Friction stir welding method for metal composite plate

Abstract

The invention belongs to the technical field of metal welding, and particularly relates to a friction stir welding method for a metal composite plate, which comprises the following process steps of: (1) surface treatment of a butt joint surface: cleaning the butt joint surface until the surface is free of dust and oil stain, and polishing; (2) cold spraying of an intermediate coating: spraying the intermediate coating on the butt joint surface polished in the step (1) by cold spraying; (3) intermediate layer polishing: after the cold spraying coating in the step (2) is cooled, carrying out surface polishing; (4) the metal composite plates are fixed, specifically, the two metal composite plates to be welded are fixed through clamps, and the butt joint faces of the two metal composite plates are attached; and (5) welding is conducted, specifically, the butt joint faces of the two metal composite plates in the previous step are welded through friction stir welding. The welding method is easy and convenient to operate and high in deposition efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of metal welding, and in particular relates to a method for friction stir welding of metal composite plates. Background Art

[0002] Friction stir welding is a new type of welding technology. It uses the heat generated by the friction between the high-speed rotating stirring needle and the workpiece to partially melt the welded material. The weld thickness can be 3-15mm. During the welding process, a stirring needle of a specific length is inserted into the weld under high-speed rotation. Since the high-speed rotating stirring needle will generate heat with the workpiece and cause the metal to soften, the material around the stirring needle will undergo severe plastic deformation. When the welding tool moves forward along the welding interface, the plasticized material flows from the front to the back of the welding tool under the action of the rotating friction of the welding tool, and forms a dense solid phase weld under the extrusion of the welding tool. The welded joint of stir friction welding has high strength, stable and reliable quality, and no filling materials such as welding wire and flux are required during the welding process, and no shielding gas is required, so the material consumption is small and the cost is low. Stir friction welding is suitable for various materials with poor weldability, such as aluminum alloy, magnesium alloy, titanium alloy, etc., and the welding joint performance is excellent. Therefore, both in theory and in practice, friction stir welding is a very suitable welding technology for composite plate welding. However, due to the complex composition of the composite plate, taking copper / aluminum composite plate welding as an example, due to the large difference between copper and aluminum in physical, chemical and mechanical properties, defects such as pores and heat-affected zones are easily generated during the welding process. In addition, copper-aluminum intermetallic compounds will be formed under high-speed stirring of the stirring needle, which will reduce the strength of the weld.

[0003] After searching, there is a prior art Chinese patent CN108385101A, a stir friction welding weld online cold spray protection and enhancement technology, which discloses a stir friction welding weld online cold spray protection and enhancement technology. The technology adopts a method of online compounding of cold spraying and stir friction welding to effectively avoid welding thinning and improve the weak bonding and brittleness of the existing cold spray coating, thereby achieving the technical effect of simultaneously improving the surface protection and mechanical properties of the weld, and coexisting high performance and lightweight structure, and then developing a method that is more suitable for corrosion protection and mechanical property enhancement of stir friction welding joints. Although both are stir friction welding, the technical problems solved by this patent and the technical solutions adopted are different from the research of the applicant. Summary of the invention

[0004] The present invention provides a method for stir friction welding of metal composite plates. An intermediate layer is added between the composite plates. The added intermediate layer is required to be miscible with the substrate elements, so that the brittle bonding layer becomes thinner, which is beneficial to improving the welding performance of the joint. The intermediate layer is added mainly by metal cold spraying technology to spray the intermediate layer on the butt surface of the two composite plates to be welded before welding. This method is simple and convenient to operate and has high deposition efficiency. Specifically, it is a welding method for stir friction welding of copper / aluminum metal composite plates. The intermediate layer elements that can be added include erbium, nickel, zinc, etc., but considering that rare earth elements are relatively precious, zinc is the best choice. At the same time, zinc can also be used for the welding intermediate layer of aluminum / magnesium and aluminum / steel composite plates. This is the research conclusion obtained by the applicant after research.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for friction stir welding of metal composite plates comprises the following steps:

[0007] (1) Surface treatment of the butt joint: clean the butt joint surface until there is no dust or oil on the surface and then polish it;

[0008] (2) Cold spraying intermediate layer: using cold spraying to spray an intermediate coating on the butt joint surface after grinding in step (1);

[0009] (3) Intermediate layer grinding: After the cold spray coating in step (2) is cooled, surface grinding is performed;

[0010] (4) Fixing the metal composite plates: Fix the two metal composite plates to be welded with clamps respectively, and fit the butt surfaces of the two metal composite plates together;

[0011] (5) Welding: The butt surfaces of the two metal composite plates in the above step are welded by friction stir welding.

