A friction stir welding method for aluminum-magnesium dissimilar alloys and the welded joint

Abstract

This invention provides a friction stir welding method for aluminum-magnesium dissimilar alloys, relating to the field of welding technology, and includes the following steps: Step 1) placing a metal transition layer between an aluminum alloy part and a magnesium alloy part; wherein, the aluminum alloy part and the metal transition layer form a first welding area, and the magnesium alloy part and the metal transition layer form a second welding area; Step 2) performing friction stir welding on the first welding area to achieve metallurgical bonding between the aluminum alloy part and the metal transition layer; performing friction stir welding on the second welding area to achieve metallurgical bonding between the magnesium alloy part and the metal transition layer. This invention achieves metallurgical bonding in aluminum-magnesium dissimilar alloy joints by adding a metal transition layer between the aluminum alloy part and the magnesium alloy part and employing double-pass friction stir welding to weld the metal transition layer to both the aluminum alloy part and the magnesium alloy part, forming intermetallic compounds at the interfaces of the aluminum alloy part-metal transition layer and the metal transition layer-magnesium alloy part respectively.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, specifically relating to a friction stir welding method and welded joint for aluminum-magnesium dissimilar alloys. Background Technology

[0002] With the escalation of global environmental problems, energy conservation and emission reduction have become a focus of international attention and action. The transportation industry, including aviation, aerospace, automotive, and shipping, is a major consumer of energy and emitter of greenhouse gases, making energy conservation and emission reduction paramount. Aluminum and magnesium alloys, with their advantages of low density and high specific strength, have become key materials for achieving lightweighting in the transportation industry. However, traditional aluminum-magnesium dissimilar alloy welding methods face numerous challenges, such as cracks, porosity, alloy element evaporation, low-temperature eutectic intermetallic compounds, and limited mutual solubility hindering the formation of a fusion zone.

[0003] Friction stir welding (FSW), as a solid-state welding technology, features low heat input and no material melting process, avoiding a series of defects inherent in traditional fusion welding. Compared to fusion welding, FSW significantly improves the mechanical properties of aluminum-magnesium dissimilar alloy joints. However, during FSW, the presence of certain low-temperature eutectic intermetallic compounds between the aluminum and magnesium materials results in a lack of metallurgical bonding between the micro-regions of the two alloys, relying solely on mechanical interlocking. This makes them prone to cracking, affecting the joint's strength and quality. Furthermore, the joint's mechanical properties are closely related to the material flow state during FSW, leading to significant fluctuations in tensile properties and poor fatigue performance.

[0004] To avoid the formation of low-temperature eutectic intermetallic compounds in aluminum-magnesium dissimilar alloy FSW joints, existing technologies involve adding thin metal sheets (less than 0.5 mm thick) of zinc, tin, copper, nickel, or steel between the aluminum and magnesium alloys to isolate them, and then welding the aluminum and magnesium using single-pass friction stir welding (single-pass FSW). However, these metal interlayers are relatively thin and easily break during the FSW process, dispersing into fragments throughout the weld. Therefore, they cannot completely isolate the eutectic reaction during the aluminum-magnesium dissimilar alloy FSW process, making it difficult to achieve metallurgical bonding in the joint and resulting in poor joint strength. Furthermore, zinc and tin, when used as metal layers, have melting points lower than the welding zone temperature, easily forming brittle compounds with the aluminum-magnesium alloy, leading to a high susceptibility to cracking in the joint. Summary of the Invention

[0005] Therefore, the present invention provides a friction stir welding method and welded joint for aluminum-magnesium dissimilar alloys, which can solve the technical problem of poor strength of aluminum-magnesium dissimilar alloy welded joints in the prior art.

[0006] To address the above problems, this invention provides a method for friction stir welding of aluminum-magnesium dissimilar alloys, comprising the following steps:

[0007] Step 1) Place the metal transition layer between the aluminum alloy part and the magnesium alloy part; wherein, the aluminum alloy part and the metal transition layer form a first area to be welded, and the magnesium alloy part and the metal transition layer form a second area to be welded.

[0008] Step 2) Perform friction stir welding on the first area to be welded to achieve metallurgical bonding between the aluminum alloy part and the metal transition layer;

[0009] Friction stir welding is performed on the second area to be welded to metallurgically bond the magnesium alloy part to the metal transition layer.

