JPH09268342A - High strength aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve toughness and stress corrosion cracking resistance by specifying the composition of contained elements. SOLUTION: This alloy has a composition which consists of, by weight, 7.0-9.0% Zn, 1.5-2.0% Mg, 0.2-0.4% Cu, 0.1-0.5% Mn, 0.05-0.3% Cr, 0.1-0.2% Zr, 0.01-0.05% Ti, and the balance Al with impurities and in which the contents of Fe and Si as impurities are limited to <=0.15% and <=0.1%, respectively. Although an extruded shape with sufficiently high strength can be obtained by using the alloy of this composition even by the conventional method, it is preferable that, in order to improve toughness and stress corrosion cracking resistance to a greater extent, the extruded shape is reheated to 400-470 deg.C, cooled at a rate of >=1000 deg.C/min, and tempered at 80-160 deg.C for 10-72hr. The resultant extruded shape can be provided with >=90% proportion of fibrous structure in a cross section.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aluminum alloy used for structural members.

[0002]

2. Description of the Related Art Extruded aluminum alloys are used as structural members for vehicles under the demand of weight reduction. For example, JIS for automobile bumper reinforcements
7003 alloy and JIS 7075 alloy are used for railway vehicles.

[0003]

[Problems to be Solved by the Invention] However, JIS70
03 alloy has insufficient strength, while JIS 7075
Although high strength can be obtained with alloys, not only does toughness deteriorate extremely, but in the field of vehicle parts such as bumper reinforcements, side door beams, side members, etc. I had the problem that it was not the target. In the field of these vehicle parts,
In order for the weight reduction of the vehicle to directly affect the improvement of fuel economy,
While smaller size is required by using higher-strength aluminum material, improvement of shock absorption by using aluminum material with excellent toughness is very important from the viewpoint of safety for passenger protection. There is. Accordingly, the present invention is to provide an aluminum alloy having high strength and excellent in toughness, stress corrosion cracking resistance and extrusion processability, and a method for producing the same.

[0004]

In an aluminum alloy for extrusion molding, a high strength alloy can be obtained by adding Mg, Zn and Cu, but it is widely inversely proportional to deterioration of extrusion processability and toughness. It is known. However, as a result of trial-evaluating various alloys by changing the amounts of components of Mn, Cr, Zr, Fe and Si in addition to the components of Mg, Zn and Cu, the present inventor has found that the strength is 500 MPa within a certain composition range. (Hereinafter, 0.2% proof stress unless otherwise specified) was obtained, and it was revealed that the toughness, stress corrosion cracking resistance and extrusion processability were excellent. The contents will be described below.

Mg and Zn are added main components of a high-strength aluminum alloy, which can be expected to improve strength by forming an intermetallic compound. Although Mg makes a large contribution to the improvement of strength,
It becomes a factor that significantly impairs the extrusion processability. Zn contributes to the strength improvement without relatively lowering the extrudability, but Mg
If the addition ratio to is higher than a certain level, the stress corrosion cracking resistance is significantly reduced. Therefore, when combined with other additive components described later, the strength is about 500 MPa.
Zn: 7.0 to 9.% in order to secure the characteristics excellent in contradictory toughness, stress corrosion cracking resistance, and extrusion processability while maintaining the above-mentioned values.
0 wt% (hereinafter abbreviated as%), Mg: 1.0 to 2.0%
Is the best. Cu can be expected to undergo solid solution hardening in an aluminum alloy, and can also improve stress corrosion cracking resistance by relaxing the potential difference between the crystal grain boundary portion and the inside of crystal grains. On the other hand, if the addition amount is too large, it causes the potential difference corrosion between Cu and Al. Therefore, Cu: 0.2-
It was selected to be 0.4%. Mn, Cr, and Zr have an effect of refining crystal grains within a certain range, and can improve toughness and stress corrosion cracking resistance without lowering extrusion processability. As a result of various trial evaluations, Mn: 0.1 to 0.5%, Cr: 0.05 to 0.3
%, Zr: 0.1 to 0.2%. Fe and Si
Is a component that is usually mixed as an impurity in the process of refining and casting aluminum, but Fe: 0.15% or less,
It was also clarified that if the content of Si is not more than 0.1%, the toughness is reduced in each case.