[0012] Further explanation: in step (1) and step (3), the grinding is performed using sandpaper or an angle grinder; in step (1), the grinding is performed by grinding the butt joint surface until there are no protrusions visible to the naked eye and then using a hair dryer to blow away the powder and debris produced by grinding on the surface; in step (3), the grinding is performed by grinding the sprayed intermediate layer on the butt joint surface of the two metal composite plates to 0.1 mm, and the surface is flat and smooth.

[0013] Further description: in step (1), the cleaning of the docking surface is performed using an ultrasonic cleaning apparatus.

[0014] Further explanation: in step (2), when the cold spray is applied, the angle between the spray gun and the butt joint surface should be as vertical as possible and should not be less than 45°. If the spraying thickness is required to be greater than the maximum coating thickness of the spraying equipment, before spraying each layer, ensure that the coating is fully dried and cured.

[0015] Further, in step (5), the thickness of the metal composite plate is 5-15 mm, and the parameters of the stir friction welding are set as follows: the rotation speed is 400-1200 rpm, the welding speed is 10-60 mm / min, and the shoulder pressure is 0.1-0.5 mm.

[0016] Further explanation, in step (5), after the parameter setting of the stir friction welding is completed, the stirring needle first starts to penetrate from one end. According to the previously set welding depth, the stirring needle will penetrate to a specified depth of 6.5-9.5 mm, and the axis will be pressed down to 0.1 mm from the surface of the substrate, in close contact with the surface of the substrate, and preheated at the starting point for 4 seconds. After the material around the weld reaches the welding temperature and plastic state, the stirring needle moves forward to leave the weld to the edge. The welding is completed, and the stirring needle is lifted to leave a keyhole at the weld.

[0017] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0018] The present invention adds an intermediate layer between the composite plates, and requires that the added intermediate layer can be mutually soluble with the substrate elements, so that the brittle bonding layer becomes thinner, which is beneficial to improving the welding performance of the joint. The intermediate layer is mainly added by spraying the intermediate layer on the butt surface of the two composite plates to be welded before welding through the metal cold spraying technology. This method is simple and convenient to operate and has high deposition efficiency. Specifically, it is a welding method for stir friction welding of copper / aluminum metal composite plates. The intermediate layer elements that can be added include erbium, nickel, zinc, etc., but considering that rare earth elements are relatively precious, zinc is the best choice. At the same time, zinc can also be used for the welding intermediate layer of aluminum / magnesium and aluminum / steel composite plates. This is the research conclusion obtained by the applicant after research. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of welding of the present invention. Wherein, number 1 is the aluminum layer, 2 is the copper layer, 3 is the zinc interlayer, and 4 is the shaft shoulder.

[0020] Figure 2 Schematic diagram of the stirring pin used in the process of Example 2. The reference numerals 1 is the stirring pin and 2 is the shoulder.

[0021] Figure 3 It is a comparison diagram of the finished products of the welds in Example 2 and the comparative example process without the zinc interlayer.

[0022] Figure 4 Schematic diagram of the stirring pin used in the process of Examples 3 and 4. The reference numerals 1 is the stirring pin and 2 is the shaft shoulder.

[0023] Figure 5The performance diagram of the weld of the metal composite plate obtained by the welding process of the present invention is shown in FIG. Wherein the number ① is a tensile sample taken perpendicular to the weld direction, and the number ② is a cross-sectional observation area of ​​the block shown.

[0024] Figure 6 It is the cross-sectional view of the weld; a is the cross-sectional view of the weld with zinc layer added, and b is the cross-sectional view of the weld without zinc layer added. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to examples and drawings. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention. The specific steps are described as follows:

[0026] A method for friction stir welding of metal composite plates comprises the following steps:

[0027] Surface treatment of butt joint surface - spraying of intermediate layer on butt joint surface - grinding of intermediate layer surface - fixing of plate - friction stir welding

[0028] Step 1: Surface treatment of the butt joint: Use an ultrasonic cleaner to clean the butt joint surface until it is free of oil, dust and other pollutants, and then grind the butt joint surfaces of the two metal composite plates to be welded (hereinafter collectively referred to as A plate and B plate) to make their surfaces smooth without protrusions or depressions, and increase the surface roughness to improve the deposition efficiency of particles in the subsequent cold spraying process.

