
A hollow porthole extruded material containing 0.05 to 0.2% by weight and Ag: 0.1 to 0.4% by weight, the balance being Al and inevitable impurities, and a portion other than the welded portion of the extruded material. Characterized in that a recrystallized layer having a thickness of 10% or less of the wall thickness is formed on each of the outer surface and the inner surface thereof, the inside has a fibrous structure, and the average particle diameter of the recrystallization is 150 μm or less. High strength and high extrudability Al-Mg-Zn-
Cu-based aluminum alloy material. 3. Mg: 0.5 to 0.9% by weight, Zn:
6.7 to 9.0% by weight, Cu: 0.1 to 0.4% by weight, Zr: 0.05 to 0.25% by weight and Ti: 0.
A solid or mandrel extruded material containing 005 to 0.2% by weight and the balance Al and unavoidable impurities, and a recrystallized layer having a thickness of 10% or less of the wall thickness is formed on the outer surface of the extruded material. A high-strength and highly extrudable Al-Mg-Zn-Cu-based aluminum alloy material, which is formed, has an internal fibrous structure, and has an average grain size of recrystallization of 150 μm or less. 4. Mg: 0.5 to 0.9% by weight, Zn:
6.7 to 9.0% by weight, Cu: 0.1 to 0.4% by weight, Zr: 0.05 to 0.25% by weight, Ti: 0.0
A solid or mandrel extruded material containing 0.05 to 0.2% by weight and Ag: 0.1 to 0.4% by weight, the balance consisting of Al and unavoidable impurities, and having a wall thickness on the outer surface of the extruded material. A recrystallization layer having a thickness of 10% or less is formed, the inside has a fibrous structure, and the average grain size of the recrystallization is 150 μm or less. -Mg-Zn-Cu based aluminum alloy material.