A welding method for tailor-welded plates of dissimilar metals

Abstract

The invention discloses a welding method for dissimilar metal tailor-welded plates. A layer of pure Ni powder is sprayed on the steel plate in the thickness direction; the thickness of the pre-sprayed layer Ni is regulated by changing the spraying parameters, wherein the pure Ni powder sprayed on the side of the steel serves as a transition layer for connecting the magnesium alloy and the steel; an intelligent welding robot based on machine vision realizes high-precision operation of the motion trajectory, and its accuracy reaches 0.05 mm; a laser-arc composite melting welding method is used to realize the metallurgical connection of the magnesium alloy / steel with a pre-set pure Ni transition layer, and the melting amount of the steel side is regulated by controlling the offset of the laser on the steel side, so as to realize the high-quality connection of the magnesium alloy / steel. The transition layer preparation method for connecting magnesium alloy / steel tailor-welded plates of the present invention has the characteristics of adjustable transition layer type and thickness; the high-precision intelligent welding robot has the characteristics of controllable laser offset and high offset accuracy, so as to realize high-precision welding of welds.

Description

Technical Field

[0001] The invention relates to a magnesium alloy / steel tailor-welded plate welding transition layer preparation technology, an intelligent welding robot weld tracking technology, and fusion welding of difficult-to-solubilize and non-reactive dissimilar materials based on the transition layer preparation and weld tracking technology. Background Art

[0002] In the context of global energy conservation and emission reduction, lightweighting has gradually become an important development direction for 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, automobiles, 3C and other fields, the design and manufacturing technology of multi-material composite structures has made great progress in the above fields.

[0003] In the design of the body structure, the use of "tailor-welded plates" can achieve the purpose of reducing the weight of the car, and the tailor-welded plate structure design mainly adopts the butt-jointing method. With the rapid development and mass production of high-performance magnesium alloy sheets for automobile bodies, the manufacture of magnesium alloy / steel hybrid body structure tailor-welded plates has become one of the important ways to expand the application of magnesium alloys in car bodies.

[0004] For the connection of magnesium alloy / steel welded plates, which are difficult to dissolve and react, on the one hand, since Mg and Fe do not have any intermetallic compounds and their solubility is extremely low, alloying elements need to be added to promote the interface reaction; on the other hand, since magnesium alloy / steel welded plates belong to butt structures, insufficient interface reaction will produce cracks and reduce the performance of the joint. Therefore, promoting interface reaction is the key to achieving metallurgical connection of magnesium alloy / steel welded plates, which are difficult to dissolve and react. At present, the main means to achieve magnesium alloy / steel butt welding is to add an interlayer at the junction of magnesium alloy and steel, but its efficiency is low and the welding quality is unstable, making it difficult to achieve mass production of magnesium alloy / steel welded plates.

[0005] In view of the difficulty in welding magnesium alloy / steel tailor-welded plates, which are difficult to dissolve and non-react dissimilar metals, the present invention proposes to pre-set a transition layer in the thickness direction of the steel side parent material before welding the magnesium alloy / steel tailor-welded plates, and realize the weld tracking of the magnesium alloy / steel by an intelligent welding robot, accurately control the laser offset, and then use a laser-arc composite heat source to perform butt melting welding on the magnesium alloy / steel tailor-welded plates. The laser mainly acts on the transition layer and the steel side, and the arc mainly acts on the magnesium alloy side, so as to realize the melting welding of the magnesium alloy / steel tailor-welded plates, solve the problems of low welding efficiency and unstable welding quality of the magnesium alloy / steel tailor-welded plates, and realize high-performance welding of the magnesium alloy / steel tailor-welded plates. Summary of the invention

[0006] The purpose of the present invention is to provide a common solution to the problems of insufficient interface reaction of magnesium alloy / steel tailor-welded blanks, uneven transition layer, unstable welding quality, and difficulty in mass production. A transition layer is pre-set in the thickness direction of the steel side parent material, and the thickness and type of the transition layer are regulated to promote the magnesium alloy / steel interface reaction; an intelligent welding robot is used to achieve weld tracking, and the laser offset is accurately controlled to achieve the regulation of the steel melting amount; and the laser-arc hybrid welding method is used to promote sufficient interface reaction while ensuring the joint forming quality to achieve the metallurgical connection of magnesium alloy / steel tailor-welded blanks.