[0029] Step 2, cold spraying intermediate layer: Use metal cold spraying technology to spray the intermediate layer on the butt joint surface of plate A and plate B after grinding, and the thickness of the sprayed intermediate layer must be consistent. The specific thickness needs to be determined according to the thickness, composition, and performance of the specific metal composite plate, and the spraying parameters must also be set according to the performance of the selected spraying particles. When spraying, the angle between the spray gun and the butt joint surface should be as vertical as possible and must not be less than 45° to ensure that the particles can be sprayed vertically onto the butt joint surface, improve the uniformity and bonding strength of the sprayed intermediate layer, and observe the formation of the sprayed intermediate layer. If the spraying thickness needs to be greater than the maximum coating thickness of the spraying equipment, ensure that the coating is fully dried and cured before spraying each layer.

[0030] Step 3, grinding the middle layer: After the sprayed middle layer obtained in step 2 cools down, use sandpaper or an angle grinder to grind the surface of the sprayed middle layer. Since the coating surface obtained by the existing cold spraying technology is mostly corrugated and has low flatness, it is necessary to use sandpaper or other grinding equipment to grind its surface flat, so that when clamping and fixing in the later stage, the two sides of the butt joint can be closely fitted, avoiding the large gap between the two butt joint surfaces that affects the welding quality.

[0031] Step 4: Fix the metal composite plate: Fix the two composite plates A and B to be welded with clamps respectively. When fixing, ensure that the two butt surfaces fit tightly. Figure 1 As shown. When the gap exceeds a certain extent, it will be difficult for the metal to fill the weld gap, thus forming defects such as grooves or holes in the weld. These defects will weaken the strength and toughness of the weld and reduce the overall performance of the welded joint. In addition, during the friction stir welding process, if the thickness difference of the materials to be welded is large, the existence of the gap may cause flash to form on one side of the thick plate. Flash not only affects the aesthetics of the weld, but may also increase the cost and difficulty of the subsequent flash removal process. Therefore, the grinding in step three and the clamping in this step should minimize the gap.

[0032] Step 5: Welding: Start welding (such as Figure 1 When welding, pay attention to the adjustment of welding parameters, including rotation speed, travel speed (i.e. welding speed) and shoulder (such as Figure 1 - Shoulder) pressure, especially for the welding of dissimilar metals, it is necessary to consider the comprehensive influence of multiple factors when setting parameters. In actual operation, it is necessary to set and adjust according to different welding material characteristics and welding requirements, and the stirring needle needs to be specially designed when necessary. In this patent, for the welding of copper / aluminum composite plates with a thickness of 5-15mm, the rotation speed is generally set to: 400-1200rpm, the welding speed is 10-60mm / min (the slower the speed, the more conducive to plastic deformation and flow of the material, and improves the uniformity of the weld composition), and the shoulder pressure is 0.1-0.5mm.

[0033] Example 1

[0034] In this example, the A metal composite plate and the B metal composite plate are both made of copper / aluminum composite plates (T2+1060) prepared by explosive composite method. The overall size of A and B is 150mm*80mm*7mm, and the thickness of each layer from top to bottom is: copper layer 3mm, aluminum layer 4mm. The middle interlayer is made of zinc powder with a particle size of 20-50 microns and a thickness of 0.2mm.

[0035] Pretreatment of the joint surface of A and B metal composite plates: Use DL-720D intelligent ultrasonic cleaner to clean the joint surfaces of A and B metal composite plates until the surface is smooth and free of oil and dust. After drying, use an angle grinder to grind the joint surfaces (150mm*7mm) until there are no visible protrusions on the surface. Use a hair dryer to blow away the powder and debris produced by grinding on the surface to avoid affecting the deposition of subsequent cold spray particles.

[0036] Cold spraying of butt joint surface: The spraying equipment selected in this case is Tianchengyu supersonic low-pressure cold spraying device. First, fix the copper / aluminum composite plate, align the polished and cleaned butt joint surface with the spray gun of the cold spraying device, start the equipment randomly, turn on the gas supply system (compressed gas is air in this case according to the characteristics of zinc particles), adjust to the set gas pressure (0.8MPa) and flow rate (20g / min), and then turn on the powder feeder and spray gun to ensure that the powder can be stably transported to the spray gun. When spraying, keep the spray gun vertically aligned with the butt joint surface, and keep the distance between the spray gun and the butt joint surface at 150mm. This distance can ensure that the zinc powder can be sprayed evenly and effectively to the butt joint surface to form a uniform spraying intermediate layer. The moving speed of the spray gun is controlled at 150mm / s. In order to maintain the stability of the spraying process, a robotic arm is used in this case to complete the automatic spraying of the butt joint surface. The butt joint surface spraying of the two metal composite plates A and B is the same.

