Friction stir welding method for aluminum-magnesium dissimilar alloy of medium plate

Abstract

The invention discloses a friction stir welding method for aluminum-magnesium dissimilar alloy of a medium plate. Firstly, an aluminum alloy plate and a magnesium alloy plate which are equal in thickness (h) are selected, a protruding part is machined in the middle of a to-be-welded interface of the magnesium alloy plate, and meanwhile a concave part matched with the protruding part is prepared in the corresponding position of the aluminum alloy plate; then, the convex part of the magnesium alloy plate is accurately embedded into the concave part of the aluminum alloy plate to form a mechanical embedding structure; and finally, a stirring head is adopted for conducting friction stir welding along the path that the center line of the protruding part deviates towards the aluminum alloy plate side. According to the method, a material flowing track is forcibly regulated and controlled through geometric interlocking design, generation of brittle intermetallic compounds (IMC) is effectively inhibited in combination with an offset welding strategy, and the structural integrity and the mechanical property uniformity of the joint in the thickness direction are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of friction stir welding, and more specifically, to a friction stir welding method for dissimilar aluminum-magnesium alloys of medium-thick plates. Background Art

[0002] In the friction stir welding (FSW) of dissimilar magnesium / aluminum (Mg / Al) metals for medium-thick plates (plate thickness of 6 - 30 mm), brittle Mg-Al intermetallic compounds (IMCs) are extremely likely to form at the interface, seriously deteriorating the joint performance. Summary of the Invention

[0003] Aiming at the defects existing in the prior art, the purpose of the present invention is to provide a friction stir welding method for dissimilar aluminum-magnesium alloys of medium-thick plates, which can effectively inhibit the formation of IMCs and ensure the structural integrity and mechanical property uniformity of the joint in the thickness direction.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is: a friction stir welding method for dissimilar aluminum-magnesium alloys of medium-thick plates, including the following steps: Step S1. Select an aluminum alloy plate and a magnesium alloy plate, and the thickness of both the aluminum alloy plate and the magnesium alloy plate is h; Step S2. Process a convex portion in the middle of the interface to be welded of the magnesium alloy plate; process a concave portion adapted to the convex portion in the middle of the interface to be welded of the aluminum alloy plate; Step S3. Embed the convex portion of the magnesium alloy plate into the concave portion of the aluminum alloy plate; Step S4. Perform friction stir welding using a stirring head, and the welding path of the stirring head is offset from the midline of the convex portion of the magnesium alloy plate towards the aluminum alloy plate side.

[0005] Based on the above technical solution, in Step S1, the thickness h of the aluminum alloy plate and the magnesium alloy plate is 6 - 30 mm.

[0006] Based on the above technical solution, in Step S2, the thickness of the convex portion is 1 / 3h, and the length is not greater than the diameter d of the stirring head.

[0007] Based on the above technical solution, in Step S2, the width of the concave portion is 1 / 3h, and the depth is not greater than the diameter d of the stirring head.

[0008] Based on the above technical solution, in Step S4, the welding path of the stirring head is offset 0.5 - 1 mm from the midline of the convex portion of the magnesium alloy plate towards the aluminum alloy plate side.

[0009] Based on the above technical solution, in Step S4, when the stirring head performs friction stir welding, it presses downward axially.

[0010] Based on the above technical solution, the downward pressing amount of the stirring head is 0.1 - 0.2 mm.

[0011] Based on the above technical solution, in step S4, the diameter d of the stirring head is 0.5 - 1.2 times the plate thickness.

[0012] Based on the above technical solution, in step S4, the rotation speed of the stirring head is 800 - 1100 r / min.

[0013] Based on the above technical solution, in step S4, the welding speed of the friction stir welding is 20 - 40 mm / min.

[0014] The beneficial effects of the present invention are as follows: In the present invention, the offset strategy precisely controls the action areas of the stirring pin and the shoulder, enabling them to simultaneously cover the Mg raised part and the side walls and bottom of the Al concave area. This ensures that sufficient plastic metal flow is generated at the interface and achieves full mechanical interlocking and metallurgical bonding, thereby reliably realizing the connection of dissimilar Al / Mg metals.

[0015] In the present invention, the offset towards the Al side causes the main heat and force action centers of the stirring head to deviate towards the aluminum plate. This significantly reduces the proportion of Mg in the plastic flow zone and decreases the supply of Mg atoms participating in the formation of Mg - Al intermetallic compounds (Mg 17 Al 12 and Mg2Al3).