[0007] To achieve the above-mentioned purpose, the technical solutions adopted by the present invention are: magnesium alloy / steel tailor-welded plate welding transition layer preparation technology, intelligent welding robot weld tracking, and magnesium alloy / steel tailor-welded plate laser-arc composite heat source welding method based on transition layer preparation and weld tracking technology.

[0008] Before welding magnesium alloy / steel tailor-welded plates, the transition layer preparation method is: spraying, including plasma spraying, flame spraying, supersonic spraying, etc.

[0009] Furthermore, the types of transition layers include the following categories: 1. Pure metal over-plating layer; 2. Alloy transition layer.

[0010] There are two types of pure metal over-plating: one is the element that can infinitely dissolve with Fe, such as Ni, Co, Cr, etc.; the other is the element that can react with Fe and Mg but cannot infinitely dissolve with Fe, such as Cu, Zn, Sn, etc.

[0011] The alloy elements in the alloy transition layer can react with Fe and Mg, such as Cu-Zn alloy, Cu-Sn alloy, etc.

[0012] The transition layer is a single-layer structure with a micrometer scale and a thickness of 30-500 μm.

[0013] Magnesium alloy / steel tailor-welded plates, the thickness of the magnesium alloy plate is greater than that of the steel plate. During the magnesium alloy / steel butt welding fusion welding process, the magnesium alloy burns more, and the burning loss of the magnesium alloy is compensated by increasing the thickness of the magnesium plate.

[0014] Magnesium alloy / steel tailor-welded plate weld recognition and automatic tracking technology. The weld tracking system can accurately identify the side position of the steel, and its weld offset accuracy is up to 0.05 mm. By controlling the laser power and laser offset, the melting amount of the steel can be accurately controlled while other parameters remain unchanged.

[0015] The welding method of magnesium alloy / steel tailor welded plates is laser-arc hybrid welding, which performs butt melting welding on magnesium alloy / steel tailor welded plates. The laser mainly acts on the transition layer and the steel side, and the arc mainly acts on the magnesium alloy side to achieve butt melting welding of magnesium alloy / steel. The welding method of magnesium alloy / steel tailor welded plates also includes other welding methods that use spraying to place the transition layer between two dissimilar materials and achieve metallurgical connection.

[0016] The purpose of the present invention is to provide a method for preparing a transition layer of a magnesium alloy / steel tailor-welded plate, and based on the intelligent welding robot weld tracking technology, accurately control the laser offset, improve the welding quality stability, and adopt a laser-arc hybrid welding method to prepare a magnesium alloy / steel tailor-welded plate. The preparation method has a simple process and a wide range of applications, and is convenient for large-scale batch production of difficult-to-solubilize and non-reactive dissimilar metal alloy / steel tailor-welded plates.

[0017] Compared with the existing dissimilar metal connection technology, the present invention has the following advantages: it solves the problem of low efficiency and unstable welding quality caused by manually adding alloy interlayers during the welding process of magnesium alloy / steel tailor-welded plates, and can achieve uniform spraying of the transition layer and mass production. By pre-setting the transition layer in the thickness direction of the steel side parent material, the laser offset is accurately controlled based on the weld tracking technology of the intelligent welding robot, and the laser-arc melting welding method is used to achieve the metallurgical connection between the transition layer and the parent materials on both sides, wherein the type and thickness of the transition layer are adjustable, and the weld structure and joint mechanical properties are regulated by controlling the melting amount of the steel parent material and the magnesium alloy during the welding process. The present invention can meet the welding requirements of structures such as butt joints, lap joints and T-joints. DETAILED DESCRIPTION

[0018] In the following, the magnesium alloy / steel tailor-welded blank welding method based on transition layer preparation is described in detail. In addition, the transition layer preparation method, the magnesium alloy / steel tailor-welded blank connection method based on pre-prepared transition layer, and the type of base material selected for welding are not limited by the following specific implementation methods.

