KR920007936B1 - High strensth al alloy with good weldability - Google Patents

Abstract

This alloy of which composition is based with Al-Zn-Mg system for welding has high strength. The alloy comprises aluminum matrix and 3.5-5 wt.% zinc, 2-3 wt.% mgnesium, 0.5-1.2 wt.% manganese, 0.1- 0.3 wt.% zirconium and 0.1 wt.% Fe, Si, Cr, Ti etc. as a trace elements. The high strength alloy is lighweight and used for structural materials of a high speed train etc..

Description

High Strength Aluminum Alloy for Welding

The present invention relates to a high-strength aluminum alloy for welding Al-Zn-Mg-based welding having excellent weldability and high strength.

In general, high-strength aluminum alloy is widely used as a structural material for military and military materials requiring weight reduction and high strength due to its high strength-to-weight ratio.

However, such a high-strength aluminum alloy has a problem in that its use is limited in a field requiring welding such as a vehicle structural material or a gas storage material because of poor weldability.

Accordingly, as a result of research efforts to develop an aluminum alloy having excellent weldability and high strength, welding aluminum alloys such as Al 2517 and Al 2519, including Al 7017 and Al 7039, are known, but Al having the highest strength among these alloys is known. In the case of 7017, the yield strength is 420 MPa and the tensile strength is about 480 MPa, which does not exceed 500 MPa.

Al-Zn-Mg-based precipitation hardening alloys based on Al as the Al-Zn-Mg-based precipitation hardening alloys, including Al 7017, are generally used, and contain Zn 4-5% and Mg 1-3%. In some cases, Cr and Mn are added in an amount of about 0.1-0.4%, and the main strengthening effect is known to be due to the formation of precipitates by Zn and Mg.

On the other hand, high-strength aluminum alloys such as Al 7075 and Al 7050, which are known as non-welding aluminum alloys, exhibit yield strength and tensile strength of approximately 500 MPa or more, and thus welding aluminum alloys such as Al 7017 having lower strength than those of these alloys are conventional. It is classified as medium strength aluminum alloy [I. J. Polmear, The J. of the Australian Inst. of Metals. Vol. 17 (1972) p. 1].

Therefore, in the case of using the conventional welding aluminum alloy as a material for welding high-speed trains or vehicles requiring high strength and light weight, the weight increases due to the increase in volume compared to the high-strength aluminum alloy for non-welding. There is a problem that greatly increases the consumption of fuel.

Accordingly, the present invention has been made in view of the problems of the conventional aluminum alloy for welding, and an object thereof is to provide a high strength aluminum alloy for welding exhibiting improved strength of the existing high strength aluminum alloy level.

In particular, the high-strength aluminum alloy for welding of the present invention is based on the existing Al-Zn-Mg system as a basic composition by adding a small amount of the transition metal Mn and Zr as a reinforcing element for the direction of strength and fine Mn dispersed particles in the alloy structure ( dispersoid) and Zr dispersion particles are produced, which maintains the weldability and sensitization sensitivity of conventional welding alloys, while increasing the strength to the strength level of Al 7075 or Al 7050 alloys without significantly decreasing elongation. .

The composition of the present invention is based on aluminum as a base metal, Zn 3.5-5wt%, Mg 2-3wt%, Mn 0.5-1.2wt%, Zr 0.1-0.3wt% and minor alloys such as Cr, Fe, Si and Ti The element is added at 0.1 wt% or less.

The reason for limiting the content of the alloy component and each component of the present invention is as follows.

First, Zn and Mg act as main reinforcing elements in welding Al-Zn-Mg based alloys, and the high strength is maintained only when the ratio of Zn to Mg is about 2 or less, while Zn + Mg is less than 8.5wt% It shows good weldability.

Mg is added to supplement Zn and Mg strengthening effects, which are the main strengthening elements, and it is not possible to obtain high strength characteristics of about 500 MPa using Zn and Mg precipitates alone, so 0.5-1.2wt% is added to generate Mn molecular particles.

