CMT dissimilar metal connection method for aluminum alloy and galvanized aluminum-magnesium steel

Abstract

The invention discloses an aluminum alloy and galvanized aluminum magnesium steel CMT dissimilar metal connection method. The method comprises the following steps that S11, a galvanized aluminum magnesium steel plate to be welded and an aluminum alloy plate to be welded are cleaned before welding; s12, laser etching is conducted on the surface of the cleaned zinc-aluminum-magnesium-plated steel plate, a surface microstructure is prepared, and the depth of the surface microstructure is smaller than the thickness of a plating layer on the zinc-aluminum-magnesium-plated steel plate; and S2, the galvanized aluminum magnesium steel plate with the surface microstructure and the cleaned aluminum alloy plate are placed in a lap joint mode, and welding is carried out. According to the method, the surface microstructure is prepared on the surface of the galvanized aluminum-magnesium steel plate, so that the coating restraint degree of the galvanized aluminum-magnesium steel surface is changed, the contact area of brazing filler metal and a base material is remarkably increased, the coating restraint stress of the surface of the base material is reduced, the flowing resistance of a molten pool is reduced, and the wettability is improved; the surface microstructure can promote evaporation of Zn in the coating and reduce the temperature of a molten pool, so that the thickness of an intermetallic compound is reduced, and the performance of a welded joint is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of welding, in particular to a CMT dissimilar metal connection method of aluminum alloy and galvanized aluminum magnesium steel. BACKGROUND

[0002] With the promotion of environmental regulations for lightweight, fuel efficiency improvement, or the increasing demand for corrosion-resistant materials in the construction industry, aluminum / steel connection has become a focus of research in various countries. 6061 aluminum alloy belongs to Al-Mg-Si system, has medium strength, good corrosion resistance and processing performance, and is widely used in automobile, aerospace and other fields. The galvanized aluminum magnesium steel is an alloy coating of zinc, aluminum and magnesium plated on the steel substrate, which improves the corrosion resistance, especially the notch protection capability, on the basis of the original high strength. The combination of the two can be applied to, for example, the body of the car, using aluminum alloy to reduce weight, while some structural parts need the high strength of steel, which has far-reaching significance in lightweight design.

[0003] Currently, the welding difficulties of aluminum alloy and galvanized aluminum magnesium steel mainly include the difference in melting point, the difference in thermal expansion coefficient, metallurgical incompatibility, surface treatment problem, electrochemical corrosion and the selection of suitable welding method. Especially, the plating layer on the surface of the galvanized aluminum magnesium steel is easy to evaporate or oxidize at high temperature during the welding process, which leads to the destruction of the plating layer and affects the corrosion resistance and mechanical properties of the welded joint. In addition, the existence of the plating layer changes the fluidity and wettability of the molten pool, and the traditional welding method is difficult to effectively control the influence of the plating layer on the welding process, which is easy to produce pores, cracks and other defects, and form an over-thick intermetallic compound (IMC) layer, which further reduces the joint performance.

[0004] Traditional fusion welding is easy to cause intermetallic compound and plating layer to volatilize, and it is difficult to achieve reliable connection. Mechanical connection and glue connection are often more limited by the size of the workpiece, and the reliability and production efficiency are difficult to guarantee. Therefore, CMT brazing as a new method is proposed, CMT has the advantages of low heat input, low spatter and small heat affected zone, which can effectively reduce the generation of intermetallic compound (IMC), and has outstanding advantages in thin plate welding. However, the existing CMT technology still has problems such as insufficient wettability of the filler metal and over-thick IMC layer, and innovative solutions are still needed.

[0005] Therefore, the present application mainly researches the above technical problems, especially how to optimize the behavior of the plating layer in the welding process through surface microstructure treatment, so as to improve the joint performance. SUMMARY

[0006] In view of the existing technical problems, the present application provides a CMT dissimilar metal connection method of aluminum alloy and galvanized aluminum magnesium steel to solve the problems in the prior art.

