Friction stir welding method for aluminum-magnesium dissimilar alloy and welding joint

Abstract

The invention provides a friction stir welding method for aluminum-magnesium dissimilar alloy, which relates to the technical field of welding and comprises the following steps: step 1) placing a metal transfer layer between an aluminum alloy part and a magnesium alloy part; wherein the aluminum alloy part and the metal transfer layer form a first to-be-welded area, and a second to-be-welded area is formed between the magnesium alloy part and the metal transfer layer; (2) friction stir welding is conducted on the first to-be-welded area, so that the aluminum alloy part and the metal transfer layer are metallurgically bonded; and the second to-be-welded area is subjected to friction stir welding, so that the magnesium alloy part and the metal transfer layer are metallurgically bonded. According to the method, the metal transfer layer is added between the aluminum alloy part and the magnesium alloy part, the metal transfer layer is welded to the aluminum alloy part and the magnesium alloy part through double-pass friction stir welding, and intermetallic compounds are formed on the two interfaces of the aluminum alloy part-metal transfer layer and the metal transfer layer-magnesium alloy part respectively; and therefore, metallurgical connection is realized in the aluminum-magnesium dissimilar alloy joint.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a friction stir welding method and a welding joint of aluminum-magnesium dissimilar alloys. Background Art

[0002] As global environmental problems intensify, energy conservation and emission reduction have become the focus of widespread concern and action by the international community. As one of the important areas of energy consumption and greenhouse gas emissions, the transportation industry, such as aviation, aerospace, automobiles, and ships, is of great urgency and importance in energy conservation and emission reduction. Aluminum alloys and magnesium alloys have the advantages of low density and high specific strength, making them key materials for lightweighting in the transportation industry. However, the traditional aluminum-magnesium dissimilar alloy fusion welding method has many challenges, such as cracks, pores, evaporation of alloy elements, low-temperature eutectic intermetallic compounds, and difficulty in forming a fusion zone due to limited mutual solubility.

[0003] Friction stir welding (FSW) is a solid-state welding technology with low heat input and no material melting process, which avoids a series of defects in traditional fusion welding. Compared with fusion welding, the use of FSW to weld aluminum-magnesium dissimilar alloys can significantly improve the mechanical properties of aluminum-magnesium dissimilar alloy joints. However, when using FSW, since there is still a certain amount of low-temperature eutectic intermetallic compounds between the two materials of aluminum and magnesium, there is no metallurgical bonding between the micro-regions of the two alloys of aluminum and magnesium, and they are only connected together by mechanical interlocking, so cracks are easily formed, affecting the strength and quality of the joint; in addition, the mechanical properties of the joint are closely related to the flow state of the material during the FSW process, so the tensile properties of the joint fluctuate greatly and the fatigue properties are very poor.

[0004] In order to avoid the formation of low-temperature eutectic intermetallic compounds in the FSW joint of aluminum-magnesium dissimilar alloys, existing technologies have added thin metal sheets (thickness less than 0.5mm) such as zinc, tin, copper, nickel, and steel between aluminum-magnesium alloys to isolate the aluminum-magnesium alloys, and achieve aluminum-magnesium welding through single-pass friction stir welding (single-pass FSW). However, these metal interlayers are relatively thin and are easily broken during the FSW process. After becoming fragments, they are distributed in the weld, so the eutectic reaction during the FSW process of aluminum-magnesium dissimilar alloys cannot be completely isolated, making it difficult to achieve metallurgical bonding in the FSW joint of aluminum-magnesium dissimilar alloys, resulting in poor joint strength; at the same time, when zinc and tin are used as metal layers, their melting points are lower than the temperature of the welding zone, and they are easy to form brittle compounds with aluminum-magnesium alloys, causing the joint to be prone to cracks. Summary of the invention

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

[0006] In order to solve the above problems, the present invention provides a friction stir welding method for aluminum-magnesium dissimilar alloys, comprising the following steps:

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

[0008] Step 2) performing friction stir welding on the first area to be welded to metallurgically bond the aluminum alloy part to the metal transfer layer;

[0009] Stir friction welding is performed on the second area to be welded to metallurgically bond the magnesium alloy part to the metal transfer layer.

