JPH11302763A - High strength aluminum alloy excellent in stress corrosion cracking resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an aluminum alloy excellent in strength, toughness, stress corrosion cracking resistance and extrudability and to provide a method for producing it. SOLUTION: This aluminum alloy is the one in which an aluminum alloy having a compsn. contg., by weight, 6.0 to 8.5% Zn, 0.7 to 1.0% Mg, 0.05 to 0.20% Cu, <=0.30% Mn, <=0.20% Cr, 0.20 to 0.30% Zr, 0.01 to 0.05% Ti, and the balance Al with inevitable impurities, in which, as the impurities, <=0.20% Fe and <=0.10% Si are regulated is extruded and is thereafter subjected to two-stage artificial aging treatment, by which it has >=95% fibrous structural ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy used for structural members.

[0002]

2. Description of the Related Art Extruded aluminum alloys are widely used for structural members such as automobiles, railway vehicles, and house building materials for the purpose of weight reduction and the like. For example, 6N01,
7003, 7N01 alloy and the like correspond.

[0003]

In order to improve the fuel efficiency of automobiles and the like by reducing the weight of parts, the conventional 6N01, 70
With the 03, 7N01 alloy and the like, the strength was insufficient and it was difficult to significantly reduce the weight. Further, there is also a problem that the stress corrosion cracking resistance is poor and the reliability as a structural member is poor. An object of the present invention is to provide an aluminum alloy excellent in strength, toughness and stress corrosion cracking resistance in order to solve these problems.

[0004]

Means for Solving the Problems The main components of the aluminum alloy for structural members are Zn and Mg. When the amount of Zn and Mg is increased, the strength is improved, but on the contrary, the extrudability and toughness are deteriorated. That is widely known. However, the present inventors changed the amounts of Cu, Mn, Cr, Zr, Fe, and Si in addition to the components of Zn and Mg, and evaluated various alloys. It has been found that an aluminum alloy having a higher strength than an aluminum alloy and a metal structure of a fibrous structure and having excellent toughness and stress corrosion cracking resistance can be obtained.

[0005] Mg greatly contributes to strength improvement by solid solution hardening and formation of an intermetallic compound with Zn. However, since the atomic radius is different from that of aluminum, if the addition amount is too large, the distortion of the crystal lattice increases, and the deformation resistance decreases. Extrusion processability deteriorates. Since Zn has an atomic radius close to that of aluminum, there is a relatively small increase in deformation resistance with respect to the added amount, and the strength can be improved without lowering the extrusion workability. Corrosion cracking property becomes worse. Therefore, considering other additive components described later, Zn: 6.0 to 8.5 wt%, Mg:
0.7 to 1.0 wt% is optimal. Cu can reduce the potential difference between the crystal grain boundary and the inside of the crystal grain and improve the stress corrosion cracking resistance, but if too much, the corrosion resistance deteriorates, so Cu: 0.0
The range of 5 to 0.20 wt% is good. Zr has an effect of converting a metal structure into a fibrous structure. When tensile bending stress acts on a material, Zr disperses a component force in a bending direction applied to a crystal grain boundary, thereby significantly improving stress corrosion cracking resistance. In addition, coarsening of recrystallization which is likely to occur on the surface of the extruded material can be prevented. The proper range at that time is Zr: 0.20 to 0.30 wt.
%. Mn and Cr also have the effect of refining the crystal grains, but as they are added, they become knitted, so that Mn: 0.30
wt% or less, and Cr: 0.20 wt% or less. Fe,
Si is also incorporated as an impurity in the process of refining and casting aluminum, but Fe: 0.15 wt% or less, Si:
It has also been found that toughness is deteriorated unless the content is 0.10 wt% or less.

Next, a manufacturing method will be described. A cylindrical billet is cast using the aluminum alloy according to the present invention, and then homogenized at 440 to 480 ° C. for 10 to 20 hours. The billet is extruded by an extrusion press using a conventional method. The preheating temperature of the billet is preferably 400 to 470 ° C. If the temperature is lower than 400 ° C., the deformation resistance increases, and the extrusion becomes worse.
If the temperature exceeds 0 ° C., the material becomes brittle, the toughness is deteriorated, the recrystallized grains are coarsened, and the stress corrosion cracking resistance is reduced. The obtained extruded material is subjected to two-stage artificial aging at 80 to 160 ° C.

[0007] The extruded profile obtained by the above-mentioned production has a fibrous structure area ratio of 95% in the cross-sectional direction.
As a result, an inexpensive extruded material having high strength, excellent toughness, excellent stress corrosion cracking resistance and surface properties, and good extrudability was obtained.

[0008]

EXAMPLES Examples of aluminum alloys according to the present invention will be described below in comparison with conventional alloys. In Table 1, alloys A and B show examples of alloys according to the present invention, C, D and E show conventional alloys, and especially E alloy is an aluminum alloy corresponding to JIS7003. Table 2 shows the evaluation results of the profiles obtained by extruding the rectangular pipe having the external dimensions of 45 mm × 45 mm and a thickness of 3 mm shown in FIG. Tensile strength, 0.
The 2% proof stress and elongation were measured based on JIS Z 2241. The toughness was measured by applying a load with a hemispherical punch shown in FIG. 2, taking a displacement (S) -load (F) curve at that time, measuring the integrated value, and setting the value of JIS7003 alloy to 10
The index is set to 0. In the case of a, when the toughness is poor, a crack occurs in the material at a stage where the displacement is relatively small, and the load is rapidly reduced. JIS H 8711 for stress corrosion cracking resistance
Was immersed in a mixed aqueous solution of CrO ₃ , K ₂ Cr ₂ O ₇ , and NaCl at a liquid temperature of 50 ° C., and the time until crack generation was measured. The fibrous structure area ratio was measured by observing the structure of the cross section of the shaped material. The extrusion processability was represented by an index evaluation where the maximum extrusion speed capable of maintaining the appearance quality and shape was alloy E100.

Table 1

Table 2

[0011]

As shown in the results of Table 2, the profile extruded under the predetermined conditions using the alloy according to the present invention has strength,
Excellent in toughness, responsiveness, corrosion cracking and extrusion workability.

[Brief description of the drawings]

FIG. 1 shows an example of a cross-sectional shape of an extruded member using an aluminum alloy according to the present invention.

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

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

[Explanation of symbols]

 1 ····· Test material 2, 2 '··· Upper jig for fixing the test material 3 ····· Lower jig for fixing the test material 4 ······ Punch for applying load to the test material (a) ··· Displacement-load diagram for conventional alloy (b) ···· Displacement-load diagram for alloy of the present invention

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 630 C22F 1/00 630B 630A 640 640A 691 691B

Claims (1)

[Claims] 1. Zn: 6.0-8.5 wt%, Mg: 0.
7 to 1.0 wt%, Cu: 0.05 to 0.20 wt%, M
n: 0.30 wt% or less, Cr: 0.20 wt% or less, Z
r: 0.20 to 0.30 wt%, Ti: 0.01 to 0.05
wt%, with the balance being Al and unavoidable impurities, Fe: 0.20 wt% or less, Si: 0.2 wt%.
Extrusion processing of aluminum alloy of 10 wt% or less,
An aluminum alloy characterized by having a fibrous structure ratio of 95% or more by two-stage artificial aging treatment at 80 to 160 ° C thereafter.