[0010] Furthermore, in step 1): the metal transition layer is a metal layer with a thickness ≥ 0.5 mm; and / or

[0011] The metal transition layer is made of a metal with a melting point higher than 660°C; preferably, the metal transition layer is made of one of pure titanium, pure nickel, pure copper, steel, titanium alloy, nickel alloy, and copper alloy; and / or

[0012] The metal transition layer is made of a metal that can form an intermetallic compound with aluminum alloy parts and magnesium alloy parts, and the formation temperature of the intermetallic compound is ≥450℃.

[0013] Furthermore, in step 1): after placing the metal transition layer between the aluminum alloy part and the magnesium alloy part, the connection method between the aluminum alloy part and the metal transition layer, and between the magnesium alloy part and the metal transition layer, is one of butt joint, lap joint, or overlap joint; and / or

[0014] In step 2): a stirring head is used for friction stir welding; the stirring head includes a shoulder and a stirring pin.

[0015] Furthermore, the aluminum alloy component is an aluminum alloy sheet; the magnesium alloy component is a magnesium alloy sheet; the aluminum alloy sheet and the magnesium alloy sheet have the same thickness direction; preferably, the aluminum alloy sheet and the magnesium alloy sheet have the same thickness; and / or

[0016] The stirring needle is cylindrical or conical in shape; and / or

[0017] The tip of the stirring needle is flat or spherical; and / or

[0018] The surface of the stirring needle is smooth, or the surface of the stirring needle has an annular groove or a thread;

[0019] The length of the stirring needle is 1–100 mm; and / or

[0020] The diameter of the root of the stirring needle is 3 to 30 mm.

[0021] Furthermore, when the connection method is butt joint or lap joint:

[0022] The thickness direction of the metal transition layer is perpendicular to the thickness direction of the aluminum alloy plate; and / or

[0023] The length of the stirring needle is 0.1–0.5 mm less than the thickness of the aluminum alloy or magnesium alloy plate; and / or

[0024] The edge of the smallest diameter part of the stirring needle is offset into the metal transition layer by 0-2 mm.

[0025] Furthermore, when the connection method is overlapping:

[0026] The thickness direction of the metal transition layer is the same as the thickness direction of the aluminum alloy plate; and / or

[0027] The difference between the length of the stirring needle and the thickness of the aluminum alloy or magnesium alloy plate is -0.2 to 0.2 mm; and / or

[0028] The distance between the end of the stirring needle and the metal transition layer is ≤0.2mm or it is inserted into the metal transition layer.

[0029] Furthermore, the stirring head is made of one of the following materials: tool steel, high-temperature alloy, tungsten alloy, or ceramic material; and / or

[0030] The diameter of the shoulder is 10–80 mm; and / or

[0031] The stirring head has a rotational speed of 25–2000 r / min, an axial pressure of 2.0–200.0 kN, and an inclination angle of 0–3°.

[0032] Furthermore, in step 2):

[0033] During friction stir welding of the first area to be welded, the aluminum alloy component is located on the retreating side of the weld; and / or

[0034] When performing friction stir welding on the second area to be welded, the magnesium alloy part is located on the back side of the weld.

[0035] Furthermore, in step 2):

[0036] The friction stir welding is one of the following: conventional friction stir welding, double-shoulder friction stir welding, differential friction stir welding, and static shoulder friction stir welding.

[0037] Preferably, the welding speed of the friction stir welding is 0.5 to 2000 mm / min.

[0038] On the other hand, the present invention provides a welded joint of aluminum-magnesium dissimilar alloy, the welded joint comprising an aluminum alloy component, a magnesium alloy component, and a metal transition layer; the aluminum alloy component and the metal transition layer are metallurgically bonded; the magnesium alloy component and the metal transition layer are metallurgically bonded.

[0039] Preferably, the tensile strength of the aluminum-magnesium dissimilar alloy welded joint is ≥180MPa, and the elongation is ≥2%.

