Preparation of interface layer for dissimilar metal connection and welding method based on interface layer

Abstract

The present invention provides a preparation method of an interface layer for connecting dissimilar metals and a welding method based on the interface layer. The first step is to deposit a layer of AlNi intermetallic compound film with a thickness of nanometers on the surface of steel by a vapor deposition method, and the AlNi intermetallic compound has a simple cubic structure; the second step is to use the nanometer-scale AlNi intermetallic compound film deposited on the surface of the steel as the interface layer for connecting the magnesium alloy and the steel; the third step is to use an ultrasonic spot welding method to achieve the metallurgical connection of the magnesium alloy / steel with a pre-set AlNi intermetallic compound layer, and to obtain the interface connection structure of the magnesium alloy / AlNi intermetallic compound layer / steel by optimizing the welding process parameters. The present invention controls the type and thickness of the interface layer by pre-setting the interface layer, and at the same time promotes the metallurgical reaction between the interface layer and the alloy elements of the parent materials on both sides, and maintains the structural integrity of the interface layer. The method has the characteristics of adjustable type and thickness of the interface layer, is convenient for mass production, and can expand the scope of application.

Description

Technical Field

[0001] The invention relates to an interface layer preparation for dissimilar metal connection and a welding method based on the interface layer. Background Art

[0002] Under the background of global participation in energy conservation and emission reduction, lightweighting has gradually become an important development direction of the manufacturing industry. Improving the strength of the parent material and selecting lightweight materials are the main means to achieve lightweighting. With the in-depth application of high-strength structural materials and light metal materials in aerospace, automobile, 3C and other fields, the design and manufacturing technology of multi-material composite structures have made great progress in the above fields. Magnesium alloys have the characteristics of high specific strength, good shock absorption performance and low density. Steel, as the most widely used metal material, has the characteristics of high strength, good plasticity and toughness, and good corrosion resistance. However, the density of steel is relatively large, which increases energy consumption. On the basis of meeting the use of structural materials, a method of using magnesium alloy to replace part of the steel is proposed, and high-strength steel is selected to replace ordinary steel, which can not only reduce the weight of the components, but also meet the requirements of aerospace, automobile, 3C and other fields for lightweight and high performance of components, and has broad application prospects.

[0003] For magnesium alloys / steels, which are difficult to dissolve and react with each other, since there are no intermetallic compounds between Mg and Fe and the solid solubility between them is extremely low, promoting interface reaction is the key to achieving metallurgical connection of difficult to dissolve and react with each other. Existing studies have pointed out that when AZ series magnesium alloys are welded with steel, it is mainly the small amount of Al element in the magnesium alloy that reacts with the alloying elements in the steel to form an interface layer at the magnesium alloy / steel interface, thus achieving metallurgical connection of magnesium alloy / steel. However, during the welding process of magnesium alloy / steel, with the changes in welding methods, process parameters and added alloying elements, the type and thickness of the magnesium alloy / steel interface layer will change greatly, and the performance of magnesium alloy / steel joints is difficult to directly regulate. In view of the difficulty in welding dissimilar metal magnesium alloys / steels that are difficult to dissolve and react, the present invention proposes to pre-deposit an interface layer on the surface of the base material before welding the dissimilar metals, thereby ensuring the integrity of the interface layer structure during the welding process, and at the same time allowing the interface layer to react with the base materials on both sides to achieve metallurgical connection, thereby solving the problem of joint failure or poor performance caused by insufficient interface reaction of dissimilar metals that are difficult to dissolve and react. At the same time, high-quality welding of dissimilar metal magnesium alloys / steels that are difficult to dissolve and react can be achieved by regulating the type and thickness of the interface layer. Summary of the invention

[0004] The purpose of the present invention is to provide a solution to the problem of insufficient interface reaction of dissimilar metals that are difficult to dissolve and react, by promoting the metallurgical connection of dissimilar metals that are difficult to dissolve and react by adding a pre-set film (interface layer), and by achieving metallurgical welding of dissimilar metals that are difficult to dissolve and react while ensuring that the interface layer is not destroyed through a welding method.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: a method for preparing an interface layer when connecting magnesium alloy / steel dissimilar metals, and a welding method for connecting dissimilar metals.

[0006] The present invention is aimed at connecting dissimilar metals that are difficult to dissolve and do not react, mainly magnesium alloy / steel.

