Method for friction stir welding of magnesium alloy thin-wall shell component

Abstract

The invention discloses a method for friction stir welding of a magnesium alloy thin-wall shell component, which specifically comprises the following steps: step 1, drilling holes are formed in a red copper base plate, every two drilling holes are connected through a hose, and cooling liquid is introduced into the hose; secondly, the shapes of the root and the end of a stirring needle are designed according to the structure of the magnesium alloy thin-wall shell; thirdly, the magnesium alloy thin-wall shell and the magnesium alloy external supporting block are fixed to the red copper base plate; fourthly, a magnesium alloy box cover is placed on the L-shaped connector of the magnesium alloy thin-wall shell in a matched mode; fifthly, the magnesium alloy box cover and the magnesium alloy thin-wall shell are welded together in a micro friction stir welding alternate sectional mode, and a magnesium alloy thin-wall shell component is obtained; and sixthly, the magnesium alloy external supporting block is cut off, welding flashes are removed, and the welding face is polished to be flat. The micro friction stir welding technology is adopted, laser-assisted positioning is combined, the welding path is accurately controlled, more stable plastic metal flow is obtained in the welding process, and high-quality welding of the magnesium alloy thin-wall shell component is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, relates to a magnesium alloy thin-walled shell component, and specifically relates to a method for friction stir welding a magnesium alloy thin-walled shell component. Background Art

[0002] Due to its low density, high specific strength, and excellent electrical conductivity, magnesium alloys have been widely used in fields such as aerospace and automotive manufacturing. With the increasing demand for magnesium alloy thin-walled shell components, their welding technology has gradually become the focus of research. However, the application of magnesium alloy thin-walled shell components in the field of electronic devices faces three welding technology bottlenecks:

[0003] First, the ultra-thin wall thickness characteristic makes it extremely easy for traditional fusion welding to cause burn-through defects due to out-of-control heat input, while conventional friction stir welding is prone to cause base metal collapse due to axial pressure sensitivity. Second, the inherent keyhole in friction stir welding will form a material missing area at the weld termination end, becoming the preferred initiation position for joint fatigue fracture. Third, the semi-closed structure of the L-shaped joint causes the plastic flow metal to easily overflow into the cavity, reducing the functional integrity of the internal precision electronic components. In addition, the asymmetric thermal deformation caused by the welding thermal cycle will reduce the overall dimensional stability of the component, making it difficult to meet the assembly accuracy requirements of electronic devices. These problems jointly restrict the high-reliability welding manufacturing of magnesium alloy thin-walled components.

[0004] To solve the above problems, reasonably distributing heat input to reduce thermal deformation, studying high-precision welding paths, and optimizing the control method of keyholes have become the key directions for the development of the welding technology of magnesium alloy thin-walled shell components with L-shaped joints. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for friction stir welding a magnesium alloy thin-walled shell component to solve the technical problems of welding path deviation, thermal deformation, and material loss in the existing technology.

[0006] To solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0007] A method for friction stir welding a magnesium alloy thin-walled shell component, the method specifically includes the following steps:

[0008] Step 1, drill a number of through holes up and down on a copper backing plate, connect each two drill holes with a hose open at both ends, and make the middle of the hose contact the lower surface of the copper backing plate so that both ends of the hose are located in two drill holes respectively, and coolants are introduced into the hose;

[0009] Step 2, design the shapes of the root and end of the stirring pin according to the structure of the L-shaped joint of the magnesium alloy thin-walled shell;

[0010] Step 3: Fix the magnesium alloy thin-walled shell in Step 2 on the copper backing plate in Step 1, and place magnesium alloy external support blocks around the magnesium alloy thin-walled shell. The magnesium alloy external support blocks are also fixed on the copper backing plate.

[0011] Step 4: Fit and place a magnesium alloy lid on the L-shaped joint of the magnesium alloy thin-walled shell in Step 3. The outer diameter of the magnesium alloy lid is equal to the inner diameter of the magnesium alloy thin-walled shell.

[0012] Step 5: Place the stirring pin in Step 2 into the welding equipment. Combining with the laser-assisted positioning of the welding equipment, use micro friction stir welding to weld the magnesium alloy lid and the magnesium alloy thin-walled shell together in an alternating segmented manner to obtain a magnesium alloy thin-walled shell component, ensuring that the outer side wall of the magnesium alloy thin-walled shell is located on the retreat side of the welding.