[0040] Preferably, the welded joint is obtained by any of the above-described friction stir welding methods.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] 1. This invention provides a friction stir welding method for aluminum-magnesium dissimilar alloys, wherein a metal transition layer is placed between an aluminum alloy part and a magnesium alloy part; the aluminum alloy part and the metal transition layer form a first welding area, and the magnesium alloy part and the metal transition layer form a second welding area; then, friction stir welding is performed on the first and second welding areas respectively, so that the aluminum alloy part and the metal transition layer are metallurgically bonded, and the magnesium alloy part and the metal transition layer are metallurgically bonded between the aluminum alloy part and the magnesium alloy part; based on the above method, this invention adds a metal transition layer between the aluminum alloy part and the magnesium alloy part, and uses double-pass friction stir welding (FSW) to weld the metal transition layer to the aluminum alloy and the magnesium alloy respectively, forming intermetallic compounds at the two interfaces of aluminum alloy part-metal transition layer and metal transition layer-magnesium alloy part, thereby achieving metallurgical connection in the aluminum-magnesium dissimilar alloy joint, effectively improving the joint strength and welding quality stability.

[0043] 2. Furthermore, the present invention uses a metal with a thickness of ≥0.5mm as the metal transition layer, which can prevent the metal transition layer from breaking into fragments and distributing in the weld during the FSW process. Therefore, it can effectively isolate the eutectic reaction during the FSW process of aluminum-magnesium dissimilar alloys and ensure the mechanical properties of the joint. In addition, selecting a metal with a melting point higher than 660℃ as the metal transition layer can prevent it from forming brittle compounds with magnesium alloys or aluminum alloys.

[0044] 3. On the other hand, the present invention provides an aluminum-magnesium dissimilar alloy welded joint, which is obtained by the above-mentioned friction stir welding method. The aluminum-magnesium dissimilar alloy welded joint includes an aluminum alloy part, a magnesium alloy part, and a metal transition layer; wherein, the aluminum alloy part is metallurgically bonded to the metal transition layer, and the magnesium alloy part is metallurgically bonded to the metal transition layer, and the metallurgical bonding phase is a high-melting-point intermetallic compound (such as FeAl2, Fe2Al5, FeAl3, Fe3Al, FeAl amorphous, Al2Cu, Al3Cu, Ti3Al, TiAl, TiAl3, AlNi3, etc.); therefore, the aluminum-magnesium dissimilar alloy welded joint of the present invention has high strength (tensile strength ≥180MPa), and there is no low-melting-point eutectic phase in the joint. Attached Figure Description

[0045] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0046] Figure 1 This is a flowchart of the friction stir welding method of the present invention; wherein, (a) is a butt joint and (b) is an lap joint.

[0047] Figure 2 These are microstructure diagrams of the aluminum-magnesium dissimilar alloy welded joint according to Embodiment 1 of the present invention; wherein, (a) is a cross-sectional macroscopic morphology diagram, (b) is a microstructure diagram of the interface between the magnesium alloy plate and the metal transition layer, and (c) is a microstructure diagram of the interface between the aluminum alloy plate and the metal transition layer.

[0048] Figure 3 These are the tensile curves of aluminum-magnesium dissimilar alloy welded joints in the embodiments and comparative examples of the present invention; wherein, 1 is the tensile curve of the aluminum-magnesium dissimilar alloy welded joint of Example 1, 2 is the tensile curve of the aluminum-magnesium dissimilar alloy welded joint of Example 2, 3 is the tensile curve of the aluminum-magnesium dissimilar alloy welded joint of Comparative Example 1, and 4 is the tensile curve of the aluminum-magnesium dissimilar alloy welded joint of Comparative Example 2.

[0049] Figure 4 These are microstructure diagrams of the aluminum-magnesium dissimilar alloy welded joint according to Embodiment 2 of the present invention; wherein, (a) is a cross-sectional macroscopic morphology diagram, (b) is a microstructure diagram of the interface between the magnesium alloy plate and the metal sandwich layer, and (c) is a microstructure diagram of the interface between the aluminum alloy plate and the metal sandwich layer.

[0050] Figure 5 These are morphological images of the aluminum-magnesium dissimilar alloy welded joint of Comparative Example 1 of the present invention; wherein, (a) is the macroscopic morphology of the cross section, and (b) is the microscopic morphology of the weld.

[0051] Figure 6 These are morphological images of the aluminum-magnesium dissimilar alloy welded joint of Comparative Example 2 of the present invention; wherein, (a) is the macroscopic morphology of the cross section, (b) is the distribution pattern of metal interlayer fragments in the weld, and (c) is an enlarged view of the hole defects in the weld.