[0016] In the present invention, the offset towards the Al side combined with the Mg raised / Al concave structure forces the stirring pin to penetrate through thicker Al material (the bottom area of the concave), which prompts the stirring pin to generate stronger downward plastic flow, effectively overcoming the problem of incomplete penetration or weak connection (delamination) between layers caused by insufficient plastic flow during the welding of thick plates in traditional butt welding, ensuring the structural integrity and mechanical property uniformity of the joint in the thickness direction. Description of the Drawings

[0017] Figure 1 is a schematic structural diagram of the stirring head in the present invention; Figure 2 is a schematic structural diagram of the magnesium alloy plate in the present invention; Figure 3 is a schematic structural diagram of the aluminum alloy plate in the present invention; Figure 4 is a schematic diagram of the welding path of the stirring head in the present invention; Figure 5 is a schematic working diagram of the stirring head in the present invention; Figure 6 is a schematic working diagram of the friction stir welding in the present invention; Figure 7 is Figure 6 a cross-sectional view taken along the A - A direction in Figure 8 This is the morphology diagram of the welded joint of aluminum-magnesium dissimilar alloys in Embodiment 1 of the present invention; Figure 9 This is the morphology diagram of the welded joint of aluminum-magnesium dissimilar alloys in Comparative Example 1 of the present invention.

[0018] Reference numerals: 1 - Stirring head; 2 - Magnesium alloy plate; 21 - Protrusion; 3 - Aluminum alloy plate; 31 - Depression. Detailed implementation manners

[0019] The embodiments of the present invention will be described in detail below. The described embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout.

[0020] With reference to the accompanying drawings of the specification, by further describing the specific implementation manners of the present invention, the technical solutions and their beneficial effects of the present invention will be made clearer and more definite. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] See Figure 1 As shown, the present invention provides a friction stir welding method for medium-thick aluminum-magnesium dissimilar alloys, including the following steps: Step S1. See Figures 2 to 3 As shown, an aluminum alloy plate 3 and a magnesium alloy plate 2 are selected, and the thicknesses of both the aluminum alloy plate 3 and the magnesium alloy plate 2 are h; specifically, the thickness h of the aluminum alloy plate 3 and the magnesium alloy plate 2 is 6 - 30 mm.

[0022] Step S2. A protrusion 21 is machined in the middle of the welding interface of the magnesium alloy plate 2; a depression 31 adapted to the protrusion 21 is machined in the middle of the welding interface of the aluminum alloy plate 3; specifically, the thickness of the protrusion 21 is 1 / 3h, and the length is not greater than the diameter d of the stirring head 1. The width of the depression 31 is 1 / 3h, and the depth is not greater than the diameter d of the stirring head 1. See Figure 1 As shown, the diameter d of the stirring head 1 is 0.5 - 1.2 times the plate thickness.

[0023] Step S3. The protrusion 21 of the magnesium alloy plate 2 is inserted into the depression 31 of the aluminum alloy plate 3; Step S4. See Figures 4 to 7 As shown, friction stir welding is performed using the stirring head 1, and the welding path of the stirring head 1 is offset from the midline of the protrusion 21 of the magnesium alloy plate ² towards the aluminum alloy plate 3 side. Specifically, the welding path of the stirring head 1 is offset from the midline of the protrusion 21 of the magnesium alloy plate 2 towards the aluminum alloy plate 3 side by 0.5 - 1 mm. The rotational speed of the stirring head 1 is 800 - 1100 r / min. In Step S4, the welding speed of the friction stir welding is 20 - 40 mm / min. SeeFigure 5 As shown in Figure 5 , when the stirring head 1 performs friction stir welding, it presses downward along the axis. Specifically, the downward pressing amount of the stirring head 1 is 0.1 - 0.2 mm. Example

[0024] Select the aluminum alloy plate as 6061 - T6 aluminum alloy and the magnesium alloy plate as AZ31B - H24 magnesium alloy, with a plate thickness of 6 mm for both. Process a convex part 21 in the middle of the welding surface of the magnesium alloy plate, with a thickness of 2 mm and a length of 3 mm; process a concave part 31 in the corresponding position on the aluminum alloy plate, with a width of 2 mm and a depth of 3 mm. Clean and wipe the interface with alcohol, and butt - joint to form the area to be welded. The material of the stirring head is H13 steel, and the width of the stirring head is 3 mm. The welding path of the stirring head is offset 0.5 mm towards the aluminum alloy plate side. The process parameters of friction stir welding are: rotational speed is 1000 rpm, welding speed is 30 mm / min, and the downward pressing amount of the shoulder is 0.15 mm.

[0025] Example 1 reduces the supply of intermetallic compound Mg by using the concave - convex structure. Figure 8 For the micro - structure morphology of the joint cross - section, it is found that the aluminum alloy and the magnesium alloy are interlaced to form an obvious eddy - like structure. Through EDS and XRD analysis, the intermetallic compound phases in the welded joint area are Mg2Al3 and Mg 17 Al 12 , and a dense and defect - free weld seam is formed. The magnesium alloy and the aluminum alloy are evenly mixed in the weld nugget area, promoting the metallurgical bonding between the two, increasing the joint strength. Its tensile strength reaches a maximum of 168 MPa, which is 61% of the strength of the AZ31B base material. The experimental results at different rotational speeds are shown in Table 1.