[0013] Step 6: Cut off the magnesium alloy external support blocks from the magnesium alloy thin-walled shell component in Step 5, remove the welding flash, and polish the welding surface flat.

[0014] The present invention also has the following technical features:

[0015] In Step 1, the distance between every two drill holes is 10 mm, and the two ends of the hose are respectively located at half of the height in the two drill holes.

[0016] In Step 1, the coolant is a 3:1 mixture of water and paraffin oil, and the coolant flow rate is 5000 mm 3 / s.

[0017] In Step 2, the root of the stirring pin is a cylinder with a diameter of 2.00 - 2.20 mm and a height of 1.60 - 1.80 mm, and the end of the stirring pin is a cone with a diameter of 1.50 - 1.80 mm and a height of 1.20 - 1.40 mm.

[0018] In Step 2, the shoulder type of the stirring pin is concave, and the shoulder diameter of the stirring pin is 10 mm.

[0019] In Step 3, the magnesium alloy external support blocks are of the same height as the magnesium alloy thin-walled shell and can be processed simultaneously.

[0020] In Step 4, the upper surfaces of the magnesium alloy lid, the magnesium alloy external support blocks, and the magnesium alloy thin-walled shell are flush.

[0021] In Step 5, the rotation direction of the stirring pin is counterclockwise.

[0022] The described magnesium alloy thin-walled shell is a hollow cuboid. First, micro friction stir welding is performed on one long side of the magnesium alloy thin-walled shell and the magnesium alloy lid to form a weld seam. Then, micro friction stir welding is successively performed on the other long side and both short sides of the magnesium alloy thin-walled shell and the magnesium alloy lid to form weld seams, achieving segmented welding in an alternating welding sequence.

[0023] The welding rotation speed of the weld seams on both long sides is 1300 - 1600 r / min, and the welding speed of the weld seams on both long sides is 20 - 40 mm / min.

[0024] The welding rotation speed of the weld seams on both short sides is 1400 - 1700 r / min, and the welding speed of the weld seams on both short sides is 20 - 40 mm / min.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] (Ⅰ) The method for friction stir welding of magnesium alloy thin-walled shell components proposed by the present invention, by adopting micro friction stir welding technology and combining laser-assisted positioning, precisely controls the welding path, obtains a more stable plastic metal flow during the welding process, and realizes high-quality welding of magnesium alloy thin-walled shell components.

[0027] (Ⅱ) The method for friction stir welding of magnesium alloy thin-walled shell components proposed by the present invention, compared with the existing welding methods for magnesium alloy thin-walled shell components, extends the welding path in the method provided by the present invention, places the keyhole on the external support block of the magnesium alloy, and avoids the problem of damage to electronic components caused by the existence of the keyhole.

[0028] (Ⅲ) The method for friction stir welding of magnesium alloy thin-walled shell components proposed by the present invention uses stirring pins with different geometric shapes at the root and end, combined with the welding method with the external position on the retreat side, to guide the flow behavior of plastic metal at the L-shaped joint and avoid the plastic metal from flowing into the interior of the magnesium alloy thin-walled shell component.

[0029] (Ⅳ) The method for friction stir welding of magnesium alloy thin-walled shell components proposed by the present invention performs segmented welding in an alternating welding sequence, drills holes in the copper pad with excellent thermal conductivity, and passes in a coolant to accelerate heat dissipation, reducing the problem of large deformation of the magnesium alloy thin-walled shell component caused by the accumulation of heat input during the welding process. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the process of the method for friction stir welding of magnesium alloy thin-walled shell components.

[0031] Figure 2 It is a physical diagram of the stirring pin.

[0032] Figure 3Schematic diagram of the welded finished product of Example 1.

[0033] Figure 4 Schematic diagram of the welded finished product of Example 2.

[0034] Figure 5 Schematic diagram of the welded finished product of Example 3.

[0035] Figure 6 Schematic diagram of the welded finished product of Comparative Example 1.

[0036] Figure 7 Schematic diagram of the post-weld seam of Comparative Example 2.

[0037] Figure 8 Schematic diagram of the cross-section after welding of Comparative Example 3.

