JPH067957A - Resistance spot-welding method for aluminum alloy - Google Patents

Abstract

PURPOSE:To improve the joining strength and the service life of an electrode at the time of spot-welding the aluminum alloy. CONSTITUTION:In the case of simultaneously executing both of the welding by arranging a high melting point aluminum alloy 2 at the positive electrode 1 side and a low melting point aluminum alloy 4 at the negative electrode 3 side and the welding by using the electrodes provided with the tip shape formed so that the impression diameter of the positive electrode 1 side is smaller than that of the negative electrode 3 side, the joining strength and the service life of the electrode are drastically improved at the time of spot-welding mutually the aluminum alloys having different melting point.

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 aluminum alloys (hereinafter, including aluminum), and more particularly to a resistance spot welding method for aluminum alloys suitable for improving joint strength and electrode life.

[0002]

2. Description of the Related Art Conventionally, aluminum alloys have been widely used, for example, for aluminizing automobiles, aircrafts, ships, various vehicles, etc., but when joining the aluminum alloys, resistance spot welding is compared. It is used extensively.

As a resistance spot welding technique for the aluminum alloy, for example, Japanese Patent Application Laid-Open No. 57-56175 is provided. In the resistance spot welding method described in the publication, a welded material is welded between an electrode and a material to be welded. Welding is performed by interposing a metal material (metal) having a lower thermal conductivity and a lower electrical conductivity than the material and a high melting point temperature.

[0004]

By the way, when different aluminum alloys are resistance spot-welded to each other when the melting points of the two aluminum alloys are different from each other, the nugget (welding region by resistance spot welding) is formed on the side of the aluminum alloy having the lower melting point. Has the property of growing large. For this reason,
Since the nugget is asymmetric with respect to the joint surface of both aluminum alloys, that is, one-side melting phenomenon occurs, the diameter of the joint surface of both aluminum alloys becomes smaller than the diameter of the nugget, resulting in sufficient joint strength. It has the drawback of not having it. In addition, since the life of the electrode of the welding machine applied to the side of the aluminum alloy with a low melting point is shortened, the number of continuous welding points of the electrode during welding is reduced, making it suitable for mass production in which dissimilar aluminum alloys are continuously processed by resistance spot welding. Has the drawback of not being suitable.

[0005]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems.
It is an object of the present invention to provide a resistance spot welding method for an aluminum alloy that achieves improvement in bonding strength and electrode life by utilizing the polarity of the electrode and changing the shape of the electrode.

[0006]

In order to achieve the above object, the present invention according to claim 1 is a resistance spot welding method of aluminum alloys in which aluminum alloys having different melting points are joined to each other. It is characterized in that an aluminum alloy having a high melting point is arranged and an aluminum alloy having a low melting point is arranged on the negative electrode side to perform resistance spot welding. According to a second aspect of the present invention, in an aluminum alloy resistance spot welding method for joining aluminum alloys having different melting points, an electrode having a tip shape such that the positive electrode side has a smaller indentation diameter than the negative electrode side. Is used to perform resistance spot welding. According to a third aspect of the present invention, in a resistance spot welding method for aluminum alloys, which is configured to join aluminum alloys having different melting points, an aluminum alloy having a high melting point is disposed on the positive electrode side and an aluminum alloy having a low melting point is disposed on the negative electrode side. It is characterized in that the resistance spot welding is performed by arranging an alloy and using an electrode having a tip shape such that the positive electrode side has a smaller indentation diameter than the negative electrode side.

[0007]

According to the resistance spot welding method for aluminum alloys of the present invention, the nugget that has grown to the side of the aluminum alloy having a low melting point is formed symmetrically with respect to the joint surface of both aluminum alloys, that is, It is possible to bring the joint surface near the center of the nugget having a substantially elliptical cross section. Thereby, the joint area of both aluminum alloys can be enlarged. Moreover, since the nugget is formed in a state of being separated from the electrode, the life of the electrode can be extended. Therefore, when resistance spot welding of different aluminum alloys having different melting points is performed, it is possible to improve the joint strength and electrode life of both aluminum alloys.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment to which the aluminum alloy resistance spot welding method of the present invention is applied will be described below with reference to the drawings.

First, before describing the resistance spot welding method for dissimilar aluminum alloys according to the present embodiment, a background art welding machine will be described. The resistance spot welding machine is roughly classified into an AC type and a DC type. , Generally AC type welding machine is the mainstream, but aluminum alloy has lower specific resistance and better thermal conductivity than mild steel,
Since it is preferable to apply a high welding current for a short time to perform welding rather than a low current for a long time, a DC welding machine such as a rectification type or an inverter type is used. ing.