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

[0011] The metal transfer layer is made of a metal with a melting point higher than 660° C.; preferably, the metal transfer 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 transfer layer is made of a metal that can form an intermetallic compound with an aluminum alloy part or a magnesium alloy part, and the formation temperature of the intermetallic compound is ≥450°C.

[0013] Furthermore, in the step 1), after the metal transfer layer is placed between the aluminum alloy part and the magnesium alloy part, the connection between the aluminum alloy part and the metal transfer layer, and between the magnesium alloy part and the metal transfer layer are all one of butt joint, butt overlap, and overlap; and / or

[0014] In the step 2), a stirring head is used to perform friction stir welding; the stirring head comprises a shaft shoulder and a stirring needle.

[0015] Further, the aluminum alloy part is an aluminum alloy plate; the magnesium alloy part is a magnesium alloy plate; the thickness direction of the aluminum alloy plate and the magnesium alloy plate is the same; preferably, the thickness of the aluminum alloy plate and the magnesium alloy plate is the same; and / or

[0016] The stirring needle has a cylindrical or conical shape; and / or

[0017] The end 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 to 100 mm; and / or

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

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

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

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

[0024] The edge of the stirring needle at the smallest diameter portion deviates into the metal transfer layer by 0 to 2 mm.

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

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

[0027] The difference between the needle length of the stirring needle and the thickness of the aluminum alloy plate or the 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 transfer layer is ≤0.2 mm or the stirring needle is inserted into the metal transfer layer.

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

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

[0031] 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°.

[0032] Further, in the step 2):

[0033] When the first area to be welded is subjected to friction stir welding, the aluminum alloy part is located at the retreat side of the weld; and / or

[0034] When the second area to be welded is subjected to friction stir welding, the magnesium alloy part is located at the retreat side of the weld.

[0035] Further, in the step 2):

[0036] The friction stir welding adopts one of 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 alloys, the welded joint comprising an aluminum alloy part, a magnesium alloy part and a metal transition layer; the aluminum alloy part is metallurgically bonded to the metal transition layer; the magnesium alloy part is metallurgically bonded to the metal transition layer;

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

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

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

[0042] 1. The present invention provides a stir friction welding method for aluminum-magnesium dissimilar alloys, wherein a metal transfer layer is placed between an aluminum alloy part and a magnesium alloy part; the aluminum alloy part and the metal transfer layer form a first area to be welded, and a second area to be welded is formed between the magnesium alloy part and the metal transfer layer; then the first area to be welded and the second area to be welded are respectively subjected to stir friction welding to metallurgically bond the aluminum alloy part to the metal transfer layer, and the magnesium alloy part to the metal transfer layer by metallurgically bonding between the aluminum alloy part and the magnesium alloy part; based on the above method, the present invention adds a metal transfer layer between the aluminum alloy part and the magnesium alloy part, and adopts double-pass stir friction welding (FSW) to weld the metal transfer layer to the aluminum alloy and the magnesium alloy respectively, and forms intermetallic compounds at the two interfaces of the aluminum alloy part-metal transfer layer and the metal transfer layer-magnesium alloy part, thereby realizing metallurgical connection in the aluminum-magnesium dissimilar alloy joint, and effectively improving the joint strength and welding quality stability.

[0043] 2. Furthermore, the present invention uses a metal with a thickness of ≥0.5 mm as the metal transition layer, which can prevent the metal transition layer from breaking into fragments and distributing them in the weld during the FSW process. Therefore, the eutectic reaction during the FSW process of the aluminum-magnesium dissimilar alloy can be effectively isolated to ensure the mechanical properties of the joint; in addition, a metal with a melting point higher than 660°C is selected as the metal transition layer to prevent it from forming a brittle compound with the magnesium alloy or the aluminum alloy.

[0044] 3. On the other hand, the present invention provides an aluminum-magnesium dissimilar alloy weld joint, which is obtained by the above-mentioned stir friction welding method, and the aluminum-magnesium dissimilar alloy weld joint comprises 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, 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 weld joint of the present invention has high strength (tensile strength ≥180MPa), and there is no low melting point eutectic phase in the joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0046] Figure 1 Flow chart of the friction stir welding method of the present invention; wherein (a) is a butt joint method, and (b) is an overlap method;

