CN115302061A

CN115302061A - Method for resistance spot welding of steel-aluminum dissimilar metal

Info

Publication number: CN115302061A
Application number: CN202211031019.3A
Authority: CN
Inventors: 杨上陆; 王艳俊; 刘仁东; 徐鑫; 吕冬; 芦延鹏
Original assignee: Angang Steel Co Ltd; Shanghai Institute of Optics and Fine Mechanics of CAS
Current assignee: Angang Steel Co Ltd; Shanghai Institute of Optics and Fine Mechanics of CAS
Priority date: 2022-08-26
Filing date: 2022-08-26
Publication date: 2022-11-08

Abstract

The invention provides a method for resistance spot welding of steel and aluminum dissimilar metals, aiming at the problems of resistance spot welding of steel workpieces and aluminum workpieces. Pass through a plurality of welding electrode in the aluminium work piece side, and only keep a welding electrode in the steel side and carry out resistance spot welding, because aluminium side stream current is more dispersed and steel side current is concentrated in whole current return, make the heat that the steel side receives more, and then can conduct to the aluminium work piece side fast, reduce because steel aluminium work piece melting point, the aluminium side temperature that resistivity and heat conductivity difference caused excessively concentrates the messenger and splashes, the problem that gas pocket and too thick intermetallic compound produced, temperature distribution when helping to regulate and control steel aluminium spot welding, reduce welding defects, promote the problem of joint performance and aluminum plate side surface adhesion.

Description

Method for resistance spot welding of steel-aluminum dissimilar metal

Technical Field

The present invention relates to the field of resistance spot welding, and more particularly to a method of resistance spot welding of dissimilar material stacks of a steel workpiece and an aluminum workpiece.

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 electrical resistivity, thermal conductivity, thermal expansion coefficient, and the like, because of the difference in melting point between aluminum and steel (the melting point of steel is 1300 ℃ or higher, the melting point of aluminum is only 660 ℃, and the melting point of aluminum is lower, and the strength difference is also large). The aluminum alloy has a low melting point, the aluminum alloy is melted by heat generated at a joint surface, the steel is not melted yet, and when the current stops, the cooling speed of the aluminum is high, the cooling speed of the steel is low, the difference of solidification shrinkage rates at an interface is large, so that 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 grow a Fe — Al layer of the resulting brittle metal part compound, while more and thicker brittle metal part compound 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. Meanwhile, due to the fact that an oxide film exists on the surface of the aluminum workpiece, steel and aluminum are difficult to wet, air holes and other defects are easily formed in the joint, and the joint performance is low.

CN106736000A discloses a method for resistance spot welding of aluminum steel dissimilar materials, which improves heat distribution of a steel-aluminum interface by using an electrode with a small end face on a steel side and a spherical electrode with a convex ring on an aluminum side, and further improves performance of a welding spot; the method needs to use welding electrodes with specific proportion sizes on both sides of the steel and the aluminum, has high requirements on the shape and the size of the welding electrodes, and is difficult to ensure stable welding quality.

CN110280880A discloses a method for improving the performance of a joint by adding a copper material on a contact interface of 6-series aluminum alloy and steel; the method needs to add extra materials, has higher cost, needs to accurately control a plurality of welding parameters, and has small range of materials and difficult guarantee of stability; and heat is generated in a large amount on the aluminum side, which also reduces the service life of the aluminum-side electrode.

CN110270750A discloses a method for resistance spot welding of an aluminum workpiece and a steel workpiece, which improves the heat production efficiency of a steel side material by adding a steel workpiece on the surface of the steel side in advance; although the method can improve the performance of the aluminum steel joint to a certain extent, the aluminum steel joint is always electrified on two sides in the spot welding process, most of heat is still conducted through the steel side, and therefore the utilization rate of heat efficiency is low.

Therefore, the resistance spot welding method which can improve the performance of the steel-aluminum spot welding joint conveniently, with low cost and high efficiency is lacked in the field.

Disclosure of Invention

Aiming at the problems, the invention provides a method for inhibiting a plurality of resistance spot welding defects of a steel-aluminum workpiece and improving the performance of a joint.