[0007] In order to achieve the above-mentioned purposes, the present application provides the following technical solutions: A CMT heterogeneous metal connection method for aluminum alloy and galvanized aluminum magnesium steel, comprising the following steps: S1, pretreating the surfaces of the aluminum alloy plate and the galvanized aluminum magnesium steel plate; The pretreatment comprises the following steps: S11, performing pre-welding cleaning on the galvanized aluminum magnesium steel plate and the aluminum alloy plate to be welded; S12, performing laser etching on the surface of the cleaned galvanized aluminum magnesium steel plate to prepare a surface microstructure, the depth of the surface microstructure being less than the thickness of the plating layer on the galvanized aluminum magnesium steel plate; S2, placing the galvanized aluminum magnesium steel plate with the surface microstructure and the cleaned aluminum alloy plate in a lap joint manner, adjusting the process parameters of the CMT welding machine, and performing welding.

[0008] Preferably, the aluminum alloy plate contains Mg 0.9 wt%, Si 0.62 wt%, Fe 0.33 wt%, Cu 0.28 wt%, Cr 0.17 wt%, Mn 0.06 wt%, Zn 0.02 wt%, and C 0.02 wt%, with the balance being Al.

[0009] Preferably, the galvanized aluminum magnesium steel plate contains Zn 15.98 wt%, Al 1.15 wt%, Mg 0.26 wt%, and Si 0.08 wt%, with the balance being Fe.

[0010] Preferably, the surface microstructure is a groove-type surface microstructure, the depth of the groove-type surface microstructure being 15-25 μm, and the spacing between the groove-type surface microstructures being 0.05-0.1 mm.

[0011] Preferably, the shape of the surface microstructure is a discrete dot array, or parallel grooves, or a cross grid, and the depth of the surface microstructure is 15-25 μm.

[0012] Preferably, the process parameters used in the laser etching in step S12 mainly include laser power, scanning speed, scanning frequency, and scanning times, the laser power being 50 W, the scanning speed being 1500 mm / s, the scanning frequency being 30 KHz, and the scanning times being Preferably, the pre-welding cleaning process in step S11 is to use chemical reagents in combination with ultrasonic cleaning, first performing steel wire brush mechanical polishing on the aluminum alloy plate, then performing ultrasonic cleaning, and then wiping with acetone; first performing ultrasonic cleaning on the galvanized aluminum magnesium steel plate, and then wiping with acetone.

[0013] Preferably, the pre-welding cleaning process in step S11 is to use chemical reagents in combination with ultrasonic cleaning, first performing steel wire brush mechanical polishing on the aluminum alloy plate, then performing ultrasonic cleaning, and then wiping with acetone; first performing ultrasonic cleaning on the galvanized aluminum magnesium steel plate, and then wiping with acetone.

[0014] Preferably, the sequence of the lap placement in the step S2 is that the galvanizing aluminum magnesium steel plate is below, the aluminum alloy plate is above, and the lap length is mm.

[0015] Preferably, the process parameters of the CMT welding machine in the step S2 mainly include the distance between the welding torch and the workpiece, the welding speed, the wire feeding speed and the protective gas flow, the distance between the welding torch and the workpiece is 10-15 mm, the welding speed is m / min, the wire feeding speed is m / min, and the protective gas flow is L / min.