[0052] The attached figures are labeled as follows:

[0053] 1-Welding pad, 2-Aluminum alloy plate, 3-Magnesium alloy plate, 4-Metal transition layer, 5-Stirring head, 6-Weld. Detailed Implementation

[0054] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0055] This invention provides a method for friction stir welding of aluminum-magnesium dissimilar alloys, such as... Figure 1 As shown, it includes the following steps:

[0056] Step 1) Place the metal transition layer between the aluminum alloy part and the magnesium alloy part; wherein, the aluminum alloy part and the metal transition layer form a first area to be welded, and the magnesium alloy part and the metal transition layer form a second area to be welded.

[0057] Step 2) Perform friction stir welding on the first area to be welded to achieve metallurgical bonding between the aluminum alloy part and the metal transition layer; perform friction stir welding on the second area to be welded to achieve metallurgical bonding between the magnesium alloy part and the metal transition layer; wherein, the welding speed of friction stir welding is 0.5~2000mm / min.

[0058] Based on the above method, this invention adds a metal transition layer between aluminum alloy and magnesium alloy parts, and then uses double-pass friction stir welding (FSW) to weld the metal transition layer to both the aluminum alloy and magnesium alloy parts. Intermetallic compounds are formed at both the aluminum alloy part-metal transition layer and metal transition layer-magnesium alloy parts interfaces, thereby achieving metallurgical connection in aluminum-magnesium dissimilar alloy joints and effectively improving joint strength and weld quality stability. The friction stir welding method of this invention is simple and easy to implement, suitable for automated and large-scale production.

[0059] In some embodiments, the metal transition layer is a metal layer with a thickness ≥ 0.5 mm; the metal transition layer uses a metal with a melting point higher than 660°C; preferably, the metal transition layer uses one of pure titanium, pure nickel, pure copper, steel, titanium alloy, nickel alloy, and copper alloy; the metal transition layer uses a metal that can form an intermetallic compound with aluminum alloy parts or magnesium alloy parts, and the formation temperature of the intermetallic compound is ≥ 450°C; when the formation temperature of the intermetallic compound is ≥ 450°C, its strengthening effect is better.

[0060] In some embodiments, in step 1), after the metal transition layer is placed between the aluminum alloy part and the magnesium alloy part, the connection method between the aluminum alloy part and the metal transition layer, and between the magnesium alloy part and the metal transition layer, is one of butt joint, lap joint, or overlap joint.

[0061] In step 2): the friction stir welding adopts one of the following: conventional friction stir welding, double-shoulder friction stir welding, differential friction stir welding, and static shoulder friction stir welding; a stirring head is used for friction stir welding; the stirring head includes a shoulder and a stirring pin;

[0062] The stirring head is made of one of the following materials: tool steel, high-temperature alloy, tungsten alloy, or ceramic material; the shoulder diameter is 10–80 mm; the root diameter of the stirring pin is 3–30 mm; the length of the stirring pin is 1–100 mm; the shape of the stirring pin is cylindrical or conical; the end of the stirring pin is flat or spherical; the surface of the stirring pin is smooth, or the surface of the stirring pin has an annular groove or thread; the side of the stirring pin may or may not be machined with a side plane; the rotation speed of the stirring head is 25–2000 r / min; the axial pressure is 2.0–200.0 kN; and the tilt angle of the stirring head is 0–3°.

[0063] In some embodiments, the aluminum alloy part is an aluminum alloy plate; the magnesium alloy part is a magnesium alloy plate; the aluminum alloy plate and the magnesium alloy plate have the same thickness direction; preferably, the aluminum alloy plate and the magnesium alloy plate have the same thickness.

[0064] When the connection method is butt joint or lap joint: the thickness direction of the metal transition layer is perpendicular to the thickness direction of the aluminum alloy plate; the needle length of the stirring needle is 0.1 to 0.5 mm smaller than the thickness of the aluminum alloy plate or magnesium alloy plate; the edge of the part with the smallest diameter of the stirring needle is offset into the metal transition layer by 0 to 2 mm towards the advancing side of the weld.