When different types of aluminum alloys are welded together by using a copper alloy electrode of a DC welding machine, in the case of the DC type, there is an electrode polarity due to a thermoelectron effect such as Peltier effect or Thomson effect. However, there is a defect that the electrode life is shortened by shortening the electrode life. In this case, the Peltier effect is a phenomenon in which heat other than Joule heat based on electrical resistance is generated or absorbed at the junction point when current is applied to the junction point of dissimilar metals. When a current is flowed from copper to an aluminum alloy and from an aluminum alloy to copper when sandwiching and welding with a (positive electrode) and a copper alloy electrode (negative electrode), a difference in heat generation occurs at the contact points of both aluminum alloys. Therefore, in this embodiment, as will be described later, it is configured to have two characteristic points.

That is, the first characteristic point of the resistance spot welding method of the present embodiment is that when the two aluminum alloys having different melting points are joined together, the electrode polarity of the above-mentioned DC welding machine is utilized. 1, the aluminum alloy 2 having a high melting point is arranged on the positive electrode 1 side, and the aluminum alloy 4 having a low melting point is arranged on the negative electrode 3 side to perform spot welding (FIG. 1). Medium code 5 indicates a nugget). Thereby, when the welding current is applied, the positive electrode side generates more heat due to the action of the Peltier effect, and the penetration of the aluminum alloy having a high melting point can be increased, so that the joining strength of both aluminum alloys can be improved. There is. While the Peltier effect is proportional to the welding current, it has a large polarity when welding with a high welding current such as aluminum alloy,
It can be used for joining dissimilar aluminum alloys having different melting points.

Next, the second characteristic point of the resistance spot welding method of this embodiment is that by using an electrode having a tip shape in which the indentation diameter on the positive electrode side is smaller than that on the negative electrode side, the spot is formed. This is the point where welding is performed. As a result, the life of the electrode (the number of dots) can be improved. In this case, as the tip shape of the electrode, as shown in FIG. 2, for example, P type (point type), R type (spherical type or radius type), C type (cone trapezoidal type), E type (eccentric type), F type ( There are two types of shapes, a spherical shape and a flat shape.

By the way, the above-mentioned "small indentation diameter" means that the projected area (planar area) of the indentation generated when the tip of the electrode is pressed against the work with the same pressure. When the tip of the electrode having a small indentation diameter is spherical, the curvature diameter is small, and when the tip of the electrode having a small indentation diameter is planar, the area of the plane is small. Will be referred to as a pointed electrode.

Considering the influence of the tip shape of the electrode on the work based on the contact theory, assuming that the contact area between the electrode and the work is A, the pressing force of the electrode on the work is F, and the hardness of the work is H, Generally, the relational expression A = F / (ξH) is established between the contact area A, the pressing force F, and the hardness H. In this case, ξ is a value that takes into account surface conditions such as flatness and roughness in terms of pressure and surface factor.

In the case of resistance spot welding, approximately ξ = 1 between the electrode and the work, and when the hardness of the work is constant and the pressure applied to the electrode is constant, the contact area depends on the tip shape of the electrode. There is little effect, and the area in which the electrode is in contact with the workpiece hardly changes when the pressurizing pressure is the same whether the electrode with a sharp tip or the electrode with a rounded tip is used. . On the other hand, when an electrode with a sharp tip is used, compared to the case with an electrode with a rounded tip, the sharp electrode tip bites into the inside of the workpiece, so the projected contact area (planar) As a result, the current density of the electrode with a sharp tip becomes higher than that of the electrode with a round tip when energized. That is, since it is possible to generate heat in the positive electrode without diffusing the heat in the negative electrode, it is presumed that the amount of penetration becomes larger.

Next, according to the resistance spot welding method of this embodiment, an aluminum die casting alloy JIS H5202 is used.
(1982) 2 mmt plate of AC4C (hereinafter abbreviated as AC4C) (melting point about 590 degrees C) and aluminum alloy extruded material JIS H4100 (1988) A6061 (hereinafter abbreviated as A6061) (melting point about 650 degrees C) 2 mm
Experimental results of tensile shear strength and electrode life when resistance spot welding is performed on a t-plate will be described.

In the tensile shear strength and electrode life experiments of this example, a three-phase rectification type spot welder was used, welding current was 32000A, welding time was 5 cycles, and welding pressure was 800K.
Under welding conditions of gf, the tip shape is 150R and 100
When welding was performed using a combination of the electrode and the sample arrangement using the R electrode, the results of tensile shear strength and electrode life were as shown in FIG. In this case, in the tensile shear strength test, the average value was calculated by performing all the tests until the life of the electrode was reached, and when even a slight seizure of the electrode occurred, it was judged as the electrode life.

