阅读说明：本技术 一种电阻点焊异种金属的方法 (Method for resistance spot welding of dissimilar metals ) 是由 杨上陆 王艳俊 于 2018-08-16 设计创作，主要内容包括：一种电阻点焊异种金属的方法。本发明针对焊接熔点不同或强度不同的金属存在的问题,通过在高熔点工件表面设置凹陷结构,使得在进行电阻点焊时高熔点工件与低熔点工件接触面积不同,改变温度场与应力场的分布,使温度集中于低熔点工件与高熔点工件两侧,并驱使熔化的低熔点熔核向高熔点工件的凹陷处运动,从而减少熔点不同的金属焊接存在的气孔等缺陷。(A method for resistance spot welding dissimilar metals. Aiming at the problems of welding metals with different melting points or different strengths, the invention arranges a concave structure on the surface of a high-melting-point workpiece, so that the contact area of the high-melting-point workpiece and a low-melting-point workpiece is different when resistance spot welding is carried out, the distribution of a temperature field and a stress field is changed, the temperature is concentrated on the two sides of the low-melting-point workpiece and the high-melting-point workpiece, and a molten low-melting-point nugget is driven to move to the concave part of the high-melting-point workpiece, thereby reducing the defects of air holes and the like in the welding of.)

1. A method of resistance spot welding dissimilar metals, the method comprising the steps of:

(1) providing two workpieces with different melting points, wherein the surface of the workpiece with the high melting point is provided with a concave structure;

(2) stacking a low melting point workpiece together with the high melting point workpiece;

(3) one or more separate resistance spot welds are performed on the stacked workpieces with a first welding electrode and a second welding electrode, wherein the weld is located at a recessed location of the high melting point workpiece.

2. The method of claim 1, wherein: the high-melting-point workpiece and the low-melting-point workpiece are made of materials with melting point difference or strength difference, such as steel, aluminum alloy, magnesium or magnesium alloy.

3. The method of claim 1, wherein: the recessed structure is a blind hole or a through hole.

4. The method of claim 3, wherein: the through hole is cylindrical and has a diameter of 0.5mm-10 mm.

5. The method of claim 1, wherein: the thickness of the low-melting-point workpiece and the high-melting-point workpiece is 0.3mm-6.0 mm.

6. The method of claim 1, wherein: the depth range of the concave structure is 5% -100% of the thickness of the high-melting-point workpiece.

7. The method of claim 1, wherein: when the high melting point workpiece is stacked with the low melting point workpiece, the concave side may generally face the low melting point workpiece or the first welding electrode side.

8. The method of claim 1, wherein: the depressions may be formed by a single or multiple process such as a cold process such as a machining process, a melting process, a punching process, a thread process, or a hot process.

9. The method of claim 2, wherein: the steel workpiece is bare or coated metal, and the matrix metal is low-carbon steel, interstitial free steel, dual-phase steel, multi-phase steel, twin crystal induced steel, cold-formed steel or hot-formed steel.

10. The method of claim 2, wherein: the aluminum alloy workpiece is wrought aluminum alloy or cast aluminum alloy, and the magnesium alloy is wrought magnesium alloy or cast magnesium alloy.

Technical Field

The present invention relates to the field of resistance spot welding, and more particularly to resistance spot welding together workpieces having differences in melting point or strength.

Background

In recent years, the weight reduction of automobiles has become a trend of the development of automobiles in the world due to the demands for environmental protection and energy conservation, and light alloy materials such as aluminum alloys and magnesium alloys are favored by manufacturers of large automobiles because the density of the light alloy materials is far lower than that of steel materials, but the overall mechanical properties of the steel materials are better than those of the light alloy materials, so that the connection of the light alloy materials and the steel materials becomes a preferable scheme for the weight reduction of the automobiles, which involves the connection problem between the light alloy and the steel.

Resistance spot welding relies on the flow of electrical current through contacting metal workpieces and across the interface resistance between them to generate heat to melt weld the connections together. However, when welding dissimilar materials, particularly aluminum alloys and steels, it is very difficult to weld them together due to the difference in the melting points of aluminum and steel (the melting point of steel is 1300 ℃ or higher, the melting point of aluminum is only 660 ℃, the melting point of aluminum alloy is lower, and the strength difference is large), the difference in electrical resistivity, thermal conductivity, thermal expansion coefficient, and the like. The aluminum alloy has low melting point, the aluminum alloy is melted by heat generated at a joint surface, the steel is not melted, the cooling speed of the aluminum is high when the current stops, the steel is cooled slowly, the solidification shrinkage rate difference at an interface is large, obvious defects such as air holes, cracks and the like easily occur at the final joint, and reliable welding cannot be realized. Furthermore, the higher temperature generated at the interface joint due to the higher resistivity of the steel workpiece will cause Fe — Al layer growth of the resulting brittle metal part compound, while more and thicker brittle metal part compounds will severely reduce the strength of the welded joint. It is therefore important how to better control the heat balance between the aluminium and steel workpieces so that the molten metal can be melted and cooled to solidify in a desirably controlled manner.

Disclosure of Invention

The invention provides a method for arranging a concave structure on the surface of a high-melting-point workpiece to overcome the defects of resistance spot welding dissimilar metals.

