JPH05132733A - High-strength aluminum alloy for welding - Google Patents

Abstract

PURPOSE: To provide a high strength aluminum alloy for welding in which mechanical strength is improved more than that of the conventional Al alloy for welding.

CONSTITUTION: A high strength Al alloy for welding having a compsn. using Al as a base metal, contg., by weight, 3.5 to 5% Zn, 2 to 3.5% Mg, 0.5 to 1.2% Mn and 0.1 to 0.3% Zr and added with at least one alloy element among Fe, Si, Cr and Ti by ≤0.1% is prepd. This high strength Al for welding having the compsn. maintains the weldability of the conventional Al alloy for welding and whose strength can be increased comparably to that of the conventional high strength Al alloy for nonwelding.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al-Zn-Mg-based high-strength aluminum alloy having excellent weldability and high strength.

[0002]

2. Description of the Related Art In general, high-strength aluminum alloys have the advantage that they have higher mechanical strength than other metals with respect to the same weight. Therefore, they are structural materials for aircraft that require weight reduction and high strength. It is also widely used as a material for military weapons. However, since such a high-strength aluminum alloy has poor weldability, its use is limited in the fields requiring welding such as materials for military vehicles or materials for gas storage. There is.

Therefore, as a result of research and development of an aluminum alloy having excellent weldability and high strength, Al 7
Aluminum alloys for welding, such as 017, Al 7039 and Al 2519, have become known, but Al 7017, which has the highest strength among these alloys, has a yield strength of 420 MPa and a tensile strength of about 480 MPa. The current situation is that the pressure does not exceed 500 MPa.

At present, including the Al 7017,
Most of the commonly used aluminum alloys for welding are Al--Zn--Mg based precipitation hardening alloys.
It has a composition in which 4 to 5% of Zn and 1 to 3.5% of Mg are contained as a base of l and 0.1 to 0.4% of Cr and Mn are added in some cases, and the main strengthening effect is Zn and Mg. It is known that this is due to the formation of precipitates.

On the other hand, recently, a high strength aluminum alloy such as Al 7075 or Al 7050 has been developed as a non-welding aluminum alloy, and it has a yield strength and a tensile strength of 500 MPa or more, so that it is inferior in strength to these alloys. Welding aluminum alloys such as Al 7017, which have a
rength aluminum) and is used as an aluminum alloy for welding.

[0006]

However, in the case of such an aluminum alloy for welding, when it is used as a material for a welded structure of a high-speed train or a vehicle, which is inevitably required to have high strength and light weight, it is a non-welding high alloy. Since the strength is inferior to that of the aluminum alloy, the volume of the required material is increased to withstand the required strength, the weight of the structure is increased, and the fuel consumption is increased.

As a result, the inventors of the present invention have conducted extensive research in order to solve such problems, and as a result, intend to provide the following high-strength aluminum alloy for welding. That is, an object of the present invention is to provide a high-strength aluminum alloy for welding which can be used as a material for a welded structure of a high-speed train or a military vehicle by further improving mechanical strength as compared with a conventional aluminum alloy for welding. Is.

[0008]

In order to achieve the object of the present invention, the high-strength aluminum alloy for welding according to the present invention uses Al as a base metal and Zn3.5-5.
wt%, Mg2-3.5 wt%, Mn0.5-1.2 wt%,
Zr 0.1 to 0.3 wt% is contained, and at least one alloy element of Fe, Si, Cr and Ti is added in an amount of 0.1 wt% or less.

In the aluminum alloy for welding having such a composition, the conventional Al--Zn--Mg system is used as a basic composition, and M of the transition metal is used as a strengthening element for further improving the strength.
A small amount of n and Zr is added to induce generation of fine Mn dispersed particles (dispersoids) and Zr dispersed particles in the alloy structure, thus maintaining the weldability and quenching sensitivity of conventional welding alloys almost as they are. It is possible to increase the strength of a welding aluminum alloy to the strength level of a non-welding aluminum alloy such as Al 7075 or Al 7050 with almost no reduction in elongation.

The components of the aluminum alloy having such a composition and the limited ranges of the contents of the components will be described as follows. First, Zn and Mg are Al for welding.
It is used as the main strengthening element in -Zn-Mg alloys, but high strength is maintained only when Zn / Mg is about 2 or slightly less than 2, and at the same time, the amount of Zn + Mg becomes 8.5 wt% or less. Only then will good weldability appear.

Mn is added to supplement the strengthening effect of the main strengthening elements Zn and Mg, and a high strength characteristic of about 500 MPa can be obtained only by the precipitates of Zn and Mg. Therefore, Mn is 0.5 to 1.2 w
Add t% to generate Mn dispersed particles. In particular, the Mn is the most important element among the elements of the alloy according to the present invention, and it has a role of forming fine Mn dispersed particles of 0.1 to 0.4 μm in the alloy structure and hindering the movement of dislocations (pinning). actio
n) increases the strength of the alloy. on the other hand,
The Mn-dispersed particles interact with dislocations to homogenize the distribution of slip bands, thereby preventing the reduction of the draw ratio.