[0026]

[0027] Comparative Example 1 Place the metal transition layer between the aluminum alloy plate and the magnesium alloy plate; among them, 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. Among them, the aluminum alloy plate is a 3 - mm - thick 6061 - T6 aluminum alloy rolled plate, the magnesium alloy plate is a 3 - mm - thick ZK60 magnesium alloy rolled plate; use a Q235 steel plate as the metal transition layer, with a thickness of 3 mm and a width of 3 mm; in addition, before step 1), mechanically grind the surface oxide films on the upper, lower surfaces and the butt - joint surfaces of the aluminum alloy plate, the magnesium alloy plate and the metal transition layer, and use dry cloth to dip acetone or ethanol to clean the oil stains on the contact surfaces to be joined; among them, the aluminum alloy plate is butt - jointed with the metal transition layer, and the magnesium alloy plate is butt - jointed with the metal transition layer. Friction stir welding is carried out on the first area to be welded using a stirring head, and then friction stir welding is carried out on the second area to be welded using the stirring head to obtain an aluminum-magnesium dissimilar alloy welded joint; During the friction stir welding process, both the aluminum alloy plate and the magnesium alloy plate are located on the retreat side of the weld seam. The welding process parameters are: the rotational speed is 800 rpm, and the welding speed is 50 mm / min.

[0028] Compared with the embodiment, in the comparative example, a metal transition layer is added to connect the aluminum-magnesium dissimilar alloy by double-pass welding. The method is to avoid mixing between aluminum and magnesium. The microstructure of the obtained joint is as Figure 9 shown, and it can be found that Figure 9 (c)obviously pores are found, mainly because in the welding process, double-pass welding makes the aluminum and magnesium sides mix together, and a low-melting eutectic compound is generated at the interface, thus forming pores in the weld seam. The process of this comparative example is more complex than that of the embodiment. A metal transition layer needs to be added, and there are requirements for the positioning device; double-pass welding needs to be carried out, increasing the time cost.

[0029] The present invention effectively suppresses the generation of brittle intermetallic compounds (IMCs) by geometric interlocking design to forcibly regulate the material flow trajectory and combining an offset welding strategy, ensuring the structural integrity and mechanical property uniformity of the joint in the thickness direction.

[0030] In the description of the specification, the description with reference to terms such as "an embodiment", "preferably", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. The schematic description of the above terms in this specification does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.

[0031] The present invention is not limited to the above embodiments. For those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and retouches can be made, and these improvements and retouches are also regarded as within the protection scope of the present invention. The content not described in detail in this specification belongs to the prior art well known to those of ordinary skill in the art.

Claims

1. A friction stir welding method for medium-thick aluminum-magnesium dissimilar alloys, characterized in that It includes the following steps: Step S1. Select an aluminum alloy plate (3) and a magnesium alloy plate (2), and the thicknesses of both the aluminum alloy plate (3) and the magnesium alloy plate (2) are h; Step S2. Process a convex portion (21) in the middle of the welding interface of the magnesium alloy plate (2); process a concave portion (31) adapted to the convex portion (21) in the middle of the welding interface of the aluminum alloy plate (3); Step S3. Insert the convex portion (21) of the magnesium alloy plate (2) into the concave portion (31) of the aluminum alloy plate (3); Step S4. Perform friction stir welding using a stirring head (1), and the welding path of the stirring head (1) is offset from the center line of the convex portion (21) of the magnesium alloy plate (2) towards the aluminum alloy plate (3) side.

2. The friction stir welding method for medium-thick aluminum-magnesium dissimilar alloys as described in claim 1, characterized in that: In step S1, the thickness h of the aluminum alloy plate (3) and the magnesium alloy plate (2) is 6 - 30 mm.

3. The friction stir welding method for medium-thick aluminum-magnesium dissimilar alloys according to claim 1, characterized in that: In step S2, the thickness of the convex portion (21) is 1 / 3h, and the length is not greater than the diameter d of the stirring head (1).

4. The friction stir welding method for medium-thick aluminum-magnesium dissimilar alloys according to claim 1, characterized in that: In step S2, the width of the concave portion (31) is 1 / 3h, and the depth is not greater than the diameter d of the stirring head (1).

5. The friction stir welding method for medium-thick aluminum-magnesium dissimilar alloys as described in claim 1, characterized in that: In step S4, the welding path of the stirring head (1) is offset 0.5 - 1 mm from the center line of the convex portion (21) of the magnesium alloy plate (2) towards the aluminum alloy plate (3) side.

6. The friction stir welding method for medium-thick aluminum-magnesium dissimilar alloys as described in claim 1, characterized in that: In step S4, when the stirring head (1) performs friction stir welding, it is axially pressed down by 0.1 - 0.2 mm, the diameter d of the stirring head (1) is 0.5 - 1.2 times the plate thickness, the rotation speed is 800 - 1100 r / min, and the welding speed is 20 - 40 mm / min.

Images