JPH06226455A - Resistance welding method for al-li alloy - Google Patents

Abstract

PURPOSE:To execute the resistance spot welding of Al-Li alloy having less defect of blowhole, undeposited part, etc., by strenghtening welding pressure in the course of applying electricity for spot welding. CONSTITUTION:Al-Li alloy material with Li content of 1-4% is spot welded. Applying electricity is executed as soon as applying the first welding pressure, successively, applying electricity is continued with applying the second welding pressure stronger than that of the first. For example, to keep pressure and time constant and to change electric current, but the welding pressure is 1200kgf for the first welding pressure and 1800kgf for the second squeezing pressure, the time is a welding of 5 cycles and post heating of 8 cycles. By this method, defects of blow hole, undeposited part, etc., remained by the first pressure are vanished by pressing to conduct electricity, eliminating defected parts, a sound nugget is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance spot welding method for an Al-Li alloy used as a structural material for transportation vehicles such as railroad cars and automobiles, and particularly to Al-Li having few defects such as pores and unwelded parts. A method for resistance spot welding of alloys.

[0002]

2. Description of the Related Art As a method of joining structural materials such as railway cars and automobiles, resistance spot welding, which enables high efficiency, low cost and low strain joining, has been attracting attention. In addition, as a structural material for these transport aircraft, A with low density, high specific strength and high specific rigidity
Attempts have been made to apply 1-Li alloys.

Since Al--Li alloys are generally easy to perform resistance spot welding, resistance spot welding is simply performed in a single step of pressurizing and energizing, except for the case of thick materials. ing.

[0004]

However, unlike the general Al alloy, the Al-Li alloy has a drawback that defects such as pores and unwelded portions due to hydrogen gas may occur. When Al-Li alloys are applied to structural materials of railway vehicles and automobiles and resistance spot welding is used for joining the Al-Li alloys, Al-Li alloys or Al-Li alloys are used.
After resistance spot welding of Li alloy and other Al alloys, sound and good Al-L with few defects such as pores and unwelded parts
It is necessary to obtain a resistance spot welding nugget of i alloy material.

The present invention has been made in view of the above problems, and Al-containing few defects such as pores and unwelded portions.
An object of the present invention is to provide a method for resistance spot welding of a Li alloy.

[0006]

Al-Li according to the present invention
The resistance spot welding method for alloys is based on the Al-Li to be welded.
It is characterized by comprising a step of pressurizing the alloy material with a first pressurizing force and energizing, and a step of pressurizing the Al-Li alloy material with a second pressurizing force larger than the first pressurizing force and energizing it. And

[0007]

Since the Al-Li alloy needs to have low density, high specific strength and high specific rigidity, the Al-Li alloy is
Usually, a plate material or an extruded material is used. Such a high-strength and high-rigidity Al alloy contains 1% or more of Li. From the phase diagram, the maximum content of solid solution Li is about 4%, so in the present invention, an Al-Li alloy having a Li content of 1 to 4% is used. Moreover, Cu, Mg, Zr, Mn, Cr, Zn, V or T is added to this Al-Li alloy.
An element such as i may be appropriately added as an alloy element.

In the present invention, Al--
Li alloy materials are joined. That is, for resistance spot welding, in the first pressing step, the first pressing force is applied and the current is applied. Then, subsequently to that, the second pressurizing force larger than the first pressurizing force is applied to energize. In this second-stage pressurizing step, the welded portion is melted and pressure-bonded by applying electricity while applying a strong pressing force, and the defects and the like left by the first-stage pressurization are eliminated. Therefore, in the present invention, it is possible to obtain a sound nugget having no defects such as pores and unwelded portions.

However, the joint surface before resistance spot welding is
It is desirable to remove oxides and hydroxides on the surface by a mechanical method such as wire brushing or a method such as chemical cleaning to bring the surface to a certain clean state.

[0010]

EXAMPLES Next, the characteristics of the structures joined by the method of the present invention will be described in comparison with those joined by the conventional method.

An Al-Li (2.5% by weight) -Mg (2.0% by weight) alloy JIS tempered T6 treated plate material (thickness: 4 mm and 2.5 mm) is prepared. Wire brushed. Then, welding was carried out by a three-phase rectification welding machine by two kinds of welding methods: (1) conventional method and (2) two-stage pressing method of the present invention. (1) Conventional method The current was changed while the pressure and time were kept constant. The current and pressurization pattern are shown in FIG. However, applied pressure: 1200 kgf Time: 8 cycles In addition, the electrodes are Cr-
It is a Cu alloy and has a substantially cylindrical shape with a diameter of 20 mm, and its peripheral surface has a rounded shape curved in an arc with a radius of 150 mm in the electrode height direction. (2) Similarly to the two-stage pressurizing method of the present embodiment, the pressurization and the time were kept constant and the current was changed. The current and pressure pattern are shown in FIG. However, applied pressure: welding pressure 1200 kgf + forging pressure 1800 kgf Time: welding 5 cycles + post heat 8 cycles Note that the electrodes are all Cr-Cu alloys, and the upper electrode has a diameter of 20 mm and the radius of curvature of the peripheral surface is 150 mm. It has a roundness, the lower electrode has a diameter of 20 mm, and the peripheral surface is a flat one that is not curved in the height direction.

Table 1 below shows the diameter and strength of the nugget obtained under the resistance spot welding conditions, the presence or absence of the occurrence of medium dust, and the cross-sectional structure of the nugget. In this table 1,
As for the cross-section micro photo number, photo number 1 is shown in FIG.
4 corresponds to FIG. 4, photograph number 3 corresponds to FIG. 5, and photograph number 4 corresponds to the cross-sectional structure shown in FIG. 6, respectively. 3 to 6 are traces of the cross-sectional microstructure of the nugget.

[0013]

[Table 1]

Further, as shown in photographs 3 and 4 (FIGS. 5 and 6), the method of the present embodiment using the two-stage pressurization has fewer defects such as pores and unwelded portions than the conventional method, and is extremely small. A good nugget having a fine structure was obtained. As described above, according to the present invention, a good nugget having almost no defects can be obtained.

[0015]

As described above, according to the method of the present invention, a structure of an Al-Li alloy material having a sound nugget with few defects such as pores and unwelded portions can be obtained by resistance spot welding. .

[Brief description of drawings]

FIG. 1 is a diagram showing a welding pressure pattern according to an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional welding pressure pattern.

FIG. 3 is a trace drawing of a cross-sectional microstructure photograph of Conventional Example 1.

FIG. 4 is a trace drawing of a cross-sectional microstructure photograph of Conventional Example 2.

5 is a trace drawing of a cross-sectional microstructure photograph of Example 1. FIG.

6 is a trace drawing of a cross-sectional microstructure photograph of Example 2. FIG.

Claims (1)

[Claims] 1. A step of pressurizing an Al-Li alloy material to be welded with a first pressurizing force to conduct electricity, and applying the Al-Li alloy material with a second pressurizing force larger than the first pressurizing force. Press
A resistance spot welding method for an Al-Li alloy, which comprises a step of energizing.