[0047] Figure 2 1 is a microstructure diagram of the aluminum-magnesium dissimilar alloy weld joint of Example 1 of the present invention; wherein (a) is a cross-sectional macroscopic morphology diagram, (b) is an interface microstructure diagram of the magnesium alloy plate / metal transition layer, and (c) is an interface microstructure diagram of the aluminum alloy plate / metal transition layer;

[0048] Figure 3 1 is the tensile curve of the aluminum-magnesium dissimilar alloy welded joint of the embodiment of the present invention and the comparative example; wherein 1 is the tensile curve of the aluminum-magnesium dissimilar alloy welded joint of embodiment 1, 2 is the tensile curve of the aluminum-magnesium dissimilar alloy welded joint of embodiment 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 1 is a microstructure diagram of the aluminum-magnesium dissimilar alloy welded joint of Example 2 of the present invention; wherein (a) is a cross-sectional macroscopic morphology diagram, (b) is a microstructure diagram of the interface of the magnesium alloy plate / metal interlayer, and (c) is a microstructure diagram of the interface of the aluminum alloy plate / metal interlayer;

[0050] Figure 5 1 is a morphology diagram of an aluminum-magnesium dissimilar alloy weld joint of Comparative Example 1 of the present invention; wherein (a) is a cross-sectional macroscopic morphology, and (b) is a weld microscopic morphology;

[0051] Figure 6 3 is a morphology diagram 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 morphology of the metal interlayer fragments in the weld, and (c) is an enlarged diagram of the hole defect in the weld;

[0052] The accompanying drawings are marked as follows:

[0053] 1- welding pad, 2- aluminum alloy plate, 3- magnesium alloy plate, 4- metal transfer layer, 5- stirring head, 6- weld seam. DETAILED DESCRIPTION

[0054] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. The drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0055] The present invention provides a friction stir welding method for aluminum-magnesium dissimilar alloys, such as Figure 1 As shown, the following steps are included:

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

[0057] Step 2) Stir friction welding is performed on the first area to be welded to metallurgically bond the aluminum alloy part to the metal transfer layer; stir friction welding is performed on the second area to be welded to metallurgically bond the magnesium alloy part to the metal transfer layer; wherein the welding speed of the stir friction welding is 0.5 to 2000 mm / min.

[0058] Based on the above method, the present invention adds a metal transfer layer between the aluminum alloy part and the magnesium alloy part, and uses double-pass friction stir welding (FSW) to weld the metal transfer layer to the aluminum alloy and the magnesium alloy respectively, and forms intermetallic compounds at the two interfaces of the aluminum alloy part-metal transfer layer and the metal transfer layer-magnesium alloy part, thereby realizing metallurgical connection in the aluminum-magnesium dissimilar alloy joint, effectively improving the joint strength and welding quality stability. The friction stir welding method of the present invention is simple and easy to operate, and is suitable for automated and large-scale production.

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

[0060] In some embodiments, in step 1), after the metal transfer layer is placed between the aluminum alloy part and the magnesium alloy part, the connection between the aluminum alloy part and the metal transfer layer, and between the magnesium alloy part and the metal transfer layer are both one of butt joint, overlap joint, and overlap joint;

[0061] In step 2), the friction stir welding adopts one of conventional friction stir welding, double-shoulder friction stir welding, differential friction stir welding, and static shoulder friction stir welding; the friction stir welding is performed using a stirring head; the stirring head includes a shoulder and a stirring needle;

[0062] Among them, the material of the stirring head is one of tool steel, high-temperature alloy, tungsten alloy, and ceramic material; the shoulder diameter is 10 to 80 mm; the root diameter of the stirring needle is 3 to 30 mm; the length of the stirring needle is 1 to 100 mm; the shape of the stirring needle is cylindrical or conical; the end of the stirring needle is flat or spherical; the surface of the stirring needle is smooth, or the surface of the stirring needle has annular grooves or threads; the side surface of the stirring needle is machined or not machined; the rotation speed of the stirring head is 25 to 2000 r / min; the axial pressure is 2.0 to 200.0 kN, and the inclination angle of the stirring head is 0 to 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 butt overlap: the thickness direction of the metal transfer layer is perpendicular to the thickness direction of the aluminum alloy plate; the needle length of the stirring needle is 0.1-0.5mm 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 deviates 0-2mm into the metal transfer layer toward the advancing side of the weld;

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

[0066] When friction stir welding is performed on the first area to be welded, the aluminum alloy part is located on the retreat side of the weld; when friction stir welding is performed on the second area to be welded, the magnesium alloy part is located on the retreat side of the weld; this is conducive to avoiding defects. At the same time, before friction stir welding, the oxide film on the contact surface of the aluminum alloy part, the magnesium alloy part and the metal transfer layer is removed and the surface is cleaned.

