Thick plate dissimilar metal friction stir welding method

Abstract

The invention discloses a thick plate dissimilar metal friction stir welding method, which belongs to the technical field of friction stir welding, and comprises the following steps: machining a plurality of U-shaped grooves arranged at intervals in the thickness direction of the to-be-welded surfaces of a low-melting-point to-be-welded workpiece and a high-melting-point to-be-welded workpiece respectively, and arranging the U-shaped grooves in the two to-be-welded workpieces in a staggered manner; after cleaning before welding, the two workpieces to be welded are flush and assembled in a butt joint mode, the U-shaped grooves of the two workpieces to be welded are meshed in a staggered mode, and the advancing sides are set to be high-melting-point workpieces to be welded; the central axis of the stirring needle deviates towards the side of the low-melting-point to-be-welded workpiece and completely covers the whole welding seam interface, and the cylindrical outer circle of the stirring needle intrudes into the high-melting-point to-be-welded workpiece by the thickness of 0.5-2 mm; and welding process parameters are set to implement friction stir welding. The U-shaped groove is prefabricated in the plate thickness direction, two materials are staggered and mixed in the thickness direction before welding, the hardness of the materials on the two sides of a stirring needle is the same in the welding process, the welding process is stable, welding forming is excellent, and thick plate dissimilar metal single-face welding and double-face forming are achieved.

Description

Technical Field

[0001] This invention relates to the field of friction stir welding technology, and specifically to a method for friction stir welding of dissimilar metals in thick plates. Background Technology

[0002] With the continuous development and consumption of Earth's natural resources, restrictions are being placed on the use of scarce resources, especially strategic reserves. To reduce their usage, researching and developing alternative materials is imperative. For example, copper is a good conductor of electricity and heat in the power electronics and automation industries, but it is a scarce and valuable resource. Its use should be conserved and limited. Attempts could be made to use aluminum alloys, which have slightly lower electrical and thermal conductivity, to partially replace copper, combining aluminum and copper to form welded structural components. This would not only reduce the weight of the structure and leverage the advantages of each material, but also lower production costs. Combining magnesium alloys (low density, high specific strength) with aluminum alloys (currently the most widely used non-ferrous metal) to form dissimilar metal welded joints has substantial engineering application value for lightweight structures.

[0003] Welding dissimilar materials such as Al-Cu and Al-Mg is impractical due to the significant differences in their physical and chemical properties and the high likelihood of them reacting to form intermetallic compounds. Traditional fusion welding methods are simply not feasible. Friction stir welding, on the other hand, is more feasible for welding dissimilar metals because it involves low welding temperatures and welding the base materials without melting.

[0004] Currently, methods to improve welding processes, such as matching high stirring head rotation speed with low welding speed, stirring head offset, setting a barrier layer, and optimizing the shape and size of the stirring head, have improved the surface formability of the joints. However, the results are generally poor, and the joint formability and mechanical properties fail to meet application requirements. The key to friction stir welding of dissimilar metals lies in efficiently achieving plastic flow and mixing between the two materials in the weld zone. Therefore, the process requires different heat inputs and pre-mixed materials for the two different materials on the advancing and retreating sides and in the thickness direction. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a method for friction stir welding of dissimilar metals in thick plates, such as Al-Cu and Al-Mg, to achieve friction stir welding of medium and thick plates of dissimilar metals.

[0006] The technical solution adopted in this invention is as follows: A method for friction stir welding of dissimilar metals in thick plates, comprising the following steps: S1. Multiple U-shaped grooves are machined in the thickness direction of the welding surface of the low-melting-point workpiece and the high-melting-point workpiece, respectively, and the U-shaped grooves on the two workpieces are staggered. The width of the U-shaped groove is 1 to 2 mm and the depth is 0.2t to 0.25t, where t is the thickness of the workpiece. S2. After cleaning before welding, assemble the two workpieces to be welded by aligning them together, so that the U-shaped groove of the low melting point workpiece to be welded and the U-shaped groove of the high melting point workpiece to be welded are staggered and meshed, and set the forward side as the high melting point workpiece to be welded. S3. Welding is carried out using a cylindrical stirring pin. The central axis of the stirring pin is offset towards the low-melting-point workpiece and completely covers the entire weld interface. The outer circle of the cylindrical stirring pin penetrates the high-melting-point workpiece by 0.5-2mm. S4. Set welding process parameters and implement friction stir welding.

[0007] Furthermore, in step S4, the welding process parameters meet the requirement of high rotation speed matching low welding speed, and the rotation speed / welding speed ≥ 30.

[0008] Furthermore, the plate thickness t of the workpiece to be welded satisfies 4mm≤t≤20mm.