Zr is an aluminum alloy,
It is an element that has a strong effect on recrystallization suppression and grain refinement, and produces fine Zr dispersed particles as with Mn.
When the amount of Zn + Mg approaches 8.5 wt%, the weldability is slightly deteriorated. Therefore, as a countermeasure against these, 0.1 to 0.3 wt% of Zr, which is an element that improves the weldability, is added. Further, Fe and Si form a second phase having a relatively large crystal size in the Al-Zn-Mg-based alloy, and as a result, reduce ductility.

Cr reduces the weldability but increases the strength of the alloy. And, Ti reduces the free precipitation zone in the alloy. The high-strength aluminum alloy for welding according to the present invention having such a composition is commercialized by heat treatment so as to obtain the highest strength. Then, in the high-strength aluminum alloy for welding according to the present invention, the weldability of the conventional aluminum alloy for welding is maintained as it is, and the strength is improved to the level of the strength of the non-welding high-strength aluminum alloy. Therefore, when it is used as a structural material for high-speed trains and vehicles, the weight of the vehicle body can be significantly reduced as compared with the conventional case, and the fuel cost can be reduced. Further, there is an effect that it can be widely applied as a structural material in the industrial field that requires excellent weldability, high strength and light weight.

[0014]

EXAMPLES The results of comparison with the examples of the present invention and comparative examples will be described in detail below. A sample of the aluminum alloy according to the present invention having the composition shown in Table 1 (Example 1
~ 3) were manufactured and subjected to two aging heat treatments. In the case of a normal high-strength aluminum alloy, the highest strength is obtained by performing the primary aging heat treatment, but the samples according to Examples 1 to 3 obtain the highest strength only by the conventional primary aging heat treatment. Since it is difficult, it is preferable to perform the aging heat treatment twice. That is, the sample was solution-treated at 420 ° C. to 500 ° C. for 1 to 5 hours, then rapidly cooled in water, and subjected to a primary aging heat treatment at 80 ° C. to 100 ° C. for 8 to 12 hours. Then, a second aging heat treatment was performed at 120 to 150 ° C. for 10 to 18 hours. It should be noted that Table 1 shows the first embodiment.
3 to 3, the chemical compositions (wt%) of three comparative examples (conventional aluminum alloys for welding) are also shown.

[0015]

[Table 1]

After that, the mechanical properties of the specimens of Examples 1 to 3 after the secondary aging heat treatment, the above-mentioned comparative examples and Al 7075 which is a conventional non-welding high strength aluminum alloy were measured and the results were obtained. Is shown in Table 2.

[0017]

[Table 2]

As is apparent from Table 2, the aluminum alloy for welding according to this example is remarkably excellent in mechanical strength as compared with the conventional aluminum alloy for welding. It can be seen that it has almost the same level of strength as Al 7075. On the other hand, in order to compare and see the weldability of the aluminum alloy for welding according to the present Examples 1 to 3, the base material and the welded portion of the sample of the present example and the comparative example sample under the following welding conditions. Was measured and the results are shown in Table 3.

Welding conditions Welding method: Gas methanol arc welding Current: 220 to 240 A Voltage: 30 V Wire speed: 20 to 30 mm / sec Welding rod: Al 5316 Used electrode: DCRP base metal thickness: 10 mm

[0020]

[Table 3]

As is clear from Table 3, the aluminum alloy for welding according to this example has a higher tensile strength than the conventional aluminum alloy for welding (comparative example), and the yield strength and the draw ratio are almost the same or slightly higher. Therefore, when viewed as a whole, it is understood that the aluminum alloy for welding according to this example is superior in weldability to the conventional aluminum alloy for welding.

[0022]

As described above, the high-strength aluminum alloy for welding according to the present invention is remarkably superior in mechanical strength and weldability to the conventional aluminum alloy for welding, and has high strength for non-welding. Aluminum alloy Al 7
Since it has almost the same strength as 075 alloy, it has an effect of being able to supply an aluminum alloy structural material which is remarkably superior to the conventional one applied to a wide range of industrial fields including high-speed trains and various vehicles.

Claims (1)

[Claims] 1. Aluminium-based Zn3.5-5 wt%, Mg
2-3.5 wt%, Mn0.5-1.2 wt%, Zr0.1-0.
A high-strength aluminum alloy for welding, containing 3 wt% and containing at least one element of Fe, Si, Cr and Ti in an amount of 0.1 wt% or less.