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

[0068] Preferably, the tensile strength of the aluminum-magnesium dissimilar alloy weld 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 is further described below with reference to specific embodiments and comparative examples.

[0071] Example 1

[0072] See also Figure 1 The present embodiment provides a friction stir welding method for aluminum-magnesium dissimilar alloys, comprising the following steps:

[0073] Step 1) placing a metal transfer layer between an aluminum alloy plate and a magnesium alloy plate; wherein the aluminum alloy plate and the metal transfer layer form a first area to be welded, and the magnesium alloy plate and the metal transfer layer form a second area to be welded;

[0074] The aluminum alloy plate is a 3 mm thick 6061-T6 aluminum alloy rolled plate, and the magnesium alloy plate is a 3 mm thick ZK60 magnesium alloy rolled plate; a Q235 steel plate is used as a metal transfer layer, and the thickness and width of the metal transfer layer are 3 mm; in addition, before step 1), the surface oxide film on the upper and lower surfaces and the butt joint surface of the aluminum alloy plate, the magnesium alloy plate and the metal transfer layer is mechanically polished, and the oil stains on the contact surface are cleaned with dry cloth dipped in acetone or ethanol; the aluminum alloy plate is butt jointed with the metal transfer layer, and the magnesium alloy plate is butt jointed with the metal transfer layer;

[0075] Step 2) using a stirring head to perform friction stir welding on the first area to be welded, and then using 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 shaft shoulder and a stirring needle. The stirring head is made of H13 steel, the shaft shoulder is a concave shaft shoulder, and the diameter of the concave shaft shoulder is 16mm. The stirring needle is cylindrical, and the surface of the stirring needle has a right-handed thread. The diameter of the stirring needle is 6mm, and the needle length of the stirring needle is 2.8mm. The edge of the stirring needle deviates into the Q235 steel on the forward side of the weld by 0.2mm.

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

[0078] Example 1 utilizes the characteristics of aluminum-steel and magnesium-steel both forming good bonding, transforms the connection between aluminum-magnesium dissimilar alloys into that between aluminum-steel-magnesium alloys, and effectively avoids 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, it can be seen that no welding defects are found in the joints, and the interfaces between the aluminum alloy plate and the metal transfer layer, and between the magnesium alloy plate and the metal transfer layer are well bonded; Figure 3 As shown in (curve 1), the tensile strength of the aluminum-magnesium dissimilar alloy weld joint was measured to be 199 MPa and the elongation was 3.2%.

[0079] Example 2

[0080] See also Figure 1 The present embodiment provides a friction stir welding method for aluminum-magnesium dissimilar alloys, comprising the following steps:

[0081] Step 1) placing a metal transfer layer between an aluminum alloy plate and a magnesium alloy plate; wherein the aluminum alloy plate and the metal transfer layer form a first area to be welded, and the magnesium alloy plate and the metal transfer layer form a second area to be welded;

[0082] The aluminum alloy plate is a 3 mm thick 6061-T6 aluminum alloy rolled plate, and the magnesium alloy plate is a 3 mm thick ZK60 magnesium alloy rolled plate; Q235 steel plate is used as a metal transfer layer, and the thickness of the metal transfer layer is 3 mm and the width is 4 mm; in addition, before step 1), the surface oxide film on the upper and lower surfaces and the butt joint surface of the aluminum alloy plate, the magnesium alloy plate and the metal transfer layer is mechanically polished, and the oil stains on the contact surface are cleaned with dry cloth dipped in acetone or ethanol; the aluminum alloy plate is butt jointed with the metal transfer layer, and the magnesium alloy plate is butt jointed with the metal transfer layer;

[0083] Step 2) firstly stir friction welding is performed on the first area to be welded, and then stir friction 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 shaft shoulder and a stirring needle. The stirring head is made of H13 steel, the shaft shoulder is a concave shaft shoulder, and the diameter of the concave shaft shoulder is 16 mm. The stirring needle is cylindrical, and the surface of the stirring needle has a right-hand thread. The diameter of the stirring needle is 6 mm, and the needle length of the stirring needle is 2.8 mm. The edge of the stirring needle deviates into the Q235 steel on the forward side of the weld by 0.5 mm.