[0037] Surface grinding of the sprayed intermediate layer: The thickness of the intermediate layer obtained after spraying is 0.3 mm, and the surface is corrugated, so a grinder is subsequently used to grind the sprayed intermediate layer on the butt joint surfaces of the two metal composite plates A and B to 0.1 mm, and the surface is flat and smooth.

[0038] Welding: The stirring needle used in this example is Figure 2 As shown, the length of the stirring needle used is 6.5mm. Before welding, the two metal composite plates A and B are rigidly fixed on the fixture in a flat butt joint manner. The butt joint surfaces are required to be in close contact and there is no obvious gap in the middle. Turn on the equipment to complete the parameter setting: ① Set the speed of the stirring needle to 900rpm. Recommendation: In general, the speed of the stirring needle is set between 900-2000rpm. When the rotation speed of the stirring needle is lower than 400rpm, the welding of the copper / aluminum composite plate butt joint cannot be achieved; and when the rotation speed is greater than 1200rpm, the welder will jitter, affecting the welding quality. Therefore, a more specific speed range needs to be adjusted according to the actual welding situation and equipment performance, but it is usually recommended to select within the range of 400-1200rpm or 600-1400rpm. ② The travel speed of the stirring needle, that is, the welding speed, is set to 50mm / min, and ③ the inter-axis downward pressure is 0.1mm. After completing the parameter setting, the stirring needle first starts to penetrate from one end. According to the previously set welding depth, the stirring needle will penetrate to the specified depth of 6.5mm, and the axis will be pressed down to 0.1mm from the surface of the substrate, in close contact with the surface of the substrate, and preheated at the starting point for 4 seconds. After the material around the weld reaches the welding temperature and plastic state, the stirring needle moves forward and leaves the weld to the edge. The welding is completed, and the stirring needle is lifted to leave a keyhole at the weld.

[0039] The comparison of the finished product prepared in Example 1 and the weld without zinc interlayer is shown in the figure below. Figure 3Here, zinc can increase the fluidity of the material, promote the tightness of the weld, fill the gaps in the weld, form a continuous interactive structure and react with the substrate to generate Al 0.4 Zn 0.6 , CuZn and Cu5Zn8 and other compounds, thereby inhibiting the formation of copper-aluminum intermetallic compounds to a certain extent, and forming a weld with a smooth surface and high fusion degree with the matrix, such as Figure 3 As shown, a is a weld without zinc interlayer, and b is a weld with sprayed zinc intermediate layer, both of which are welded under the same process parameters.

[0040] Example 2

[0041] Comparative Example 1: In this example, the A and B metal composite plates are made of copper / aluminum / copper composite plates (T2+1060+T2) prepared by explosive composite method as welding objects. The overall size of the A and B metal composite plates is 150mm*80mm*10mm, and the thickness of each layer from top to bottom is: copper layer 3mm, aluminum layer 4mm, copper layer 3mm. The middle layer is made of zinc powder with an average particle size of 30 microns and a thickness of 0.3mm.

[0042] Pretreatment of the joint surface of A and B metal composite plates: Use DL-720D intelligent ultrasonic cleaner to clean the joint surfaces of A and B metal composite plates until the surface is smooth and free of oil and dust. After drying, use an angle grinder to grind the joint surface (150mm*10mm) until there are no visible protrusions on the surface. Use a hair dryer to blow away the powder and debris produced by grinding on the surface to avoid affecting the deposition of subsequent cold spray particles.