[0065] When the connection method is lap joint: the thickness direction of the metal transition layer is the same as the thickness direction of the aluminum alloy plate; the difference between the length of the stirring needle and the thickness of the aluminum alloy plate or magnesium alloy plate is -0.2 to 0.2 mm; the distance between the end of the stirring needle and the metal transition layer is ≤0.2 mm or it is inserted into the metal transition layer.

[0066] When performing friction stir welding on the first area to be welded, the aluminum alloy component is located on the retreating side of the weld; when performing friction stir welding on the second area to be welded, the magnesium alloy component is located on the retreating side of the weld; this helps to avoid defects. Simultaneously, before performing friction stir welding, the oxide film on the surfaces of the aluminum alloy component, magnesium alloy component, and metal transition layer to be in contact is removed, and the surfaces are cleaned.

[0067] On the other hand, the present invention provides a welded joint of aluminum-magnesium dissimilar alloy, the welded joint comprising an aluminum alloy part, a magnesium alloy part and a metal transition layer; the aluminum alloy part and the metal transition layer are metallurgically bonded; the magnesium alloy part and the metal transition layer are metallurgically bonded.

[0068] Preferably, the tensile strength of the aluminum-magnesium dissimilar alloy welded joint is ≥180MPa, and the elongation is ≥2%.

[0069] Preferably, the welded joint is obtained by any of the above-mentioned friction stir welding methods.

[0070] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0071] Example 1

[0072] See Figure 1 This embodiment provides a method for friction stir welding of aluminum-magnesium dissimilar alloys, including the following steps:

[0073] Step 1) Place the metal transition layer between the aluminum alloy plate and the magnesium alloy plate; wherein, the aluminum alloy plate and the metal transition layer form the first area to be welded, and the magnesium alloy plate and the metal transition layer form the second area to be welded.

[0074] The aluminum alloy plate is a 3mm thick 6061-T6 rolled aluminum alloy sheet, and the magnesium alloy plate is a 3mm thick ZK60 rolled magnesium alloy sheet. Q235 steel plate is used as the metal transition layer, with a thickness of 3mm and a width of 3mm. In addition, before step 1), the surface oxide film on the upper and lower surfaces and mating surfaces of the aluminum alloy plate, magnesium alloy plate, and metal transition layer is mechanically ground, and the oil stains on the surfaces to be in contact are cleaned with a dry cloth dipped in acetone or ethanol. The aluminum alloy plate is mated with the metal transition layer, and the magnesium alloy plate is mated with the metal transition layer.

[0075] Step 2) Use a stirring head to perform friction stir welding on the first area to be welded, and then use a stirring head to perform friction stir welding on the second area to be welded to obtain an aluminum-magnesium dissimilar alloy welded joint.

[0076] The stirring head includes a shoulder and a stirring pin. The stirring head is made of H13 steel. The shoulder is concave and has a diameter of 16mm. The stirring pin is cylindrical and has a right-hand thread on its surface. The diameter of the stirring pin is 6mm and the length of the stirring pin is 2.8mm. The edge of the stirring pin is offset into the Q235 steel on the weld seam advance side by 0.2mm.

[0077] During friction stir welding, both the aluminum alloy plate and the magnesium alloy plate are located on the retreating side of the weld. The welding process parameters are: rotation speed of 800 rpm and welding speed of 50 mm / min.

[0078] Example 1 utilizes the fact that both aluminum-steel and magnesium-steel can form good bonds, transforming the connection between aluminum-magnesium dissimilar alloys into a connection between aluminum-steel-magnesium alloys, effectively avoiding the aluminum-magnesium eutectic reaction. The microstructure of the aluminum-magnesium dissimilar alloy welded joint obtained by the friction stir welding method of this example is as follows: Figure 2 As shown, no welding defects were found in the joint, and the interface bonding between the aluminum alloy plate and the metal transition layer, as well as between the magnesium alloy plate and the metal transition layer, is good; Figure 3 As shown in curve 1, the tensile strength of the aluminum-magnesium dissimilar alloy welded joint was measured to be 199 MPa, and the elongation was 3.2%.

[0079] Example 2

[0080] See Figure 1 This embodiment provides a method for friction stir welding of aluminum-magnesium dissimilar alloys, including the following steps:

[0081] Step 1) Place the metal transition layer between the aluminum alloy plate and the magnesium alloy plate; wherein, the aluminum alloy plate and the metal transition layer form the first area to be welded, and the magnesium alloy plate and the metal transition layer form the second area to be welded.