[0038] The meanings of each label in the figure are as follows: 1 - copper backing plate, 2 - thin-walled magnesium alloy shell, 3 - stirring pin, 4 - external magnesium alloy support block, 5 - magnesium alloy lid, 6 - weld seam.

[0039] The following further elaborates on the specific content of the present invention in conjunction with examples. Specific Embodiments

[0040] It should be noted that the equipment and materials used in the present invention, unless otherwise specified, are all the equipment and materials known in the prior art.

[0041] The technical concept of the present invention is: to provide a method for friction stir welding of thin-walled magnesium alloy shell components, including using copper with coolant as the backing plate, combining laser-assisted positioning, using stirring pins with different geometric shapes at the root and end for micro friction stir welding, and placing an external magnesium alloy support block during welding to extend the welding path, determining the position of the keyhole according to the set welding parameters and welding path, and completing the micro friction stir welding of the thin-walled magnesium alloy shell components with the determined welding parameters and welding path.

[0042] Following the above technical solutions, the following specific embodiments of the present invention are given. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of this application fall within the protection scope of the present invention.

[0043] Example 1:

[0044] This example proposes a method for friction stir welding of thin-walled magnesium alloy shell components. As Figure 1 shown, the method specifically includes the following steps:

[0045] Step 1: Drill a number of through-holes in the copper backing plate 1. The spacing between every two holes is 10 mm. Connect every two holes with a hose that is open at both ends. The middle part of the hose contacts the lower surface of the copper backing plate 1 so that both ends of the hose are located at half of the height inside two holes respectively. Inject coolant into the hose.

[0046] Preferably in this embodiment, the coolant is a 3:1 mixture of water and paraffin oil, and the flow rate of the coolant is 5000 mm 3 / s.

[0047] Step 2: As Figure 2 shown, design the shapes of the root and the end of the stirring pin 3 according to the structure of the L-shaped joint of the magnesium alloy thin-walled shell 2.

[0048] Preferably in this embodiment, the grade of the magnesium alloy is AZ31.

[0049] Preferably in this embodiment, the thickness of the magnesium alloy thin-walled shell 2 is 2 mm, and the width of the L-shaped joint is 1 mm.

[0050] Preferably in this embodiment, the root of the stirring pin 3 is a cylinder with a diameter of 2.00 mm and a height of 1.60 mm, the end of the stirring pin 3 is a cone with a diameter of 1.50 mm and a height of 1.40 mm, the shoulder type of the stirring pin 3 is concave, and the shoulder diameter of the stirring pin 3 is 10 mm.

[0051] Step 3: Fix the copper backing plate 1 in Step 1 on the workbench, fix the magnesium alloy thin-walled shell 2 in Step 2 on the copper backing plate 1, place magnesium alloy external support blocks 4 around the magnesium alloy thin-walled shell 2. The magnesium alloy external support blocks 4 are of the same height as the magnesium alloy thin-walled shell 2, and the magnesium alloy external support blocks 4 are also fixed on the copper backing plate 1.

[0052] Step 4: Fit and place a magnesium alloy lid 5 on the L-shaped joint of the magnesium alloy thin-walled shell 2 in Step 3. The outer diameter of the magnesium alloy lid 5 is equal to the inner diameter of the magnesium alloy thin-walled shell 2. The upper surfaces of the magnesium alloy lid 5, the magnesium alloy external support blocks 4 and the magnesium alloy thin-walled shell 2 are flush. As Figure 1 shown, first perform micro friction stir welding on the long side of the magnesium alloy thin-walled shell 2 and the magnesium alloy lid 5 to form a weld 6, and then perform micro friction stir welding on the other long side and both short sides of the magnesium alloy thin-walled shell 2 and the magnesium alloy lid 5 in turn to form a weld 6, so as to achieve segmented welding in an alternating welding sequence.

[0053] Preferably, in this embodiment, the welding rotation speed of the welds 6 on both sides of the long side is 1300-1600 r / min, and the welding speed of the welds 6 on both sides of the long side is 20-40 mm / min; the welding rotation speed of the welds 6 on both sides of the short side is 1400-1700 r / min, and the welding speed of the welds 6 on both sides of the short side is 20-40 mm / min.