Experiment 1: The tip shape of the electrode was kept constant at 150 R, the placement material on the negative electrode side (welding sample) was a casting (aluminum die-cast alloy AC4C), and the placement material on the positive electrode side was a profile (aluminum alloy extruded material A606).
1), the tensile shear strength is 6500 (N / s)
The electrode life was as long as 150 dots.

Experiment 2: Tensile shear strength is 600 when the tip shape of the electrode is constant at 150R, the placement material on the negative electrode side is a profile, and the placement material on the positive electrode side is a casting.
It was as low as 0 (N / spot), and the electrode life was as short as 13 points.

Experiment 3: A casting material was used for the negative electrode side and a shape material was used for the positive electrode side. The tip shape on the negative electrode side was 150R and the tip shape on the positive electrode side was 100R.
, The tensile shear strength is 8100 (N / spo
t), which was even higher, and the life of the electrode was 2800 dots, which was longer.

Experiment 4: The placement material on the negative electrode side was a casting, the placement material on the positive electrode side was a shape, and the tip shape on the negative electrode side was 100R and the tip shape on the positive electrode side was 150R.
, The tensile shear strength is 6100 (N / spo
t) and the life of the electrode was as short as 5 points.

As described above, according to the resistance spot welding method of this embodiment, the aluminum alloy having a high melting point is arranged on the positive electrode side and the aluminum alloy having a low melting point is arranged on the negative electrode side, which is the first characteristic point. And the second characteristic point is that welding is performed by using an electrode having a tip shape such that the positive electrode side has a smaller indentation diameter than the negative electrode side. If both are performed at the same time, the two complement each other, so that a more remarkable effect can be achieved as compared with the case where both are performed independently.

That is, during resistance spot welding of different aluminum alloys, by utilizing the polarity of the electrodes and changing the shape of the electrodes, the nugget that has grown to the side of the aluminum alloy having a lower melting point is biased. It becomes possible to form symmetrically with respect to the joint surface, in other words, it becomes possible to bring the joint surface near the center of the substantially oval-shaped nugget in the sectional view, and to increase the joint area of both aluminum alloys. You can Further, since the nugget is formed apart from the electrode, the life of the electrode can be extended. Therefore, when resistance spot welding of different aluminum alloys having different melting points is performed, it becomes possible to greatly improve the bonding strength and the electrode life as compared with the conventional case.

[0024]

As described above, according to the present invention,
An aluminum alloy with a higher melting point is placed on the positive electrode side, an aluminum alloy with a lower melting point is placed on the negative electrode side, and the tip shape is such that the indentation diameter on the positive electrode side is smaller than that on the negative electrode side. Since using the electrode provided with, it is possible to symmetrically form a nugget that has grown while being deviated to the aluminum alloy side having a low melting point, with respect to the joint surface of both aluminum alloys, in other words,
It is possible to bring the joint surface near the center of the substantially elliptical nugget, and as a result, it is possible to increase the joint area of both aluminum alloys. Moreover, since the nugget portion is separated from the electrode, the life of the electrode can be extended. As a result, it is possible to significantly improve the bonding strength and the electrode life when resistance spot welding different aluminum alloys having different melting points, which has been conventionally considered difficult.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an arrangement of electrodes and a workpiece in resistance spot welding according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a tip shape of an electrode.

FIG. 3 is a diagram showing experimental results of tensile shear strength and electrode life of a welding material.

[Explanation of symbols]

 1 Positive electrode 2 Aluminum alloy 3 Negative electrode 4 Aluminum alloy 5 Nugget

Claims (3)

[Claims] 1. A resistance spot welding method for aluminum alloys, wherein aluminum alloys having different melting points are joined together, wherein an aluminum alloy having a high melting point is arranged on the positive electrode side and an aluminum alloy having a low melting point is arranged on the negative electrode side. A resistance spot welding method for an aluminum alloy, characterized in that the resistance spot welding is performed. 2. A resistance spot welding method of aluminum alloys in which aluminum alloys having different melting points are joined to each other, wherein an electrode having a tip shape such that the positive electrode side has a smaller indentation diameter than the negative electrode side is used. Resistance spot welding method for aluminum alloys, characterized in that resistance spot welding is performed. 3. A resistance spot welding method of aluminum alloys in which aluminum alloys having different melting points are joined to each other, wherein an aluminum alloy having a high melting point is arranged on the positive electrode side and an aluminum alloy having a low melting point is arranged on the negative electrode side. In addition, the resistance spot welding method for an aluminum alloy is characterized in that the resistance spot welding is performed using an electrode having a tip shape such that the positive electrode side has a smaller indentation diameter than the negative electrode side.