[0082] The aluminum alloy plate is a 3mm thick 6061-T6 rolled aluminum alloy sheet, and the magnesium alloy plate is a 3mm thick ZK60 rolled magnesium alloy sheet. Q235 steel plate is used as the metal transition layer, with a thickness of 3mm and a width of 4mm. In addition, before step 1), the surface oxide film on the upper and lower surfaces and mating surfaces of the aluminum alloy plate, magnesium alloy plate, and metal transition layer is mechanically ground, and the oil stains on the surfaces to be in contact are cleaned with a dry cloth dipped in acetone or ethanol. The aluminum alloy plate and the metal transition layer are mated together, and the magnesium alloy plate and the metal transition layer are mated together.

[0083] Step 2) First, friction stir welding is performed on the first area to be welded, and then friction stir welding is performed on the second area to be welded using a stirring head to obtain an aluminum-magnesium dissimilar alloy welded joint.

[0084] The stirring head includes a shoulder and a stirring pin. The stirring head is made of H13 steel. The shoulder is concave and has a diameter of 16mm. The stirring pin is cylindrical and has a right-hand thread on its surface. The diameter of the stirring pin is 6mm and the length of the stirring pin is 2.8mm. The edge of the stirring pin is offset 0.5mm into the Q235 steel on the weld seam advance side.

[0085] During friction stir welding, both the aluminum alloy plate and the magnesium alloy plate are located on the retreating side of the weld. The welding process parameters are: rotation speed of 2000 rpm and welding speed of 100 mm / min.

[0086] Example 2 utilizes the fact that both aluminum-steel and magnesium-steel can form good bonds, transforming the connection between aluminum-magnesium dissimilar alloys into a connection between aluminum-steel-magnesium alloys, effectively avoiding the aluminum-magnesium eutectic reaction. The microstructure of the aluminum-magnesium dissimilar alloy welded joint obtained by the friction stir welding method of this example is as follows: Figure 4 As shown, no welding defects were found in the joint, and the interface bonding between the aluminum alloy plate and the metal transition layer, as well as between the magnesium alloy plate and the metal transition layer, is good; Figure 3 As shown in curve 2, the tensile strength of the aluminum-magnesium dissimilar alloy welded joint was measured to be 206 MPa and the elongation was 3.7%.

[0087] Comparative Example 1

[0088] This comparative example provides a method for friction stir welding of aluminum-magnesium dissimilar alloys, including the following steps:

[0089] Step 1) Butt the aluminum alloy plate and the magnesium alloy plate together;

[0090] The aluminum alloy plate is a 3mm thick 6061-T6 aluminum alloy rolled plate, and the magnesium alloy plate is a 3mm thick ZK60 magnesium alloy rolled plate. In addition, before the connection, the oxide film on the surfaces of the aluminum alloy plate and the magnesium alloy plate to be in contact is mechanically ground, and the oil stains on the surfaces to be in contact are cleaned with a dry cloth dipped in acetone or ethanol.

[0091] Step 2) Use a stirring head to perform friction stir welding on the butt joint of the aluminum alloy plate and the magnesium alloy plate to obtain an aluminum-magnesium dissimilar alloy welded joint.

[0092] The stirring head includes a shoulder and a stirring pin. The stirring head is made of H13 steel, the shoulder is concave with a diameter of 16mm, the stirring pin is cylindrical with a right-hand thread on its surface, a diameter of 6mm, and a pin length of 2.8mm. The aluminum alloy plate is located on the retreating side of the weld. The edge of the stirring pin is offset 0.2mm into the magnesium alloy plate on the advancing side of the weld.

[0093] During friction stir welding, the aluminum alloy plate is located on the retreating side of the weld, and the magnesium alloy plate is located on the advancing side of the weld. The welding process parameters are: rotation speed 800 rpm and welding speed 50 mm / min.