In order to solve the above problems, the present invention adopts a technical solution that:

a method for resistance spot welding of steel and aluminum dissimilar metals is characterized by comprising the following steps:

stacking a steel workpiece to be welded and an aluminum workpiece to form a stacked structure,

respectively placing a pair of welding electrode pairs with opposite polarities on the upper surface and the lower surface of the stacked structure;

placing at least 1 welding electrode with the same polarity as the surface electrode on any surface of the stacked structure in parallel, so that the current flowing through the aluminum workpiece is dispersed, and the current flowing through the steel workpiece is concentrated;

and the aluminum workpiece current flowing area is melted to form an intermetallic compound with the steel workpiece, and a steel-aluminum heterogeneous workpiece joint is formed after cooling and solidification.

Preferably, the welding current passes through the welding electrode during the energizing.

Preferably, the welding current forms a more gradual lower temperature field on the aluminum workpiece side and a higher temperature field distribution on the steel workpiece side.

Preferably, the parallel welding electrodes have a distance of not less than 2 mm.

Preferably, any of the parallel welding electrodes and the welding electrode of the welding electrode pair with opposite polarity can form a current loop, and each current loop can be controlled independently.

In a preferred example, in the welding process, the welding current loop current at two sides of the steel workpiece flows for a period of time, then the aluminum workpiece side electrode and the first surface side electrode of the steel workpiece are connected to form a loop, and the welding current is applied for a period of time.

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: pass through a plurality of welding electrodes in the aluminium work piece side, and only keep a welding electrode in the steel side and carry out resistance spot welding, because aluminium side flow current is more dispersed and steel side current is concentrated in whole current return circuit, make the heat that the steel side receives more, and then can conduct to the aluminium work piece side fast, can reduce because steel aluminium work piece melting point, aluminium side temperature that resistivity and heat conductivity difference caused excessively concentrates the messenger and splashes, the problem that gas pocket and too thick intermetallic compound produced, temperature field distribution when helping to regulate and control steel aluminium spot welding, reduce welding defects, promote the problem of joint performance and aluminum plate side surface adhesion.

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 the welding process of the present invention.

Fig. 2 is a schematic view of a combination of a first welding electrode and a second welding electrode.

Fig. 3 is a schematic view of the combination of a first bonding electrode and a second bonding electrode with an insert therebetween.

Fig. 4 is a top view of the structure shown in fig. 3.

Fig. 5 is a schematic view of the welding surface of the first welding electrode.

Reference numeral, 1-a first welding electrode; 2-a second welding electrode; 3-an aluminum workpiece; 4-a steel workpiece; 5-a third welding electrode; 11-current line; 12-aluminum nuggets; 13-an intermetallic layer; 11-a first welding electrode welding surface; 21-a second welding electrode welding surface; 31-an aluminum workpiece first surface; 32-an aluminum workpiece second surface; 41-a steel workpiece first surface; 42-a steel workpiece second surface; 51-a third welding electrode surface; d 1-the diameter of the outer circumference of the welding surface of the first welding electrode; d 2-the diameter of the outer circumference of the second welding electrode surface; d 3-the outside diameter of the welding surface of the third welding electrode; b-the distance between the first welding electrode and the second welding electrode.

Detailed Description

The inventor of the invention has found that the problems of more welding defects and low welding strength of resistance spot welding of steel and aluminum heterogeneous workpieces under normal conditions can be well avoided by prefabricating a convex structure on the side of the steel workpiece and then performing resistance spot welding of the heterogeneous metals, the joint strength is greatly improved, and a better welding spot is obtained, and the invention is completed on the basis.

The process of welding the dissimilar material comprises the following steps: stacking a steel workpiece to be welded and an aluminum workpiece to form a stacked structure,

a pair of welding electrode pairs with opposite polarities are respectively arranged on the upper surface and the lower surface of the stacked structure;

Term(s) for

As used herein, the term "opposing" means that for both surfaces of the stacked assembly, the "workpiece" broadly refers in the specification to a sheet metal layer, casting, extrusion, or any other structural member capable of resistance spot welding. The term "about" means within a tolerance in a manufacturing process that is generally acceptable in the art. The terms "upper", "lower", "outside", "inside", and the like are only used for relatively explaining the relative positional relationship, and there is no particular limitation in inside and outside.