[0019] The transition layer mainly includes the following two types:

[0020] The first transition layer structure: pure metal overplating. There are two types of pure metal overplating: one is the element that can be infinitely dissolved in Fe, such as Ni, Co, Cr, etc.; the other is the element that can react with Fe and Mg but cannot be infinitely dissolved in Fe, such as Cu, Zn, Sn, etc.

[0021] The second transition layer structure: alloy transition layer. The alloy elements in the alloy transition layer can react with Fe and Mg, such as Cu-Zn alloy, Cu-Sn alloy, etc.

[0022] Example 1, a method for laser-arc hybrid welding of magnesium alloy / steel tailor-welded blanks sprayed with Ni transition layer based on an intelligent welding robot, the steps are as follows:

[0023] Firstly, the widely used AZ31B magnesium alloy sheet and automotive DP800 high-strength steel sheet were selected as heterogeneous metal joining materials, with thicknesses of 1.5 mm and 1.0 mm respectively.

[0024] Step 1: Cleaning the side of the steel plate

[0025] The side of the DP800 high-strength steel plate was polished with 1500# sandpaper, and then pickled with a 5% sulfuric acid aqueous solution to remove the oxide scale and rust on the side of the steel plate. Then, it was wiped with 95% industrial alcohol to obtain a clean and exposed steel plate on the side and surface.

[0026] Step 2: Sandblasting of the steel plate side

[0027] The side of the steel plate is roughened under a certain sandblasting pressure, and the treated sample is fixed on the fixture.

[0028] Step 3: Spray pure Ni transition layer on the side of the steel plate

[0029] High-purity Ni powder with a particle size of 30 μm was selected and dried in a drying oven at 100°C for 2 h. Pure Ni powder was sprayed on the side of DP800 high-strength steel plate using plasma spraying technology, with a spraying voltage of 50-60 V, a spraying current of 400-500 A, a powder feeding gas flow rate of 5-8 L / min, a spraying distance of 70-130 mm, and a pure Ni transition layer thickness of 30-500 μm.

[0030] Step 4: Surface treatment of magnesium plate

[0031] Use 1500# sandpaper to grind the surface and side of the AZ31B magnesium alloy plate to be welded to remove the oxide scale and oil stain on the surface of the magnesium alloy plate to be welded, and then choose 95% industrial alcohol to wipe the magnesium alloy plate to obtain a clean and completely exposed magnesium alloy plate.

[0032] Step 5: Magnesium alloy / steel tailor-welded blank weld identification and automatic tracking technology

[0033] The center of the laser spot is placed on the side of the steel, and the laser offset is defined as 0 mm. The center of the laser spot is offset to the inside of the steel, which is defined as a positive offset, and the center of the laser spot is offset to the magnesium side, which is defined as a negative offset.

[0034] The weld tracking system accurately identifies the position of the steel side, and its weld offset accuracy reaches 0.05 mm. During the welding process, the laser offset is adjusted every 0.1 mm. By controlling the laser power and laser offset, the melting amount of steel and magnesium alloy can be accurately controlled while other parameters remain unchanged.

[0035] Step 6: Laser-arc butt fusion welding of magnesium alloy / steel tailor-welded blanks

[0036] A DP800 high-strength steel plate with a 100 μm thick pure Ni transition layer pre-set on the side was laser-arc butt-melting welded to an AZ31B magnesium alloy plate with a TIG current of 30-50 A, a laser power of 800-2000 W, a welding speed of 600-1200 mm / min, and an argon gas flow rate of 10-20 L / min.