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

[0086] Example 2 utilizes the characteristics of aluminum-steel and magnesium-steel both forming good bonding, transforms the connection between aluminum-magnesium dissimilar alloys into a connection between aluminum-steel-magnesium alloys, and effectively avoids 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, it can be seen that no welding defects are found in the joints, and the interfaces between the aluminum alloy plate and the metal transfer layer, and between the magnesium alloy plate and the metal transfer layer are well bonded; Figure 3 As shown in (curve 2), the tensile strength of the aluminum-magnesium dissimilar alloy weld joint was measured to be 206 MPa and the elongation was 3.7%.

[0087] Comparative Example 1

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

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

[0090] The aluminum alloy plate is a 3 mm thick 6061-T6 aluminum alloy rolled plate, and the magnesium alloy plate is a 3 mm thick ZK60 magnesium alloy rolled plate. In addition, before docking, the surface oxide film of the contact surface of the aluminum alloy plate and the magnesium alloy plate is mechanically polished, and the oil stain on the contact surface is cleaned with dry cloth dipped in acetone or ethanol.

[0091] Step 2) using 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 shaft shoulder and a stirring needle. The stirring head is made of H13 steel, the shaft shoulder is a concave shaft shoulder, and the diameter of the concave shaft shoulder is 16 mm. The stirring needle is cylindrical, and the surface of the stirring needle has a right-handed thread. The diameter of the stirring needle is 6 mm, and the needle length of the stirring needle is 2.8 mm. The aluminum alloy plate is located on the retreat side of the weld. The edge of the stirring needle deviates into the magnesium alloy plate on the forward side of the weld by 0.2 mm.

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

[0094] Compared with the embodiment, the comparative example does not add a metal transition layer between the aluminum-magnesium dissimilar alloy plates, and the microstructure of the obtained welded joint is as follows: Figure 5 As shown, it can be found that there are obvious hole defects in the joint ( Figure 5 a), this is mainly due to the fact that during the welding process, the aluminum and magnesium alloys are mixed together, a eutectic reaction occurs, and a large amount of aluminum-magnesium low-melting-point eutectic compounds are generated at the aluminum-magnesium interface ( Figure 5 b) Its melting point is lower than 450°C, and the center temperature of the weld is as high as 500°C or above. These aluminum-magnesium intermetallic compounds are in liquid state, which makes the welding tool unable to effectively drive the material flow, thus forming a hole defect in the weld; Figure 3 As shown in (curve 3), the tensile strength of the aluminum-magnesium dissimilar alloy weld joint was measured to be 125 MPa and the elongation was 1.2%.

[0095] Comparative Example 2

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

[0097] Step 1) placing a metal interlayer between an aluminum alloy plate and a magnesium alloy plate; wherein the aluminum alloy plate is butted against the metal interlayer, and the magnesium alloy plate is butted against the metal interlayer;

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

[0099] Step 2) using a stirring head to perform single-pass friction stir welding on 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 shaft shoulder and a stirring needle. The stirring head is made of H13 steel, the shaft shoulder is a concave shaft shoulder, and the diameter of the concave shaft shoulder is 16 mm. The stirring needle is cylindrical, and the surface of the stirring needle has a right-handed thread. The diameter of the stirring needle is 6 mm, and the needle length of the stirring needle is 2.8 mm. The edge of the stirring needle deviates into the ZK60 magnesium alloy on the forward side of the weld by 0.5 mm.

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

[0102] Compared with the embodiment, in this comparative example, a metal interlayer (pure iron sheet) is added between the aluminum-magnesium dissimilar alloy plates, and the microstructure of the welded joint obtained by single-pass FSW is as follows: Figure 6 As shown in the figure, it can be found that the metal interlayer in the weld is broken into small fragments, so it does not completely isolate the aluminum-magnesium eutectic reaction. The metal interlayer fragments interfere with the material flow during the stir friction welding process, resulting in welding defects in the weld. Figure 3 As shown in (curve 4), the tensile strength of the aluminum-magnesium dissimilar alloy weld joint was measured to be 150 MPa and the elongation was 1%.