[0043] Cold spraying of the butt joint surface: The spraying equipment selected in this case is the Tianchengyu supersonic low-pressure cold spraying device. First, fix the copper / aluminum / copper composite plate, align the butt joint surface to be sprayed with the spray gun of the cold spraying device, start the equipment randomly, turn on the gas supply system (according to the characteristics of zinc particles, compressed gas is air in this case), adjust to the set gas pressure (0.8MPa) and flow rate (20g / min), and then turn on the powder feeder and spray gun to ensure that the powder can be stably transported to the spray gun. When spraying, keep the spray gun vertically aligned with the butt joint surface, and keep the distance between the spray gun and the butt joint surface at 150mm. This distance can ensure that the zinc powder can be sprayed evenly and effectively to the butt joint surface to form a uniform spraying middle layer. The moving speed of the spray gun is controlled at 150mm / s. In order to maintain the stability of the spraying process, a robotic arm is used for automatic spraying in this case. The spraying of the middle layer of the butt joint surface of the two metal composite plates A and B is the same.

[0044] Surface grinding of the sprayed intermediate layer: The thickness of the intermediate layer obtained after spraying is 0.3mm, and the surface is corrugated, so a grinder is used to grind the sprayed intermediate layer on the butt joint surface of the two metal composite plates A and B to 0.15mm, and the surface is flat and smooth.

[0045] Welding: The stirring needle used in the friction stir welding in this example is Figure 4 As shown, the length of the stirring needle used is 9.5mm. Before welding, the two metal composite plates A and B are rigidly fixed on the fixture in a flat butt joint manner. The butt joint surfaces are required to be in close contact and there is no obvious gap in the middle. Turn on the equipment to complete the parameter setting: ① Set the speed of the stirring needle to 900rpm. ② The travel speed of the stirring needle, that is, the welding speed, is set to 50mm / min, and ③ The amount of pressure between the axes is 0.1mm. After completing the parameter setting, the stirring needle first starts to penetrate from the starting point at one end. According to the previously set welding depth, the stirring needle will penetrate to the specified depth of 9.5mm, and the axis will be pressed down to 0.1mm from the surface of the substrate, closely contacting the surface of the substrate, and preheating at the starting point for 4 seconds. After the material around the weld reaches the welding temperature and plastic state, the stirring needle moves forward to leave the weld to the edge. The welding is completed, and the stirring needle is lifted, leaving a keyhole at the weld.

[0046] Example 3:

[0047] Comparative Example 1 and Example 2, in this example, the A and B metal composite plates are aluminum / copper / aluminum composite plates (1060+T2+1060) prepared by explosive composite method as welding objects, the overall size of the A and B metal composite plates is 150mm*80mm*10mm, and the thickness of each layer from top to bottom is: aluminum layer 3mm, copper layer 4mm, aluminum layer 3mm. The middle layer is selected from zinc powder with an average particle size of 30 microns and a thickness of 0.3mm.

[0048] Pretreatment of the butt joint of metal composite plates: Use DL-720D intelligent ultrasonic cleaner to clean the butt joint of metal composite plates A and B until the surface is smooth and free of oil and dust. After drying, use an angle grinder to grind the butt joint (150mm*10mm) until there are no visible protrusions on the surface. Use a hair dryer to blow away the powder and debris produced by grinding on the surface to avoid affecting the deposition of subsequent cold spray particles.

[0049] Cold spraying of butt joint surface: The spraying equipment selected in this case is Tianchengyu supersonic low-pressure cold spraying device. First, fix the aluminum / copper / aluminum composite plate, align the butt joint surface to be sprayed with the spray gun of the cold spraying device, start the equipment randomly, turn on the gas supply system (according to the characteristics of zinc particles, compressed gas is air in this case), adjust to the set gas pressure (0.8MPa) and flow rate (20g / min), and then turn on the powder feeder and spray gun to ensure that the powder can be stably transported to the spray gun. When spraying, keep the spray gun vertically aligned with the butt joint surface, and keep the distance between the spray gun and the butt joint surface at 150mm. This distance can ensure that the zinc powder can be sprayed evenly and effectively on the butt joint surface to form a uniform intermediate layer. The moving speed of the spray gun is controlled at 150mm / s. In order to maintain the stability of the spraying process, a robotic arm is used for automated spraying in this case. The butt joint surfaces of the two metal composite plates A and B are sprayed the same.

[0050] Surface grinding of the sprayed intermediate layer: The thickness of the intermediate layer obtained after spraying is 0.3 mm, and the surface is corrugated, so a grinder is subsequently used to grind the intermediate layer on the butt joint surface of the two metal composite plates A and B to 0.15 mm, and the surface is flat and smooth.