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.

FIG. 1 shows a schematic diagram of a process using the present invention. The method for welding the aluminum workpiece 3 and the steel workpiece 4 comprises the following steps:

(1) Providing a steel workpiece 4 and an aluminum workpiece 3; the steel workpiece has a generally outwardly facing first surface 41 and a second surface 42; the aluminum workpiece also has generally outwardly facing first and

second surfaces

31 and 32;

(2) Stacking the steel workpiece and the aluminum workpiece to form a stacked structure; wherein the steel workpiece second surface 42 is in contact with the aluminum workpiece second surface 32, as shown in FIG. 1 (a);

(3) Providing a pair of welding electrodes for resistance spot welding, wherein one side of each welding electrode is provided with at least 2

independent welding electrodes

1 and 2, the other side of each welding electrode is provided with 1 third welding electrode 5, the welding electrodes on the same side are in parallel connection, and the parallel electrodes on the same side point to the first surface 31 of the aluminum workpiece; the other side welding electrode 5 is directed to the steel workpiece first surface 41 as shown in fig. 1 (b). And (3) applying current and pressure between the electrodes, so that the aluminum side material in the current applying area of the stacking part is melted and forms intermetallic compounds with the steel workpiece, and the steel-aluminum heterogeneous workpiece joint is formed after cooling and solidification.

Wherein resistance welding is performed by first moving the

welding electrode

1,2 as a whole and the welding electrode 5 to provide a welding pressure F to the stack combination, as shown in fig. 1 (b), typically F is 1000-12000N, preferably 2000-5000N; the welding contact surfaces 11, 21 of the welding electrodes are brought into precise contact with the first surface 31 of the aluminium workpiece, respectively. Then, one or more sections of welding current 11 are applied to flow through the

welding electrodes

1 and 2, and the aluminum workpiece is heated and melted to form an aluminum nugget 12, as shown in fig. 1 (c); during this process the welding pressure is maintained continuously, while the welding current may be one or more segments, either direct or alternating, which may be determined according to the particular workpiece fit-up combination; finally, after removing the welding electrode and the support member, an aluminum nugget 12 is formed on the aluminum workpiece side and the molten aluminum wets an intermetallic compound layer 13 formed after spreading the steel workpiece, forming an aluminum-steel heterogeneous workpiece spot weld joint, as shown in fig. 1 (d). Wherein the welding electrode 1 and the welding electrode 2 are connected in parallel and are connected to one end of a welding power supply, and the welding electrode 5 is connected to the other end of the welding power supply. It should be noted that the

welding electrodes

1,2 are shown in the drawings as being negative when the welding power is on and the welding electrode 5 is positive, but in practice both are more easily replaceable or are otherwise non-positive (as in the case of an ac power source) and the description is provided herein.

The paired

welding electrodes

1,2 are positioned on the aluminum side of the stacked assembly, and when any one of the welding electrodes is electrified with welding current, current loops can be formed between the welding electrode 1 and the welding electrode 5 and between the welding electrode 2 and the welding electrode 5, so that the current density on the aluminum side can be greatly reduced, the current density on the steel side can be improved, and the steel is heated quickly to transfer heat to the aluminum workpiece side to form a liquid molten pool.

The

welding electrodes

1,2, 5 each have a welding surface 11, 21, 51; the weld faces each have a circumferential diameter d1, d2, and d3. As shown in fig. 2, which is a schematic view of the welding surface of the welding electrode 1, the welding surface is a circular arc surface or plane, generally the radius of curvature r1 of the circular arc is more than 20mm, and d1 is 3-20mm, preferably 5-12mm; the end face diameter of the welding electrode 5 is generally larger than the end face diameters of the

welding electrodes

1 and 2; the

welding electrodes

1,2 have a spacing of not less than 2mm, preferably 3-5mm; the

welding electrodes

2 and 5 are also welding surfaces with circular arc profiles, the dimensional structure of which can be referred to the shape and size of the welding electrode 1 shown in fig. 2, it is noted that the three welding electrodes can be identical or different in dimensional profile, which can be selected according to the kind of the welded material; the welding surface is preferably a circular arc surface with a radius of curvature, typically not less than 40mm, in particular not less than 50mm on the contact surface on the aluminum side.