[0016] Compared with the prior art, the present application has the beneficial effects: the present application prepares the surface microstructure on the surface of the galvanizing aluminum magnesium steel plate, the technology cooperatively promotes the wetting of aluminum on the steel surface through the optimization of wetting dynamics, the regulation of interface reaction and the inhibition of crack propagation, the surface microstructure changes the constraint degree of the plated layer on the surface of the galvanizing aluminum magnesium steel, in the molten state, significantly improves the contact area of the filler metal and the base material, and makes the plated layer constraint stress on the surface of the base material decrease, so that the plated layer becomes relaxed, reduces the resistance of the molten pool flow, and improves the wettability; the surface microstructure can promote the evaporation of Zn in the plated layer, reduce the temperature of the molten pool, so that the thickness of the intermetallic compound is thinned, and the performance of the welded joint is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a schematic diagram of the CMT welding device of the aluminum alloy and the galvanizing aluminum magnesium steel in the present application; Figure 2 It is a surface topography diagram of the galvanizing aluminum magnesium steel after laser etching in the present application; Figure 3 It is a structural schematic diagram of the surface microstructure; Figure 4 It is a macroscopic topography diagram of the CMT connection implementation effect of the aluminum alloy and the untreated galvanizing aluminum magnesium steel in the present application; Figure 5 It is a macroscopic topography diagram of the CMT connection implementation effect of the aluminum alloy and the galvanizing aluminum magnesium steel after laser etching treatment in the present application; Figure 6 It is a contact angle topography diagram of the CMT connection of the aluminum alloy and the untreated galvanizing aluminum magnesium steel and the CMT connection of the aluminum alloy and the galvanizing aluminum magnesium steel after laser etching treatment in the present application; Figure 7 It is a SEM effect diagram of the joint of the CMT connection of the aluminum alloy and the untreated galvanizing aluminum magnesium steel and the CMT connection of the aluminum alloy and the galvanizing aluminum magnesium steel after laser etching treatment in the present application; Figure 8 It is a force-displacement curve diagram of the CMT connection of the aluminum alloy and the untreated galvanizing aluminum magnesium steel and the CMT connection of the aluminum alloy and the galvanizing aluminum magnesium steel after laser etching treatment in the present application. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0019] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] Assembly before welding is shown in the attached figure. Figure 1 As shown, the laser-etched galvanized aluminum-magnesium steel sheet 3 and the cleaned aluminum alloy sheet 2 are overlapped with the aluminum alloy sheet 2 on top and the galvanized aluminum-magnesium steel sheet 3 on the bottom, and fixed with a clamp 101. To ensure the firmness of the clamp 101, a shim 102 of the same thickness as the galvanized aluminum-magnesium steel sheet 3 is placed under the aluminum alloy sheet 2. The position of the CMT welding torch 7 is adjusted so that the arc beam 8 is located at the overlap seam of the laser-etched galvanized aluminum-magnesium steel sheet 3 and the cleaned aluminum alloy sheet 2. As the arc beam 8 irradiates, Ar gas is simultaneously ejected from the protective gas nozzle 9 to provide protection, thereby achieving the CMT connection between the aluminum alloy sheet 2 with surface microstructure 1 and the galvanized aluminum-magnesium steel sheet 3.

[0021] The substrates are 100mm*50mm*1.5mm aluminum alloy and galvanized aluminum-magnesium steel, and the wire material is 1.2mm diameter aluminum-silicon welding wire. The aluminum alloy contains 0.9wt% Mg, 0.62wt% Si, 0.33wt% Fe, 0.28wt% Cu, 0.17wt% Cr, 0.06wt% Mn, 0.02wt% Zn, and 0.02wt% C, with the balance being Al. The galvanized aluminum-magnesium steel contains 15.98wt% Zn, 1.15wt% Al, 0.26wt% Mg, 0.08wt% Si, with the balance being Fe.