[0051] Welding: The stirring needle used in this example is Figure 4 As shown, the length of the stirring needle used is 9.5mm. Before welding, the two metal composite plates A and B are rigidly fixed on the fixture in a flat butt joint manner. The butt joint surfaces are required to be in close contact and there is no obvious gap in the middle. Turn on the equipment to complete the parameter setting: ① Set the speed of the stirring needle to 900rpm. ② The travel speed of the stirring needle, that is, the welding speed, is set to 50mm / min, and ③ The amount of pressure between the axes is 0.1mm. After completing the parameter setting, the stirring needle first starts to penetrate from the starting point at one end. According to the previously set welding depth, the stirring needle will penetrate to the specified depth of 9.5mm, and the axis will be pressed down to 0.1mm from the surface of the substrate, closely contacting the surface of the substrate, and preheating at the starting point for 4 seconds. After the material around the weld reaches the welding temperature and plastic state, the stirring needle moves forward to leave the weld to the edge. The welding is completed, and the stirring needle is lifted, leaving a keyhole at the weld.

[0052] Weld performance test:

[0053] The metal composite plate welded under this process is taken with the weld as the center and a tensile specimen is taken perpendicular to the weld direction. Figure 5 -① As shown in the tensile test results, the tensile strength of the weld is increased by 20% compared with the weld without zinc spraying. Figure 5 -② The block shown in the figure is observed in cross section. Figure 6 As shown, Figure 6Figure a is the cross-sectional view of the weld with a zinc layer added, and figure b is the cross-sectional view of the weld without a zinc layer added. It can be seen that the weld of the cold-sprayed zinc layer is more tightly bonded, without large cracks and gaps, and the improvement effect is obvious.

[0054] The above description is a detailed description of the preferred feasible examples of the present invention, but the examples are not used to limit the scope of the patent application of the present invention. All equivalent changes or modifications completed under the technical concept suggested by the present invention should belong to the patent scope covered by the present invention.

Claims

1. A method for friction stir welding of metal composite plates, characterized in that: The following steps are involved: (1) Surface treatment of the butt joint: clean the butt joint surface until there is no dust or oil on the surface and then polish it; (2) Cold spraying intermediate layer: using cold spraying to spray an intermediate coating on the butt joint surface after grinding in step (1); (3) Intermediate layer grinding: After the cold spray coating in step (2) is cooled, surface grinding is performed; (4) Fixing the metal composite plates: Fix the two metal composite plates to be welded with clamps respectively, and fit the butt surfaces of the two metal composite plates together; (5) Welding: The butt surfaces of the two metal composite plates in the above step are welded by friction stir welding.

2. The method for friction stir welding of metal composite plates according to claim 1, characterized in that: In step (1) and step (3), the grinding is performed using sandpaper or an angle grinder; in step (1), the grinding is performed by grinding the butt joint surface until there are no protrusions visible to the naked eye on the surface and then using a hair dryer to blow away the powder and debris produced by grinding on the surface; in step (3), the grinding is performed by grinding the sprayed intermediate layer on the butt joint surface of the two metal composite plates to 0.1 mm, and the surface is flat and smooth.

3. The method for friction stir welding of metal composite plates according to claim 1, characterized in that: In step (1), the abutment surface is cleaned using an ultrasonic cleaner.

4. The method for friction stir welding of metal composite plates according to claim 1, characterized in that: In step (2), during the cold spraying, the angle between the spray gun and the butt joint surface should be as vertical as possible and should not be less than 45°. If the required spraying thickness is greater than the maximum coating thickness of the spraying equipment, before spraying each layer, ensure that the coating is fully dried and cured.

5. The method for friction stir welding of metal composite plates according to claim 1, characterized in that: In step (5), the thickness of the metal composite plate is 5-15 mm, and the parameters of the stir friction welding are set as follows: the rotation speed is 400-1200 rpm, the welding speed is 10-60 mm / min, and the shoulder pressure is 0.1-0.5 mm.

6. The method for friction stir welding of metal composite plates according to claim 1, characterized in that: In step (5), after the parameter setting of the friction stir welding is completed, the stirring needle first starts to penetrate from one end. According to the previously set welding depth, the stirring needle will penetrate to a specified depth of 6.5-9.5 mm, and the axis is pressed down to 0.1 mm from the surface of the substrate, in close contact with the surface of the substrate, and preheated at the starting point for 4 seconds. After the material around the weld reaches the welding temperature and plastic state, the stirring needle moves forward to leave the weld to the edge. The welding is completed, and the stirring needle is lifted to leave a keyhole at the weld.

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