In order to solve the above problems, the present invention adopts a technical solution that: a method of resistance spot welding dissimilar metals, the method comprising the steps of:

(1) providing two workpieces with different melting points, wherein the surface of the workpiece with the high melting point is provided with a concave structure;

(2) stacking a low-melting-point workpiece and a high-melting-point workpiece together;

(3) one or more separate resistance spot welds are performed on the stacked workpieces with a first welding electrode and a second welding electrode, wherein the weld is located at a recessed location on the high melting point workpiece.

In another preferred example, the high melting point workpiece is steel, and the high melting point workpiece and the low melting point workpiece are materials with a melting point difference or a strength difference, such as steel, aluminum alloy, magnesium or magnesium alloy.

In another preferred example, the recessed structure is a blind hole or a through hole.

In another preferred embodiment, the through hole is cylindrical and has a diameter of 0.5mm to 10 mm.

In another preferred embodiment, the thickness of the low melting point and high melting point workpieces is 0.3mm to 6.0mm, preferably 0.5mm to 3.0 mm.

In another preferred embodiment, the depth of the concave structure is in the range of 5% -100% of the thickness of the high melting point workpiece.

In another preferred example, the depressions may be formed by a single or multiple processes such as a cold process such as a machining process, a melting process, a punching process, a thread process, or a hot process.

In another preferred embodiment, the steel workpiece is bare or coated with a metal and the base metal is a low carbon steel, interstitial free steel, dual phase steel, multi-phase steel, twin induced steel, cold formed steel or hot formed steel.

In another preferred example, the aluminum alloy workpiece is a wrought aluminum alloy or a cast aluminum alloy, and the magnesium alloy is a wrought magnesium alloy or a cast magnesium alloy.

It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.

The invention has the beneficial effects that: the concave structure is arranged on the surface of the high-melting-point workpiece, so that the contact area of the high-melting-point workpiece and the low-melting-point workpiece is different when resistance spot welding is carried out, the distribution of a temperature field and a stress field is changed, the temperature is concentrated on two sides of the low-melting-point workpiece and the high-melting-point workpiece, the molten low-melting-point nugget is driven to move to the concave position of the high-melting-point workpiece, the defects such as air holes are reduced, a larger joint surface is formed, the joint interface is uniformly distributed and not along the direction of the lap joint surface, and the growth of brittle intermetallic compounds is favorably inhibited due to the more uniform distribution of the temperature field and the stress field, so that.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other alternative embodiments can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic view of resistance spot welding according to embodiment 1 of the present invention.

Fig. 2 is a sectional view of a concave structure of a steel workpiece when the concave structure is cylindrical.

Fig. 3 is a cross-sectional view when the cross-sectional shape of the recess structure is a screw thread.

FIG. 4 is a schematic diagram of the steel workpiece when the concave structure is a blind hole.

Fig. 5 is a schematic view of resistance spot welding according to embodiment 2 of the present invention.

FIG. 6 is a cross-sectional view of a solder joint obtained by the method of the present invention.

FIG. 7 is a cross-sectional view of a solder joint obtained without the method of the present invention.

Fig. 8 is an enlarged view at the position e in fig. 6.

Reference numeral, 1-steel workpiece; 2-a recessed structure; 3-an aluminum or aluminum alloy workpiece; 4-a first welding electrode; 5-a second welding electrode; 6-welding spot aluminum nuggets; 7-nugget internal defects; 8-welding a joint surface of aluminum and steel; 9-self-locking structure joint surface; h-depression depth; d-range of diameters for a cylindrical configuration of the recess.

Detailed Description

The inventor of the present invention has made extensive and intensive studies, and found through a large number of experiments that the method of resistance spot welding dissimilar metals after forming a recessed structure on a high-melting-point workpiece can well avoid the problems of many welding defects and low welding strength of resistance spot welding of the dissimilar metals under normal conditions, greatly improve the joint strength, and obtain a better welding spot, thereby completing the present invention.

The process of welding the dissimilar material comprises the following steps: when welding, firstly, the low-melting-point workpiece and the high-melting-point workpiece with the concave structure are lapped together in a certain mode, then a first welding electrode and a second welding electrode of the resistance spot welding machine are in contact with the two workpieces, and the resistance spot welding machine is started to weld the two workpieces together.

Term(s) for

As used herein, the term "recessed feature" refers to the creation of a blind or through hole in the surface of a workpiece that is lower than the original workpiece surface, and "workpiece" broadly refers in this specification to a sheet metal layer, casting, extrusion, or any other structural member capable of resistance spot welding. The term "about" means within tolerances in a manufacturing process that is generally acceptable in the art. The term "high melting point workpiece" refers to a high melting point or high strength workpiece, and the term "low melting point workpiece" refers to a low melting point or low strength workpiece, and since some dissimilar metals have similar melting points but different strengths (e.g., aluminum alloy and magnesium alloy), the same effect can be obtained by using the method of the present invention, the term "poor melting point" refers to "poor melting point" or "poor strength," the term "high melting point workpiece" refers to high melting point or high strength workpiece, and the term "low melting point workpiece" refers to low melting point or low strength workpiece, and thus, the description thereof is omitted.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, the drawings are schematic and, thus, the apparatus and devices of the present invention are not limited by the size or scale of the schematic.

It is to be noted that in the claims and the description of the present patent, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, the use of the verb "comprise a" to define an element does not exclude the presence of another, same element in a process, method, article, or apparatus that comprises the element.

Furthermore, the numerical ranges provided in this specification are intended to include the end limit values thereof, and further, while the invention is described as being used in the construction of vehicle body parts, the detailed methods and assemblies may be adapted for use in other fields as well, such as industrial equipment, aerospace, and the like.