[0022] A method for joining dissimilar metals, aluminum alloy and galvanized aluminum-magnesium steel (CMT), includes the following steps: S1, Pre-treat the surfaces of aluminum alloy sheet 2 and galvanized aluminum-magnesium steel sheet 3; The preprocessing includes the following steps: S11, the galvanized aluminum magnesium steel plate 3 to be welded and the aluminum alloy plate 2 are subjected to pre-weld cleaning; the process of pre-weld cleaning is to use chemical reagents in combination with ultrasonic cleaning, the aluminum alloy plate 2 is first subjected to mechanical polishing with a steel wire brush and then subjected to ultrasonic cleaning, and then is wiped with acetone; the galvanized aluminum magnesium steel plate 3 is first subjected to ultrasonic cleaning, and then is wiped with acetone; S12, laser etching is performed on the surface of the cleaned galvanized aluminum magnesium steel plate 3 to prepare a surface microstructure 1; the surface topography of the galvanized aluminum magnesium steel plate after laser etching can be referred to Figure 2 The process parameters for laser etching mainly include laser power, scanning speed, scanning frequency and scanning times, the laser power is 50 W, the scanning speed is 1500 mm / s, the scanning frequency is 30 KHz, and the scanning times are The depth of the surface microstructure 1 is less than the thickness of the plating layer on the galvanized aluminum magnesium steel plate 3; The surface microstructure 1 is a groove type surface microstructure, the depth of the groove type surface microstructure is 15-25 μm, the spacing between the groove type surface microstructures is 0.05-0.1 mm, and the surface microstructure 1 forms an angle with the welding direction, the angle ranges from ; of course, the shape of the surface microstructure 1 can also be a discrete dot array, or a parallel groove, or a cross grid, and the depth of the surface microstructure 1 is 15-25 μm; S2, the galvanized aluminum magnesium steel plate 3 with the surface microstructure 1 and the cleaned aluminum alloy plate 2 are overlapped and placed, and the process parameters of the CMT welding machine are adjusted to perform welding, the sequence of overlapping and placing is that the galvanized aluminum magnesium steel plate 3 is below and the aluminum alloy plate 2 is above, and the overlapping length is mm; the process parameters of the CMT welding machine mainly include the distance between the welding gun and the workpiece, the welding speed, the wire feeding speed and the protective gas flow, the distance between the welding gun and the workpiece is 10-15 mm, the welding speed is m / min, the wire feeding speed is m / min, and the protective gas flow is L / min.

[0023] Example one 100mm*50mm*1.5mm aluminum alloy and galvanized aluminum magnesium steel are used as substrates, and an aluminum-silicon welding wire with a diameter of 1.2mm is used as wire material; the aluminum alloy contains Mg0.9wt%, Si0.62wt%, Fe0.33wt%, Cu0.28wt%, Cr0.17wt%, Mn0.06wt%, Zn0.02wt%, C0.02wt%, and the balance is Al. The galvanized aluminum magnesium steel contains Zn15.98wt%, Al1.15wt%, Mg0.26wt%, Si0.08wt%, and the balance is Fe.

[0024] The embodiment provides a CMT dissimilar metal connection method of aluminum alloy and galvanized aluminum magnesium steel, and specifically comprises the following steps. S11, pre-weld cleaning is performed on the galvanized aluminum magnesium steel plate and the aluminum alloy plate to be welded; The welding materials are selected as the 1.5mm-thick galvanized aluminum magnesium steel plate 3 and the 1.5mm-thick 6061 aluminum alloy plate 2, pre-weld cleaning is performed on the galvanized aluminum magnesium steel plate 3 and the aluminum alloy plate 2 to be welded, and after the aluminum alloy plate 2 is mechanically polished by using a steel wire brush, the aluminum alloy plate 2 is wiped by using acetone; S12, laser etching is performed on the surface of the cleaned galvanized aluminum magnesium steel plate 3 to prepare a surface microstructure 1, the depth of the surface microstructure 1 is less than the thickness of the plated layer on the galvanized aluminum magnesium steel plate 3, and the depth of the surface microstructure 1 is 25μm; The cleaned galvanized aluminum magnesium steel plate 3 is subjected to laser etching by using a short-pulse nanosecond laser, the laser power is 50W, the scanning speed is 1500mm / s, the scanning frequency is 30KHz, the scanning times are 15, the scanning shape is a straight line, mainly a groove-shaped surface microstructure, the groove spacing is 0.1mm, and the groove-shaped surface microstructure is 0° with the welding direction. S2, the galvanized aluminum magnesium steel plate 3 with the surface microstructure 1 and the cleaned aluminum alloy plate 2 are overlapped and placed for assembly, and a CMT is adjusted to appropriate process parameters to perform welding; The overlapped and placed sequence is that the galvanized aluminum magnesium steel plate 3 is below and the aluminum alloy plate 2 is above, the overlapping length is 10mm, a CMT welding machine is selected as a welding power source, and after the process parameters are set as follows, welding is performed: the distance between the welding gun and the workpiece is 12mm, the welding speed is 0.3m / min, the wire feeding speed is 4.2m / min, the protective gas is Ar gas, and the flow rate is 15L / min, so that a high-quality welded joint is obtained.