In particular, Mn is the most important component of the alloying elements of the present invention to increase the strength of the alloy by forming a fine Mn dispersed particles of 0.1-0.4㎛ size in the alloy structure to prevent the movement of dislocations (Pinning actin) Meanwhile, the Mn dispersed particles interact with dislocations to homogenize the distribution of slip bands, thereby preventing a decrease in elongation.

Zr is an element that has a strong effect on recrystallization inhibition and grain refinement in aluminum alloys. Like Zn, Zr produces fine Zr dispersed particles. Especially, when Zn + Mg amount approaches 8.5wt%, weldability is slightly reduced. 0.1-0.3 wt% of Zr which is an element which improves weldability is added.

The alloy of the present invention having such a composition is heat-treated and commercialized to obtain the best strength.

The high strength aluminum alloy for welding of the present invention maintains the weldability of the conventional welding aluminum alloy almost intact while being used as a structural material for vehicles including high speed trains as the strength is improved to the level of the high strength aluminum alloy for welding. There is an effect that can save fuel due to the weight reduction of the vehicle body, as well as can be widely used as a structural material of various industrial fields requiring excellent weldability, high strength and light weight.

Hereinafter, embodiments of the present invention are as follows.

EXAMPLE

The specimen of the present invention having the composition shown in Table 1 below was prepared and subjected to two-stage aging treatment. In general, high strength aluminum alloys may be subjected to one-stage aging heat treatment to obtain the highest strength. However, the specimen of the present invention was subjected to two-stage aging heat treatment because the maximum strength could not be obtained by the conventional one-stage aging heat treatment alone. That is, the specimens were solution-treated at 420-500 ° C for 1-5 hours, quenched in water, and then subjected to one-stage aging treatment at 80-100 ° C for 8-12 hours, and the final aging treatment was performed at 120-150 ° C for 10-hour. It carried out for 18 hours.

TABLE 1

The mechanical properties of the specimens subjected to the two-stage aging heat treatment are shown in Table 2 below.

TABLE 2

As shown in Table 2 above, it can be seen that the embodiment specimen of the present invention is much superior to the conventional welding aluminum alloy in mechanical properties, that is, strength, and is similar to the strength of Al 7075, which is a high-strength aluminum alloy. Can be. On the other hand, in order to determine the weldability of the embodiment of the present invention, the mechanical properties of the welded part was measured under the following welding conditions, and the measurement results are shown in Table 3 below.

Comparative specimens of Table 3 are also welded under the same welding conditions as the specimens of the present invention.

[Welding condition]

Welding Method: Gas Metal Arc Welding

Current: 220-240A

Voltage: 30 V

Wire Speed: 20-30mm / sec

Welding Rod: Al 5356

Electrode used: DCRP

Base material thickness: 10㎜

TABLE 3

According to the above Table 3, the sample of the present invention exhibits a higher tensile strength and yield strength than the conventional welding aluminum alloy (comparative example), and the elongation is slightly lower than that of the comparative sample. Inventive Examples By maintaining the elongation of the specimen to 9-10%, it is not a problem for commercial applications. In addition, the yield strength and the tensile strength of the welded portion with respect to the specimen of the embodiment of the present invention showed almost the same value as that of the comparative specimen, and the alloy of the present invention is weldable as compared with the conventional welding aluminum alloy. It can be seen that the strength of the base material was improved with little deterioration.

In summary, it can be seen that the high strength aluminum alloy for welding of the present invention is superior in strength compared to the conventional welding aluminum alloy, and the strength of the Al 7075 alloy having the highest strength as the non-welding high strength aluminum alloy. In addition to showing a similar level, the weldability is almost the same as that of other conventional welding aluminum alloys, and is suitable as a structural material requiring high strength and weldability at the same time.

Claims (1)

Based on Al, Zn 3.5-5wt%, Mg 2-3wt%, Mn 0.5-1.2wt%, Zr 0.1-0.3wt%, Fe, Si, Cr and Ti, etc. are added to 0.1wt% or less High strength aluminum alloy for welding.