In practice, the welding current may flow in a variety of ways, as shown in FIG. 3 where the welding surface of the welding electrode 2 contacts the second surface 42 of the steel workpiece, the welding surface of the welding electrode 1 contacts the first surface of the aluminum workpiece, and the welding surface of the welding electrode 5 contacts the first welding surface of the steel workpiece. In this case, the welding electrode 1 and the welding electrode 5 may form a current loop 111, and the welding electrode 2 and the welding electrode 5 may also form a current loop 112; the two current loops can be independently controlled in a time-sharing mode, generally, the loop 112 is firstly connected to heat the steel workpiece 4, the temperature of the steel side rises and is transmitted to the aluminum side after the temperature of the steel workpiece rises for a period of time, then the current loop 111 is connected to accelerate the temperature rising speed of the aluminum side material, and meanwhile, the problem that the temperature of the aluminum side rises too fast during common resistance spot welding, so that the electrode adhesion is caused and the service life of the electrode is reduced due to too high temperature of the contact area of the electrode and the aluminum workpiece can be avoided. The electrifying heating mode can ensure that most of the heated aluminum side workpiece is transmitted from the steel side, the temperature field is uniform, and the phenomenon that the content is shrunk and cracks are caused due to too much aluminum melting amount is avoided. The time interval between two welding loops is greater than or equal to zero, which can be selected according to the combination and matching of the actual welding materials.

The contact center of the welding electrode 1 and the welding electrode 2 has a distance B of 3-15mm; preferably 4-12mm; the

welding electrodes

1,2 and 5 may be made of any electrically and thermally conductive material, such as copper alloys, including copper chromium (CuCr) alloys, copper chromium zirconium (CuCrZr) alloys, copper alloys with added aluminum oxide particles, or various other copper alloys that may be used as electrode materials;

in addition, another embodiment for realizing free heat distribution of the aluminum side steel side is shown in FIG. 4; when the welding electrode 2 cannot directly contact the second welding surface of the steel workpiece in some occasions, the hole 7 can be arranged on the side of the aluminum workpiece to accommodate the second welding electrode to pass through so that the welding surface of the second welding electrode can contact the second welding surface of the steel workpiece; the specific hole location and size can be determined by the size of the welding electrode shape and the material combination to be welded, in one embodiment the electrode outer diameter is 16mm, so the hole diameter is not less than 16mm, typically not less than 1.2 times, e.g. 20mm.

Referring now to FIG. 5, another type of embodiment is also possible in the present invention. When performing resistance spot welding, the steel workpiece 4 is first subjected to resistance spot welding heating at a position a by a pair of

welding electrodes

2, 5, as shown in fig. 5 (a); stacking the steel workpiece 4 and the aluminum workpiece 3 after a period of time, and immediately performing resistance spot welding in a second process, wherein resistance spot welding is performed at a position B by using the electrode pair 3 and the electrode pair 5 in the process, the position B and the position a have a distance B1 in the horizontal direction, the position a is a heating center position in the first process, and the position B is a heating center in the second process; generally, B1 is 0-20mm, preferably 5-16mm, and the specific size can be determined according to the size of the welding surface of the welding electrode, heating current, time and other parameters. The

welding electrodes

1,2, 5 performing resistance welding can have different end face topography structures in each process; the welding current in each welding process may also have multiple segments, and the welding devices performing each process may be the same or different devices, which are not described herein again.