[0025] In order to make a comparison, the galvanized aluminum magnesium steel plate without surface treatment and the cleaned aluminum alloy plate are welded, the remaining parameters and processes are the same as those in the above embodiment, a welded joint is obtained, the tensile shear strength of the joint is tested, and the tensile shear strength is only 183N / mm, and the joint strength is not high.

[0026] The tensile shear strength of the welded joint in the embodiment one is tested, and the tensile shear strength can reach 223N / mm, which is significantly higher than the joint strength 183N / mm without surface pretreatment, and the strength is improved by 23%.

[0027] In this embodiment, since the direction of the groove-shaped surface microstructure is parallel to the welding direction, the groove-shaped surface microstructure reduces the restraint stress of the galvannealed aluminum magnesium steel surface in the horizontal direction, and does not have a substantial promoting effect on the spread width direction of the filler metal. Therefore, the effect of improving the mechanical properties of the entire joint is limited. As can be seen, selecting a suitable angle of the groove-shaped surface microstructure is of great significance to the improvement of the joint effect.

[0028] Example Two 100mm*50mm*1.5mm aluminum alloy and galvannealed aluminum magnesium steel were used as substrates, and an aluminum-silicon welding wire with a diameter of 1.2mm was used as a wire material; the aluminum alloy contains Mg0.9wt%, Si0.62wt%, Fe0.33wt%, Cu0.28wt%, Cr0.17wt%, Mn0.06wt%, Zn0.02wt%, and C0.02wt%, with the balance being Al. The galvannealed aluminum magnesium steel plate contains Zn15.98wt%, Al1.15wt%, Mg0.26wt%, Si0.08wt%, and the balance being Fe.

[0029] The embodiment provides a CMT dissimilar metal connection method for aluminum alloy and galvannealed aluminum magnesium steel, and specifically comprises the following steps: S11, the galvannealed aluminum magnesium steel plate 3 and the aluminum alloy plate 2 to be welded are cleaned before welding; The welding materials are selected to be a 1.5mm-thick galvannealed aluminum magnesium steel plate 3 and a 1.5mm-thick 6061 aluminum alloy plate 2, the galvannealed aluminum magnesium steel plate 3 and the aluminum alloy plate 2 to be welded are cleaned before welding, the aluminum alloy plate 2 is mechanically polished by using a steel wire brush and then wiped by using acetone, and the galvannealed aluminum magnesium steel plate 3 is first ultrasonically cleaned and then wiped by using acetone.

[0030] S12, laser etching is performed on the surface of the cleaned galvannealed aluminum magnesium steel plate 3 to prepare a surface microstructure 1, the depth of the surface microstructure 1 is less than the thickness of the plating layer on the galvannealed aluminum magnesium steel plate 3, and the etching depth of the surface microstructure 1 is 25μm; A short-pulse nanosecond laser is selected to perform laser etching on the cleaned galvannealed aluminum magnesium steel plate 3, the laser power is 50W, the scanning speed is 1500mm / s, the scanning frequency is 30KHz, the scanning times are 15, the scanning shape is set to be a linear type, mainly a groove-shaped surface microstructure, so as to ensure that the physical relaxation effect of the groove on the surface of the base material is consistent with the spread width direction of the filler metal, the groove spacing is 0.05mm, and the included angle between the groove-shaped surface microstructure and the welding direction is 90°.

[0031] S2, the galvannealed aluminum magnesium steel plate 3 with the surface microstructure 1 and the cleaned aluminum alloy plate 2 are overlapped and placed for assembly, the CMT welding machine is adjusted to appropriate process parameters, and welding is performed; The lap placement is in the following order: the galvannealed aluminum magnesium steel plate 3 is at the bottom, the aluminum alloy plate 2 is at the top, and the lap length is 10 mm. A CMT welding machine is selected as the welding source, and after the process parameters are set as follows, welding is performed: the distance between the welding gun and the workpiece is 12 mm, the welding speed is 0.3 m / min, the wire feeding speed is 4.2 min / min, the protective gas is Ar gas, and the flow rate is 15 L / min, to obtain a welded joint.