[0094] Compared to the examples, this comparative example did not add a metal transition layer between the aluminum-magnesium dissimilar alloy plates, and the resulting welded joint microstructure is as follows: Figure 5 As shown, obvious hole defects can be found in the joint. Figure 5 a) This is mainly due to the fact that during the welding process, the aluminum-magnesium alloy mixes together and undergoes a eutectic reaction, resulting in the formation of a large amount of low-melting-point aluminum-magnesium eutectic compounds at the aluminum-magnesium interface. Figure 5 b) These aluminum-magnesium intermetallic compounds have a melting point below 450°C and a weld center temperature exceeding 500°C. Being in a liquid state, these compounds prevent welding tools from effectively driving material flow, resulting in voids and defects in the weld. Figure 3 As shown in curve 3, the tensile strength of the aluminum-magnesium dissimilar alloy welded joint was measured to be 125 MPa and the elongation was 1.2%.

[0095] Comparative Example 2

[0096] This comparative example provides a method for friction stir welding of aluminum-magnesium dissimilar alloys, including the following steps:

[0097] Step 1) Place the metal interlayer between the aluminum alloy plate and the magnesium alloy plate; wherein the aluminum alloy plate is butted with the metal interlayer, and the magnesium alloy plate is butted with the metal interlayer.

[0098] The aluminum alloy plate is a 3mm thick 6061-T6 aluminum alloy rolled plate, and the magnesium alloy plate is a 3mm thick ZK60 magnesium alloy rolled plate; pure iron sheet is used as the metal interlayer, with a thickness of 0.1mm and a width of 3mm; in addition, before step 1), the surface oxide film on the upper and lower surfaces and mating surfaces of the aluminum alloy plate, magnesium alloy plate and metal interlayer is mechanically ground, and the oil stains on the surfaces to be in contact are cleaned with a dry cloth dipped in acetone or ethanol.

[0099] Step 2) Use a stirring head to perform single-pass friction stir welding at the butt joint to weld the aluminum alloy plate and the magnesium alloy plate together to obtain an aluminum-magnesium dissimilar alloy welded joint.

[0100] The stirring head includes a shoulder and a stirring pin. The stirring head is made of H13 steel. The shoulder is concave and has a diameter of 16mm. The stirring pin is cylindrical and has a right-hand thread on its surface. The diameter of the stirring pin is 6mm and the length of the stirring pin is 2.8mm. The edge of the stirring pin is offset into the ZK60 magnesium alloy on the weld seam advance side by 0.5mm.

[0101] During friction stir welding, the aluminum alloy plate is located on the retreating side of the weld, and the magnesium alloy plate is located on the advancing side of the weld. The welding process parameters are: rotation speed of 800 rpm and welding speed of 50 mm / min.

[0102] Compared to the examples, this comparative example adds a metal interlayer (pure iron sheet) between aluminum-magnesium dissimilar alloy plates, and the microstructure of the welded joint obtained by single-pass FSW is as follows. Figure 6 As shown, it can be observed that the metal interlayer in the weld is broken into small fragments, thus failing to completely isolate the aluminum-magnesium eutectic reaction. Because the metal interlayer fragments interfere with the material flow during friction stir welding, welding defects exist in the weld. Figure 3 As shown in curve 4, the tensile strength of the aluminum-magnesium dissimilar alloy welded joint was measured to be 150 MPa and the elongation was 1%.

[0103] It will be readily understood by those skilled in the art that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the protection scope of the present invention.

Claims

1. A friction stir welding method of an aluminum magnesium dissimilar alloy, characterized by, The method comprises the following steps: Step 1) placing a metal adapter layer between an aluminum alloy piece and a magnesium alloy piece; wherein the aluminum alloy piece and the metal adapter layer form a first to-be-welded area, and the magnesium alloy piece and the metal adapter layer form a second to-be-welded area; wherein the metal adapter layer is a metal layer with a thickness of ≥0.5 mm; the metal adapter layer is made of a metal with a melting point higher than 660℃; Step 2) performing friction stir welding on the first to-be-welded area to make the aluminum alloy piece and the metal adapter layer metallurgically bonded; wherein intermetallic compounds are formed at the interface between the aluminum alloy piece and the metal adapter layer; performing friction stir welding on the second to-be-welded area to make the magnesium alloy piece and the metal adapter layer metallurgically bonded; wherein intermetallic compounds are formed at the interface between the metal adapter layer and the magnesium alloy piece.