[0007] Method for preparing interface layer before connecting dissimilar metals that are difficult to dissolve and react: physical vapor deposition method.

[0008] The interface layer is a single-layer structure, and the thickness of the interface layer is nanometer level, and its thickness is between 50 and 1000 nm.

[0009] The preset interface layer can achieve complete coherence or semi-coherence with the single-sided parent material, and the mismatch between the close-packed surface or sub-close-packed surface of the film structure and the close-packed surface or sub-close-packed surface of the steel is less than 20%.

[0010] Dissimilar metal joining methods include ultrasonic welding, friction stir welding, friction welding, explosion welding, diffusion welding, and resistance spot welding, etc. It also includes other welding methods that can make the interface layer between two dissimilar materials and maintain the structural integrity of the interface layer.

[0011] The preset interface layer maintains the integrity of size and structure after welding, and the interface layer is metallurgically connected to both sides.

[0012] The purpose of the present invention is to provide a preparation method for the connection of dissimilar magnesium alloys and steels that are difficult to dissolve and react, by pre-setting an interface layer, controlling the type and thickness of the interface layer, and at the same time promoting the metallurgical reaction between the interface layer and the alloy elements of the parent materials on both sides, and maintaining the structural integrity of the interface layer. The preparation method is simple in process and has a wide range of applications, and is convenient for large-scale batch production of dissimilar metal connections that are difficult to dissolve and react.

[0013] Compared with the existing difficult to dissolve non-reactive dissimilar metal connection technology, the present invention has the following advantages: the type and thickness of the interface layer are controllable, and the interface layer is pre-set on the steel side parent material, and the interface layer is metallurgically connected with the parent materials on both sides by solid phase welding method to achieve dissimilar metal connection; the interface layer can be selected to be coherent or semi-coherent with the parent materials on both sides by design, so as to achieve the purpose of performance enhancement; the crystal structure and plastic toughness of the interface layer can be changed by designing the composition of the interface layer, so as to achieve the composition and structure design of the interface layer. The welding material of the present invention can meet the welding requirements of joint forms such as butt joints, lap joints and T-joints. DETAILED DESCRIPTION

[0014] In the following, the welding method of the dissimilar metal tailor-welded blanks based on the interface layer design is described in detail. In addition, the interface layer presetting method, the magnesium alloy / steel dissimilar metal connection method based on the presetting interface layer, and the type of base material selected for welding are not limited by the following specific implementation methods.

[0015] (1) The steps of the magnesium alloy / steel dissimilar metal joining method based on the design of nano-scale AlNi interface layer are as follows:

[0016] Firstly, the widely used AZ31B magnesium alloy sheet and the automotive DP800 high-strength steel sheet were selected as heterogeneous metal connection materials, both of which have a thickness of 1 mm.

[0017] Step 1: Preparation of AlNi alloy target

[0018] Using powder metallurgy technology, Al and Ni atoms are mixed in a 1:1 ratio to prepare an alloy target with a diameter of 75 mm and a thickness of 2 mm.

[0019] AlNi has a B2 structure with a lattice constant of a=b=c=2.887 Å. When Fe has a BCC structure, the lattice constant is a=b=c=2.860 Å. When Fe has a FCC structure, the lattice constant is a=b=c=2.649 Å. The close-packed plane of AlNi can achieve almost complete coherence with the close-packed planes of BCC and FCC structured Fe, respectively.

[0020] For Al-Ni compounds, A1Ni, A13Ni, A1Ni3 and A13Ni5 alloys are ductile materials, and the order of toughness is A1Ni>AlNi3>A13Ni5>A13Ni, while A14Ni3 and A13Ni2 are brittle materials. In this example, AlNi compounds with better toughness are selected as the preset interface layer.

[0021] Step 2: Steel Plate Surface Treatment

[0022] The surface of the DP800 steel plate was ground with 2000# sandpaper and then polished to ensure the flatness of the surface of the DP800 steel plate; the surface of the DP800 high-strength steel plate was pickled with a 5% sulfuric acid aqueous solution and then wiped with 95% industrial alcohol to obtain a clean and completely exposed steel plate.

[0023] Step 3: Deposition of thin film on the steel plate surface

[0024] The AlNi alloy target was bombarded by magnetron sputtering, and the target atoms were sputtered and deposited on the DP800 high-strength steel substrate. The sputtering power was 60-150 W, the sputtering time was 0.5-30 h, and the thickness of the AlNi film was controlled at 50-1000 nm. The continuity of the interface layer was maintained.