[0032] In Examples 1 and 2, by preparing the groove type surface microstructure 1 on the surface of the galvannealed aluminum magnesium steel plate 3, the behavior of the coating layer during welding is significantly optimized. The presence of the coating layer improves the fluidity and wettability of the molten pool during welding, and the Zn, Al, and Mg elements in the coating layer are more easily evaporated after laser etching, reducing the temperature of the molten pool and thus reducing the thickness of the intermetallic compound. In addition, the protective effect of the coating layer enables the welded joint to have excellent corrosion resistance during subsequent use. In contrast, if laser etching and CMT welding are directly performed on a common steel plate without a coating layer, due to the lack of lubrication and protection of the coating layer, the wettability and corrosion resistance of the welded joint are significantly reduced, and the mechanical properties cannot achieve the effect of the present application. If the same laser parameters are used to directly weld a steel plate without a coating layer, even if the same surface microstructure 1 is introduced, the tensile shear strength of the joint is only 65% (about 145 N / mm) of that of the galvannealed aluminum magnesium steel joint, and the weld area lacks coating layer protection and appears obvious corrosion within 24 hours in the salt spray test. However, by using the welding method in the present application, the strength of the welded joint can reach 272 N / mm, which fully proves the irreplaceability of the coating layer in CMT welding.

[0033] Figure 4 The macroscopic morphology diagram of the CMT connection implementation effect of the aluminum alloy and the untreated galvannealed aluminum magnesium steel in the present application; Figure 5 The macroscopic morphology diagram of the CMT connection implementation effect of the aluminum alloy and the galvannealed aluminum magnesium steel treated by laser etching in the present application can be seen Figure 5 The relaxation effect of the microstructure on the surface of the substrate is more obvious, and the addition of the microstructure reduces the resistance of the molten filler flow. The molten coating metal adheres to the weld to protect the weld. If the substrate metal is covered with a thin oxide film, the oxide surface is replaced by a clean surface of intermetallic compound through intermetallic reaction, thereby improving the wettability. It can also be found that the fracture path 6 of the joint has changed significantly, Figure 4 The fracture path 6 in the present application is approximately along the interface between the filler material and the galvannealed aluminum magnesium steel plate. Figure 5 In the present application, the fracture path is in the filler material, and this fracture mode requires more energy consumption, thus showing stronger mechanical properties.

[0034] Figure 6(a) is the contact angle topography of the CMT joint between aluminum alloy and untreated galvanized aluminum magnesium steel, from Figure 6 (b) is the contact angle topography of the CMT joint between aluminum alloy and galvanized aluminum magnesium steel after laser etching treatment, it can be observed by comparison that Figure 6 The Zn-rich region of (b) is enlarged by nearly 5 times compared with Figure 6 (a), the introduction of texture promotes the evaporation of Zn, reduces the temperature of the molten pool, but at the three-phase line, promotes the generation of zinc-aluminum compounds, which significantly reduces the wetting angle, which is all conducive to the improvement of joint performance. The tensile shear strength test of the joint is 272 N / mm, which is significantly higher than the joint strength of 183 N / mm without surface pretreatment, and the strength is improved by more than 48%.

[0035] Figure 7 (a) is the SEM effect diagram of the joint microstructure of the CMT joint between aluminum alloy and untreated galvanized aluminum magnesium steel, Figure 7 (b) is the SEM effect diagram of the joint microstructure of the CMT joint between aluminum alloy and galvanized aluminum magnesium steel after laser etching treatment. Compared with the welding on the untreated surface, the groove-shaped surface microstructure not only promotes the evaporation of Zn, reduces the temperature of the molten pool, and thins the IMC, but also increases the effective contact area of the filler metal and the base material, at the same time, promotes the expansion of the molten coating in the direction of the weld, protects the weld, and improves the interfacial bonding strength to 48% of the original surface.

[0036] The above describes the preferred embodiments of the present application. It should be understood that those skilled in the art can make many modifications and changes without creative labor according to the concept of the present application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment on the basis of the prior art according to the concept of the present application shall be within the protection scope determined by the claims.