[0037] Example 1 According to the selected transition layer type, plasma spraying technology is used to directly prepare DP800 steel with a transition layer on the side. Through the process parameters in plasma spraying, transition layers of different thicknesses are prepared, and the thickness of the transition layer is controlled at 30~500 μm. Laser-arc hybrid welding technology is used to weld magnesium alloy / steel tailor-welded plates. Since Ni and Fe are infinitely dissolved, and Ni can react with Mg, the melting amount of steel is controlled by setting the laser offset, thereby regulating the weld structure and joint performance, and finally the magnesium alloy / steel tailor-welded plates are connected with high performance.

[0038] The magnesium alloy / steel tailor-welded plate specimens obtained when the pure Ni transition layer was 100 μm had a better joint by double-sided welding method, and the tensile strength of the joint was as high as 195 MPa. The joint broke at the magnesium alloy / steel interface, and the joint structure was magnesium alloy / interface layer / Fe-Ni solid solution / steel; when the thickness of the pure Ni transition layer was 50 μm, the joint structure was magnesium alloy / interface layer / Fe-Ni solid solution / steel, and its tensile strength was 168 MPa; when the thickness of the pure Ni transition layer was 200 μm, a large amount of Mg-Ni eutectic appeared in the weld, affecting the joint performance, and its tensile strength was 132 MPa.

[0039] Example 2, the welding method of magnesium alloy / steel tailor-welded blanks with laser-arc hybrid welding and Ni interlayer is as follows:

[0040] Firstly, the widely used AZ31B magnesium alloy sheet and DP800 high-strength steel sheet for automobiles were selected as heterogeneous metal connection materials, with thicknesses of 1.5 mm and 1.0 mm, lengths of 100 mm and widths of 50 mm, respectively.

[0041] Step 1: Cleaning the side of the steel plate

[0042] The side of the DP800 high-strength steel plate was polished with 1500# sandpaper, and then pickled with a 5% sulfuric acid aqueous solution to remove the oxide scale and rust on the side of the steel plate. Then, it was wiped with 95% industrial alcohol to obtain a clean and exposed steel plate on the side and surface.

[0043] Step 2: Preset Ni interlayers of different thicknesses and widths

[0044] Ni foils with thicknesses of 50 μm, 100 μm and 200 μm were selected respectively, and according to the test plate specifications, a paper cutting machine was used to cut the Ni interlayer with a length of 100 mm and a width of 1 mm.

[0045] Step 3: Pretreatment of Ni interlayer and fixation on the side of steel plate

[0046] The Ni interlayer cut by the paper cutter is narrow in width, bends, and curls back, and cannot be fixed on the side of the steel. The Ni interlayer is placed in a heat treatment furnace and kept at 1000°C for 0.5 h. The surface oxide is then removed and the interlayer is corrected to obtain a straight Ni interlayer, which is finally fixed on the side of the steel plate.

[0047] Step 4: Positioning the welding position of magnesium alloy / steel tailor-welded plates

[0048] The magnesium alloy and steel are fixed on the fixture, and the Ni interlayer is located at the joint of the magnesium alloy and the steel plate. The laser acts on the magnesium alloy / steel junction. The laser offset is controlled by adjusting the bottom translation stage. The laser offset is adjusted every 0.1 mm during the welding process. By controlling the laser power and laser offset, the melting amount of steel and magnesium alloy can be controlled while other parameters remain unchanged.

[0049] Step 5: Laser-arc butt fusion welding of magnesium alloy / steel tailor-welded plates

[0050] The DP800 high-strength steel plate with a 100 μm thick pure Ni interlayer and the AZ31B magnesium alloy plate were butt-melted by laser-arc welding. The TIG current was 30-50 A, the laser power was 800-2000 W, the welding speed was 600-1200 mm / min, and the argon flow rate was 10-20 L / min.