As noted above, the welding current to perform resistance spot welding may be from any dc, ac welding controller, which may be constant current, constant voltage, constant power, or any form of constant phase angle during the welding process, as will be appreciated in the art. The heating and cooling process, which may be performed in one or more stages during resistance spot welding, in particular a plurality of pulses of welding current, each having a current output of the same or different magnitude, duration and interval, typically a total effective output current value of typically 5-40KA, preferably 10-35KA, and a current duration of 50-500ms, preferably 60-400ms, and the welding current in each process may be varied.

It should be noted that the stack shown in the schematic diagram of this embodiment is a structure in which single-layer workpieces are stacked on top of each other, but actually the present invention also includes a stacked combination of multiple-layer workpieces, and the thicknesses of the workpieces may be the same or different. Wherein the steel workpiece 4 may be: for example, one of cold rolled or hot rolled steel sheets such as quench-distributed steel (Q & P steel), dual phase steel (DP steel), transformation induced plasticity (TRIP steel), complex phase steel (CP steel), twinning induced plasticity (TWIP steel) and hot formed steel (PHS steel) may be of the same type or of different types, and is not limited strictly. And the material state thereof may include various tempering including heat treatment states such as annealing, strain strengthening, and the like. The thickness is 0.4-4mm, preferably between 0.5-3mm, more narrowly 0.8-2.0mm. The surface of the steel sheet may have a plating layer, and the kind of the plating layer may include Zn system, zn-Fe system, zn-Ni system, zn-Al system, zn-Mg system, etc. Examples of the high-strength steel sheet having a Zn-based plating layer include an alloyed hot-dip galvanized steel sheet, a hot-dip galvanized steel sheet, and an electrogalvanized steel sheet. The plating solution also comprises a precoating layer which is an aluminum alloy or an aluminum base and comprises the following components in parts by weight: 6-12% silicon, 1-5% iron, with the remainder being aluminium or inevitable impurities. The weight per unit area of the plating layer is not particularly limited, and the thickness of the plating layer is 3 to 40 μm. An inorganic or organic oil film (e.g., a lubricating oil film) may be formed on the surface of the plating layer. The aluminum workpiece 3 may be: such as aluminum alloys like aluminum magnesium alloys, aluminum silicon alloys, aluminum magnesium silicon alloys or aluminum copper alloys, or magnesium alloys like magnesium aluminum alloys, magnesium manganese alloys, magnesium zinc zirconium alloys, the thickness of the work piece is 0.5-3mm, preferably 0.8-2.5mm. Generally, an adhesive and a sealant widely used for resistance spot welding may be included between the steel workpiece 4 and the aluminum workpiece 3. The steel workpiece 4 and the aluminum workpiece 3 may be gapped or gapless.

Although the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. Therefore, the protection scope of the present invention is subject to the scope defined by the appended claims.

Claims

1. A method of resistance spot welding dissimilar metals to steel and aluminum, comprising the steps of:

2. A method of resistance spot welding a steel-aluminum dissimilar metal according to claim 1, characterized in that: the welding current passes through the welding electrode in the electrifying process.

3. A method of resistance spot welding a steel-aluminum dissimilar metal according to claim 1, characterized in that: the welding current forms a more gradual and lower temperature field on the aluminum workpiece side and a higher temperature field distribution on the steel workpiece side.

4. A method of resistance spot welding a steel-aluminum dissimilar metal according to claim 1, characterized in that: the distance between the welding electrodes in parallel connection is not less than 2 mm.

5. A method of resistance spot welding a steel-aluminum dissimilar metal according to claim 1 or 4, characterized in that: any welding electrode in parallel connection and the welding electrode with opposite polarity in the welding electrode pair can form a current loop, and each current loop can be independently controlled.

6. A method of resistance spot welding a steel-aluminum dissimilar metal according to claim 1, characterized in that: and the welding current output is kept constant in the welding process.

7. A method of resistance spot welding a steel-aluminum dissimilar metal according to any one of claims 1 to 6, characterized in that: in the welding process, the welding current loop current at the two sides of the steel workpiece flows for a period of time, then the aluminum workpiece side electrode and the first surface side electrode of the steel workpiece are connected to form a loop, and the welding current is applied for a period of time.