Claims

1. A method for CMT joining of an aluminum alloy to a galvannealed aluminum magnesium steel, characterized in that, The method comprises the following steps: S1, pretreating the surfaces of the aluminum alloy plate (2) and the galvanizing aluminum magnesium steel plate (3); The pretreatment comprises the following steps: S11, performing pre-welding cleaning on the galvanizing aluminum magnesium steel plate (3) and the aluminum alloy plate (2) to be welded; S12, performing laser etching on the surface of the cleaned galvanizing aluminum magnesium steel plate (3) to prepare a surface microstructure (1), the depth of the surface microstructure (1) being less than the thickness of the plating layer on the galvanizing aluminum magnesium steel plate (3); S2, placing the galvanizing aluminum magnesium steel plate (3) with the surface microstructure (1) and the cleaned aluminum alloy plate (2) in a lap joint manner, adjusting the process parameters of a CMT welding machine, and performing welding.

2. The method for CMT dissimilar metal joining of an aluminum alloy to a galvannealed aluminum magnesium steel according to claim 1, characterized by: The aluminum alloy plate (2) contains Mg 0.9wt%, Si 0.62wt%, Fe 0.33wt%, Cu 0.28wt%, Cr 0.17wt%, Mn 0.06wt%, Zn 0.02wt%, C 0.02wt%, and the balance of Al.

3. The method for CMT dissimilar metal joining of an aluminum alloy to a galvannealed aluminum magnesium steel of claim 1, wherein: The galvanizing aluminum magnesium steel plate (3) contains Zn 15.98wt%, Al 1.15wt%, Mg 0.26wt%, Si 0.08wt%, and the balance of Fe.

4. The method for aluminum alloy and galvanizing aluminum magnesium steel CMT dissimilar metal connection according to claim 2 or 3, characterized in that: The surface microstructure (1) is a groove type surface microstructure, the depth of the groove type surface microstructure is , and the interval between the groove type surface microstructures is 0.05-0.1 mm.

5. The method for aluminum alloy and galvanizing aluminum magnesium steel CMT dissimilar metal connection according to claim 2 or 3, characterized in that: The shape of the surface microstructure (1) is a discrete dot array, or parallel grooves, or a cross grid, the depth of the surface microstructure (1) is .

6. The method for CMT dissimilar metal joining of an aluminum alloy to a galvannealed aluminum magnesium steel of claim 1, wherein: The process parameters of the laser etching in the step S12 mainly include laser power, scanning speed, scanning frequency and scanning times, the laser power is 50W, the scanning speed is 1500mm / s, the scanning frequency is 30KHz, and the scanning times are 2-10 times. times.

7. The method for CMT dissimilar metal joining of an aluminum alloy to a galvannealed aluminum magnesium steel according to claim 2 or 3, characterized in that: In the pre-welding cleaning process in step S11, the aluminum alloy plate (2) is first mechanically polished by a steel wire brush and then ultrasonically cleaned, and then wiped with acetone; the galvanizing aluminum magnesium steel plate (3) is first ultrasonically cleaned and then wiped with acetone.

8. The method for CMT dissimilar metal joining of an aluminum alloy to a galvannealed aluminum magnesium steel according to claim 2 or 3, characterized in that: In the pre-welding cleaning process in step S11, the aluminum alloy plate (2) is first mechanically polished by a steel wire brush and then ultrasonically cleaned, and then wiped with acetone; the galvanizing aluminum magnesium steel plate (3) is first ultrasonically cleaned and then wiped with acetone.

9. The method for CMT dissimilar metal joining of an aluminum alloy to a galvannealed aluminum magnesium steel of claim 1, wherein: The process parameters of the CMT welding machine in the step S2 mainly include the distance between the welding torch and the workpiece, the welding speed, the wire feeding speed and the protective gas flow rate, the distance between the welding torch and the workpiece is 10-15 mm, the welding speed is 0.5-1.5 m / min, the wire feeding speed is 1.5-2.5 m / min, and the protective gas flow rate is 10-15 L / min. m / min, the wire feeding speed m / min, and the protective gas flow rate L / min.

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