[0009] Furthermore, the stirring needle has a conical structure with a taper of ≤3°, and the outer circle of the cone is provided with threads and three tangents.

[0010] Furthermore, the material combination of the low-melting-point workpiece and the high-melting-point workpiece is an Al-Cu or Al-Mg dissimilar metal.

[0011] The beneficial effects of this invention are as follows: By prefabricating a U-shaped groove in the thickness direction of the plate, the two materials are mixed alternately in the thickness direction before welding, which averages the hardness level of the advancing side and the retreating side. During the welding process, the materials on both sides of the stirring pin have the same hardness, and the welding is similar to welding between the same materials. The process is stable and the welding formation is better, realizing single-sided welding and double-sided forming of dissimilar metals in thick plates. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the welding process.

[0013] Figure 2 This is a schematic diagram of the pre-welding assembly of the workpiece to be welded.

[0014] Figure 3 This is the assembly diagram of the stirring head.

[0015] Figure 4 This is a schematic diagram of the stirring needle morphology.

[0016] Figure 5 This is a picture showing the welding effect. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] The friction stir welding method for thick plates of dissimilar metals provided by this invention is applicable to the welding of two dissimilar metals with different melting points. The base material can be Al-Cu or Al-Mg, and the plate thickness t of the workpieces to be welded satisfies 4mm ≤ t ≤ 20mm. In this embodiment, the workpieces to be welded are a pure aluminum plate with a length of 300mm and a plate thickness t = 6mm, and a pure copper plate. The operation steps are as follows: S1. Three U-shaped grooves are machined alternately along the thickness direction of the surfaces to be welded on the two workpieces. The width of the U-shaped grooves is 1mm and the depth is 1.5mm (see [reference]). Figure 1 , Figure 2 ); S2. After pre-welding cleaning, assemble the two workpieces to be welded flush, so that the U-shaped groove of the pure aluminum plate and the U-shaped groove of the pure copper plate interlock and mesh, with the forward side set as the pure copper plate workpiece (see...). Figure 1 , Figure 2 ); S3. Welding is performed using a cylindrical stirring pin. The central axis of the stirring pin is offset 1mm towards the pure aluminum plate workpiece and completely covers the entire weld interface. The outer circumference of the cylindrical stirring pin penetrates 0.5mm into the high-melting-point workpiece to be welded (see...). Figure 1 ); S4. Set welding process parameters to implement friction stir welding. The welding process parameters meet the requirement of high rotation speed matching low welding speed, and the rotation speed / welding speed ratio is ≥30. Specifically, in this embodiment, the stirring head rotation speed is set to 900 rpm, and the welding speed is set to 25 mm / min. See the welding effect below. Figure 5 .

[0019] See Figure 3 , Figure 4 In this embodiment, the stirring needle has a conical structure with a taper of ≤3°, and the outer circle of the cone is provided with threads and three tangents.

[0020] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for friction stir welding of dissimilar metals in thick plates, characterized in that, Includes the following steps: S1. Multiple U-shaped grooves are machined in the thickness direction of the welding surface of the low-melting-point workpiece and the high-melting-point workpiece, respectively, and the U-shaped grooves on the two workpieces are staggered. The width of the U-shaped groove is 1 to 2 mm and the depth is 0.2t to 0.25t, where t is the thickness of the workpiece. S2. After cleaning before welding, assemble the two workpieces to be welded by aligning them together, so that the U-shaped groove of the low melting point workpiece to be welded and the U-shaped groove of the high melting point workpiece to be welded are staggered and meshed, and set the forward side as the high melting point workpiece to be welded. S3. Welding is carried out using a cylindrical stirring pin. The central axis of the stirring pin is offset towards the low-melting-point workpiece and completely covers the entire weld interface. The outer circle of the cylindrical stirring pin penetrates the high-melting-point workpiece by 0.5-2mm. S4. Set welding process parameters and implement friction stir welding.

2. The method for friction stir welding of dissimilar metals in thick plates as described in claim 1, characterized in that, In step S4, the welding process parameters meet the requirement of high rotation speed matching low welding speed, and the rotation speed / welding speed ≥ 30.

3. The method for friction stir welding of dissimilar metals in thick plates as described in claim 1, characterized in that, The thickness t of the workpiece to be welded satisfies 4mm≤t≤20mm.

4. The method for friction stir welding of dissimilar metals in thick plates as described in claim 1, characterized in that, The stirring needle has a conical structure with a taper of ≤3°, and the outer circle of the cone is provided with threads and three tangents.

5. The method for friction stir welding of dissimilar metals in thick plates as described in claim 1, characterized in that, The material combination of the low-melting-point workpiece and the high-melting-point workpiece is Al-Cu or Al-Mg dissimilar metal.

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