[0025] Step 4: Surface treatment of magnesium alloy plate

[0026] The surface of the magnesium alloy plate was polished with 2000# sandpaper to remove the oxide scale and oil stains on the surface of the magnesium alloy plate, and then the surface of the magnesium alloy plate was wiped with 95% industrial alcohol to obtain a magnesium alloy plate with a clean surface and completely exposed.

[0027] Step 5: Magnesium alloy / steel dissimilar metal resistance spot welding

[0028] The DP800 high-strength steel plate with a pre-film was resistance spot welded with the AZ31 magnesium alloy plate. The welding current was 10~20 kA, the electrode pressure was 2~3.5 kN, the welding time was 10~15 cycles, the electrode cap was FB-25 type, the end face diameter was 6 mm, and the thickness of the AlNi film after welding was controlled at 50~1000 nm.

[0029] Example According to the selected compound type, the AlNi alloy target with the target composition is directly prepared. As a thin film on the steel surface, AlNi and α-Fe are completely coherent. By adjusting the process parameters in magnetron sputtering, AlNi films of different thicknesses are prepared. The film thickness is controlled at 50~1000 nm, and finally a DP800 steel sheet with a preset interface layer is obtained.

[0030] The DP800 steel with a preset interface layer and the AZ31B magnesium alloy sheet were overlapped by ultrasonic spot welding. The AZ31B magnesium alloy sheet was at the top, in direct contact with the welding head, and the DP800 steel sheet with a preset film was at the bottom, connected to the base. The DP800 steel / AZ31B magnesium alloy welded joint was heat treated in a heat treatment furnace, with a holding temperature of 300~420 °C and a holding time of 0.5~16 h. The joint strength was about 0.6 kN.

[0031] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A welding method based on the interface layer of dissimilar metal connection, characterized in that: The steps include: The first step is to prepare AlNi intermetallic compound target: Using powder metallurgy technology, Al and Ni atoms are mixed in a 1:1 ratio to prepare an AlNi intermetallic compound target with a diameter of 75 mm and a thickness of 2 mm; Step 2: Surface treatment of steel plate: The surface of the DP800 steel plate with a thickness of 1 mm was ground with sandpaper and then polished to ensure the smoothness and flatness of the steel plate surface; the surface of the steel plate was pickled with a sulfuric acid aqueous solution and then wiped with industrial alcohol to obtain a clean and completely exposed steel plate substrate; Step 3: Deposition of thin film on the steel plate surface: The target atoms in the AlNi intermetallic compound target prepared in the first step are sputtered out by magnetron sputtering bombardment technology and deposited on the steel substrate processed in the second step to form a prefabricated interface layer; the sputtering power is 60-150W, the sputtering time is 0.5-30h, the continuity of the interface layer is maintained, and the thickness of the AlNi film deposited on the steel substrate is controlled to be 50-1000nm; Step 4: Surface treatment of magnesium alloy plate: The surface of the AZ31B magnesium alloy plate with a thickness of 1 mm was polished with sandpaper to remove the oxide scale and oil stain on the surface of the magnesium alloy plate, and then the surface of the magnesium alloy plate was wiped with industrial alcohol to obtain a magnesium alloy plate with a clean surface and completely exposed; Step 5: Magnesium alloy / steel metal resistance spot welding: The magnesium alloy plate treated in the fourth step is overlapped on the steel plate on which the AlNi film prefabricated interface layer is deposited in the third step, and resistance spot welding is performed to make the prefabricated interface layer react with the magnesium alloy to achieve metallurgical connection between the DP800 steel plate and the AZ31B magnesium alloy plate; The resistance spot welding has a welding current of 10-20 kA, an electrode pressure of 2-3.5 kN, a welding time of 10-15 cycles, an electrode cap of FB-25 type, and an end face diameter of 6 mm; During welding, the steel plate is kept in full contact with the lower electrode, and the upper electrode is pressed from top to bottom against the magnesium alloy plate, with the joint located at the center of the overlap area with the magnesium alloy plate and the steel plate; Step 6: Heat treatment of welded joints: The DP800 steel / AZ31B magnesium alloy welded joint formed by five-step resistance spot welding is placed in a heat treatment furnace for heat treatment at a holding temperature of 300 to 420°C for a holding time of 0.5 to 16 hours, so that the strength of the welded joint reaches 0.6 kN.