2. The friction stir welding method of dissimilar aluminum magnesium alloys according to claim 1, characterized by, In the step 1): the metal adapter layer is made of one of pure titanium, pure nickel, pure copper, steel, titanium alloy, nickel alloy, and copper alloy; and / or the metal adapter layer is made of a metal that can form intermetallic compounds with the aluminum alloy piece and the magnesium alloy piece, and the formation temperature of the intermetallic compounds is ≥450℃.

3. The friction stir welding method of dissimilar aluminum magnesium alloys according to claim 1, characterized by, In the step 1): after placing the metal adapter layer between the aluminum alloy piece and the magnesium alloy piece, the connection mode between the aluminum alloy piece and the metal adapter layer and between the magnesium alloy piece and the metal adapter layer is one of butt joint, butt lap joint, and lap joint; and / or In the step 2): a stirring head is used for friction stir welding; the stirring head comprises a shoulder and a stirring pin.

4. The friction stir welding method of dissimilar aluminum magnesium alloys according to claim 3, characterized by, The aluminum alloy piece is an aluminum alloy plate; the magnesium alloy piece is a magnesium alloy plate; the thickness direction of the aluminum alloy plate is the same as that of the magnesium alloy plate; the thickness of the aluminum alloy plate is the same as that of the magnesium alloy plate; and / or the shape of the stirring pin is a cylinder or a cone; and / or the end of the stirring pin is a flat surface or a spherical surface; and / or the surface of the stirring pin is smooth, or the surface of the stirring pin has an annular groove or a thread; the length of the stirring pin is 1-100 mm; and / or the root diameter of the stirring pin is 3-30 mm.

5. The friction stir welding method of dissimilar aluminum magnesium alloys according to claim 4, characterized by, When the connection mode is butt joint or butt lap joint: the thickness direction of the metal adapter layer is perpendicular to the thickness direction of the aluminum alloy plate; and / or the length of the stirring pin is 0.1-0.5 mm smaller than the thickness of the aluminum alloy plate or the magnesium alloy plate; and / or the edge of the part with the smallest diameter of the stirring pin is offset into the metal adapter layer by 0-2 mm.

6. The friction stir welding method of dissimilar aluminum magnesium alloys of claim 4, wherein When the connection mode is lap joint: the thickness direction of the metal adapter layer is the same as the thickness direction of the aluminum alloy plate; and / or the difference between the length of the stirring pin and the thickness of the aluminum alloy plate or the magnesium alloy plate is -0.2-0.2 mm; and / or the distance between the end of the stirring pin and the metal adapter layer is ≤0.2 mm or the stirring pin is inserted into the metal adapter layer.

7. The friction stir welding method of dissimilar aluminum magnesium alloys of claim 3, wherein The material of the stirring head is one of tool steel, high-temperature alloy, tungsten alloy, and ceramic material; and / or the diameter of the shoulder is 10-80 mm; and / or the rotation speed of the stirring head is 25-2000 r / min; the axial pressure is 2.0-200.0 kN, and the inclination angle of the stirring head is 0-3°.

8. The friction stir welding method of dissimilar aluminum magnesium alloys of claim 1, wherein In the step 2): In the step of friction stir welding the first region to be welded, the aluminum alloy piece is located at the trailing side of the weld; and / or In the step of friction stir welding the second region to be welded, the magnesium alloy piece is located at the trailing side of the weld.

9. The friction stir welding method of dissimilar aluminum magnesium alloys as claimed in claim 1, wherein, In the step 2): The friction stir welding is one of conventional friction stir welding, dual-shoulder friction stir welding, differential speed friction stir welding and static shoulder friction stir welding.

10. The friction stir welding method of dissimilar aluminum magnesium alloys of claim 1, wherein The welding speed of the friction stir welding is 0.5-2000 mm / min.

11. An aluminum-magnesium dissimilar alloy welded joint, characterized by, The aluminum-magnesium dissimilar alloy welded joint comprises an aluminum alloy piece, a magnesium alloy piece and a metal transition layer; the aluminum alloy piece is metallurgically combined with the metal transition layer; the magnesium alloy piece is metallurgically combined with the metal transition layer. The tensile strength of the aluminum-magnesium dissimilar alloy welded joint is ≥180 MPa, and the elongation is ≥2%. The aluminum-magnesium dissimilar alloy welded joint is obtained by the friction stir welding method according to any one of claims 1-10.

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