[0051] Compared with Example 1, the interlayer preparation method of Example 2 has an uneven interlayer width, and is prone to rewinding after cutting with a paper cutting machine, which increases the subsequent processing process. When the Ni interlayer is fixed on the steel side after preparation, the width and straightness of the Ni interlayer cannot be ensured to be completely consistent, and it is completely fitted to the steel side, which will directly affect the subsequent welding quality. Therefore, Example 1 uses a thermal spraying method to obtain a Ni transition layer with uniform thickness and width and close fitting, which can further improve the stability of welding quality; during the welding process of magnesium alloy / steel tailor-welded plates, the laser offset is an important factor affecting the welding formation, and the laser offset control accuracy is required to be high. Example 2 adjusts the laser offset by direct observation and manual adjustment, which further aggravates the instability of welding quality. Example 1 accurately identifies the steel side position through a weld tracking system, and its weld offset accuracy is 0.05mm. During the welding process, the laser offset is adjusted every 0.1 mm to accurately control the melting amount of steel and magnesium alloy; through the preset interlayer preparation method and the laser cheap control method, it will provide technical guarantee for the automated production of magnesium alloy / steel tailor-welded plate melting welding.

[0052] 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 for tailor-welded plates of dissimilar metals, characterized in that: The method comprises the following steps: The first step is cleaning; Grind the welding surface of the steel plate, pickle the sides and surface of the steel plate to remove the scale and rust on the surface of the steel plate, and wipe with alcohol to obtain a clean and bare steel plate on the sides and surface; Step 2: Sandblasting of steel plate; The welding surface of the steel plate is roughened by sandblasting, and the treated sample is fixed on the fixture; The third step is to spray the transition layer on the steel plate; The pure Ni powder was sprayed on the welding surface of the steel plate by plasma spraying technology, with a spraying voltage of 50-60 V, a spraying current of 400-500 A, a powder feeding gas flow rate of 5-8 L / min, a spraying distance of 70-130 mm, and a pure Ni transition layer thickness of 30-500 μm. Step 4: Treatment of the side of the magnesium plate and the surface to be welded; Grind the side surface and the surface to be welded of the magnesium alloy plate to remove the scale and oil stains on the side surface and the surface to be welded of the magnesium alloy plate, and wipe the magnesium alloy plate with alcohol to obtain a clean and completely exposed magnesium alloy plate; Step 5: Weld seam trajectory identification and tracking; The steel plate with a pure Ni transition layer pre-set on the side is butted against the magnesium alloy plate and fixed on the fixture. The intelligent welding robot with machine vision has a lateral accuracy of 0.05 mm. Step 6: Laser-arc hybrid butt fusion welding of magnesium alloy / steel tailor-welded plates; After the motion trajectory is set, the laser offset to the base materials on both sides, the laser power and the welding speed are set to achieve the forming of magnesium alloy / steel tailor-welded blanks; The laser-arc hybrid welding method is adopted. The high-energy-density laser acts on the steel side, and the melting amount of the steel is controlled by adjusting the laser offset. The low-energy-density arc acts on the magnesium alloy side to compensate for the burning of the magnesium alloy in the laser radiation area.

2. The welding method of dissimilar metal tailor-welded blanks according to claim 1, characterized in that: The thickness of the transition layer is 30-300 μm.

3. The welding method of dissimilar metal tailor-welded blanks according to claim 2, characterized in that: The thickness of the transition layer is 100 μm.

4. The welding method of dissimilar metal tailor-welded blanks according to claim 1, characterized in that: The TIG current of the laser-arc hybrid butt fusion welding is 30-50 A, the laser power is 800-2000 W, the welding speed is 600-1200 mm / min, and the argon gas flow rate is 10-20 L / min.

5. The welding method of dissimilar metal tailor-welded blanks according to claim 1, characterized in that: During the welding process, the steel plate and the magnesium plate are butt-jointed, and the thickness of the magnesium plate is greater than that of the steel plate.

6. The welding method of dissimilar metal tailor-welded blanks according to claim 1, characterized in that: At the same time, two welding methods, single-sided welding and double-sided welding, are used. When single-sided welding is used, ensure that the back of the steel is fully melted. When double-sided welding is used, the steel can be fully melted in two times. If the back steel of the single-sided welding is not melted, the double-sided welding method is used to perform laser-arc hybrid welding on the back until the steel is completely melted in the thickness direction.