[0103] It is easy for those skilled in the art to understand that, without conflict, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed.

[0104] The above description is only 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 principle of the present invention shall be included in the protection scope of the present invention. The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present invention. These improvements and variations should also be regarded as the protection scope of the present invention.

Claims

1. A friction stir welding method for aluminum-magnesium dissimilar alloys, characterized in that: The following steps are involved: Step 1) placing a metal transfer layer between an aluminum alloy part and a magnesium alloy part; wherein the aluminum alloy part and the metal transfer layer form a first area to be welded, and the magnesium alloy part and the metal transfer layer form a second area to be welded; Step 2) performing friction stir welding on the first area to be welded to metallurgically bond the aluminum alloy part to the metal transfer layer; Stir friction welding is performed on the second area to be welded to metallurgically bond the magnesium alloy part to the metal transfer layer.

2. The friction stir welding method for aluminum-magnesium dissimilar alloys according to claim 1, characterized in that: In the step 1): the metal transfer layer is a metal layer with a thickness of ≥0.5 mm; and / or The metal transfer layer is made of a metal with a melting point higher than 660° C.; preferably, the metal transfer layer is made of one of pure titanium, pure nickel, pure copper, steel, titanium alloy, nickel alloy, and copper alloy; and / or The metal transfer layer is made of a metal that can form an intermetallic compound with an aluminum alloy part or a magnesium alloy part, and the formation temperature of the intermetallic compound is ≥450°C.

3. The friction stir welding method of aluminum-magnesium dissimilar alloys according to claim 1, characterized in that: In the step 1), after the metal transfer layer is placed between the aluminum alloy part and the magnesium alloy part, the connection between the aluminum alloy part and the metal transfer layer, and between the magnesium alloy part and the metal transfer layer are all one of butt joint, butt overlap, and overlap; and / or In the step 2), a stirring head is used to perform friction stir welding; the stirring head comprises a shaft shoulder and a stirring needle.

4. The friction stir welding method for aluminum-magnesium dissimilar alloys according to claim 3, characterized in that: 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; and / or The stirring needle has a cylindrical or conical shape; and / or The end of the stirring needle is flat or spherical; and / or The surface of the stirring needle is smooth, or the surface of the stirring needle has an annular groove or a thread; The length of the stirring needle is 1 to 100 mm; and / or The root diameter of the stirring needle is 3 to 30 mm.

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

6. The friction stir welding method for aluminum-magnesium dissimilar alloys according to claim 4, characterized in that: When the connection method is overlap: The thickness direction of the metal transfer layer is the same as the thickness direction of the aluminum alloy plate; and / or The difference between the needle length of the stirring needle and the thickness of the aluminum alloy plate or the magnesium alloy plate is -0.2 to 0.2 mm; and / or The distance between the end of the stirring needle and the metal transfer layer is ≤0.2 mm or the stirring needle is inserted into the metal transfer layer.

7. The friction stir welding method of aluminum-magnesium dissimilar alloys according to claim 3, characterized in that: 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 to 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 aluminum-magnesium dissimilar alloys according to claim 1, characterized in that: In the step 2): When the first area to be welded is subjected to friction stir welding, the aluminum alloy part is located at the retreat side of the weld; and / or When the second area to be welded is subjected to friction stir welding, the magnesium alloy part is located at the retreat side of the weld.

9. The friction stir welding method of aluminum-magnesium dissimilar alloys according to claim 1, characterized in that: In the step 2): The friction stir welding adopts one of conventional friction stir welding, double-shoulder friction stir welding, differential friction stir welding and static shoulder friction stir welding; Preferably, the welding speed of the friction stir welding is 0.5 to 2000 mm / min.

10. An aluminum-magnesium dissimilar alloy weld joint, characterized in that: The aluminum-magnesium dissimilar alloy welding joint comprises an aluminum alloy part, a magnesium alloy part and a metal transition layer; the aluminum alloy part is metallurgically bonded to the metal transition layer; the magnesium alloy part is metallurgically bonded to the metal transition layer; Preferably, the tensile strength of the aluminum-magnesium dissimilar alloy weld joint is ≥180MPa, and the elongation is ≥2%; Preferably, the aluminum-magnesium dissimilar alloy weld joint is obtained by the stir friction welding method according to any one of claims 1 to 9.

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