Using the aluminum alloy adjusted in the above range of components, it is possible to obtain a sufficiently high-strength aluminum extruded profile even by a conventional heat treatment after billet casting and extrusion processing. In order to maximize the characteristics of the aluminum alloy according to the present invention, the manufacturing conditions described below are good. A cylindrical billet was cast using the aluminum alloy according to the present invention, and then cast at 440 to 480 ° C. for 10 hours.
Homogenize for ~ 20 hours. The billet heating temperature during extrusion is preferably 400 to 450 ° C. Extrusion workability is poor at 400 ° C. or lower, and recrystallization becomes coarse at 450 ° C. or higher to reduce stress corrosion cracking resistance. Even if artificial aging treatment is carried out as it is after extrusion, an aluminum extruded profile excellent in strength, toughness, stress corrosion cracking resistance and extrusion processability can be obtained, but toughness and stress corrosion cracking resistance are further improved. The extruded profile is reheated to 400 to 470 ° C., then cooled at a rate of 1000 ° C./min or more, and then 80 to 1
It is preferable to perform tempering treatment at 60 ° C. for 10 to 72 hours.
The extruded profile produced in this manner can provide an aluminum extruded profile having an area ratio of the fibrous structure of 90% or more in the cross section of the extruded profile and having excellent toughness and stress corrosion cracking resistance.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an aluminum alloy according to the present invention will be described in comparison with a conventional one. Alloy A shown in Table 1,
B shows an example of the amount of the additive component according to the present invention, and comparative alloy C,
D is for confirming the effect of the present invention, and comparative alloy E is an aluminum alloy corresponding to JIS7003. The extruded profile shown in Table 2 is 45 mm × 45 shown in FIG.
The evaluation results of a material obtained by extruding a square pipe having a sectional shape of mm and a thickness of 2 mm are shown. The meaning of the symbol is, for example, "A-
(1), A indicates that alloy A was used, and the subscript (1) is a cylindrical billet having a diameter of 204 mm cast and extruded using a billet homogenized at 460 ° C. for 12 hours. It shows that the artificial aging treatment of 90 ° C. × 6 hours + 150 ° C. × 10 hours was performed after extrusion processing at a temperature (billet heating temperature) of 440 ° C., and the subscript (2) was the same as (1) until extrusion processing. After that, extruded profile is 460 ℃
After being heated for 1 hour, rapidly cooled with water and cooled to room temperature, artificial aging (tempering) treatment is performed at 90 ° C. × 6 hours + 150 ° C. × 24 hours.

Next, a method for evaluating material properties will be described. Tensile strength, 0.2% proof stress, and elongation are measured based on JISZ2241, and toughness is punched with a hemispherical punch as shown in FIG. 2, and displacement (S) -load (load) at that time is applied. F) Taking the curve results in the graph shown in FIG.
(A) shows an example in which when the toughness is poor, material cracking occurs on the way and the load sharply decreases. (B) is an example of good toughness. As an evaluation method, the integrated value obtained from the (S)-(F) curve was measured and E-using JIS7003 was used.
The value of (1) was set to 100 and indexed. The resistance to stress corrosion cracking was evaluated according to JIS H8711, but the corrosion accelerator used was a mixed solution of CrO ₃ , K ₂ Cr ₂ O ₇ and NaCl, and the solution was immersed at 90 ° C. and the time until cracking was measured. . The fibrous structure area ratio was measured by subjecting the extruded shape member to mirror polishing and then etching with an aqueous NaOH solution to measure the area ratio.

[0009]

As is clear from the results shown in Table 2,
The alloys A and B according to the present invention, which are extruded and subjected to a predetermined heat treatment, have high strength, yet exhibit excellent toughness and stress corrosion cracking resistance. Also in terms of extrusion processability, when the cross-sectional shape of FIG. 1 is directly extruded with a 3000 ton press, alloys A and B are 10 to 12 m /
Minute extrusion rates were obtained, with alloy C at 1-2 m / min and alloy D at 4-5 m / min.

[0010]

[0011]

[Brief description of drawings]

FIG. 1 shows an example of a cross section of an extruded profile using an aluminum alloy according to the present invention.

FIG. 2 shows a schematic diagram of a toughness evaluation method.

FIG. 3 shows a displacement (S) -load (F) curve in toughness evaluation.

[Explanation of symbols]

1 ・ ・ ・ ・ Specimen material 2, 2 '・ ・ ・ Upper jig for fixing specimen material 3 ・ ・ ・ ・ ・ ・ Jig for fixing specimen material 4 ・ ・ ・ ・ Load on specimen material Punch that applies force (a) ...- Example of displacement-load curve for materials with poor toughness (b) ...- Example of displacement-load curve for materials with good toughness

Claims (2)

[Claims] 1. Zn: 7.0 to 9.0 wt%, Mg:
1.5-2.0 wt%, Cu: 0.2-0.4 wt%,
Mn: 0.1-0.5 wt%, Cr: 0.05-0.3
wt%, Zr: 0.1 to 0.2 wt%, Ti: 0.01
An aluminum alloy having a content of ˜0.05 wt%, the balance being Al and unavoidable impurities, and Fe: 0.15 wt% or less and Si: 0.10 wt% or less. 2. After extrusion, heating to 400 to 470 ° C., cooling to 50 ° C. or less at a rate of 1000 ° C./min or more,
The aluminum alloy according to claim 1, which has a fibrous structure ratio of 90% or more by performing artificial aging treatment at 80 to 160 ° C. thereafter.