[0054] Step Five: Place the stirring pin 3 in Step Two into the welding equipment. Combining with the laser-assisted positioning of the welding equipment, use micro friction stir welding to alternately segmentally weld the magnesium alloy lid 5 and the magnesium alloy thin-walled shell 2 together to obtain a magnesium alloy thin-walled shell component, ensuring that the outer wall of the magnesium alloy thin-walled shell 2 is located on the welding retreat side;

[0055] Preferably, in this embodiment, the rotation direction of the stirring pin 3 is counterclockwise rotation.

[0056] Step Six: Cut off the external support block 4 of the magnesium alloy from the magnesium alloy thin-walled shell component in Step Five, remove the welding flash, and polish the welding surface flat.

[0057] After testing, in this embodiment, after micro friction stir welding, the flowing metal during welding did not enter the interior of the magnesium alloy thin-walled component, the surface flatness remained unchanged, and the airtightness after welding was good. As Figure 3 shown, in this embodiment, the high-performance welding of the magnesium alloy thin-walled shell component is completed, the surface flatness of the component before and after welding remains unchanged, and the leakage rate level in the airtightness test reaches the standard of 1×10 -8 Pa / s.

[0058] Example 2:

[0059] The welding method of the magnesium alloy thin-walled shell component proposed in this embodiment is basically the same as that in Example 1, except that: the grade of the magnesium alloy used is ZM51.

[0060] After testing, as Figure 4 shown, in this embodiment, the surface of the magnesium alloy thin-walled shell component after micro friction stir welding is flat and the welding performance is good, the high-quality welding of the magnesium alloy thin-walled shell component is completed, and the leakage rate level in the airtightness test also reaches the standard of 1×10 -8 Pa / s.

[0061] Example 3:

[0062] The welding method of the magnesium alloy thin-walled shell component proposed in this embodiment is basically the same as that in Example 1, except that:

[0063] the thickness of the magnesium alloy thin-walled shell is 3.00 mm, and the width of the L-shaped joint is 1.5 mm.

[0064] The root of the stirring pin 3 is a cylinder with a diameter of 2.20 mm and a height of 1.80 mm, the end of the stirring pin 3 is a cone with a diameter of 1.80 mm and a height of 1.40 mm, the shoulder type of the stirring pin 3 is concave, and the shoulder diameter of the stirring pin 3 is 10 mm.

[0065] The welding rotation speed of the welds 6 on both sides of the long side is 1400 - 1700 r / min, and the welding speed is 20 - 40 mm / min; the welding rotation speed of the welds 6 on both sides of the short side is 1500 - 1800 r / min, and the welding speed is 20 - 40 mm / min.

[0066] After testing, as Figure 5 shown, in this embodiment, the connection performance at the L-shaped joint of the magnesium alloy thin-walled shell component is good, the surface is flat after welding, there is no material loss, and the air leakage rate level reaches the standard of 1×10 -8 Pa / s in the airtightness test.

[0067] Comparative Example 1:

[0068] The welding method of the magnesium alloy thin-walled shell component proposed in this comparative example is basically the same as that in Example 1, the only difference being that the copper backing plate 1 used during welding was not drilled and cooled liquid was not passed through it.

[0069] After experiments, as Figure 6 shown, in this comparative example, during the welding process, the heat dissipation of the magnesium alloy thin-walled shell component was slow, and large thermal deformations occurred. Although excellent welding of the magnesium alloy thin-walled shell component was completed in this comparative example, after welding, the welding surface of the magnesium alloy thin-walled shell component was uneven due to thermal deformation.

[0070] Comparative Example 2:

[0071] The welding method of the magnesium alloy thin-walled shell component proposed in this comparative example is basically the same as that in Example 2, the only difference being that the magnesium alloy thin-walled shell component was not welded in an alternating welding sequence to achieve segmented welding.

[0072] After testing, in this comparative example, as Figure 7 shown, the material loss rate of the magnesium alloy thin-walled shell component during the welding process reached 18 - 25%.

[0073] Comparative Example 3:

[0074] The welding method of the magnesium alloy thin-walled shell component proposed in this comparative example is basically the same as that in Example 3, the only difference being that the magnesium alloy thin-walled shell component used in Example 3 was welded using the micro friction stir welding technology with the retreat side built-in.

[0075] After testing, as Figure 8As shown, in this comparative example, effective connection of the magnesium alloy thin-walled shell component was achieved. However, the connection at the welded joint was not sufficient enough, and collapse and material loss occurred inside the magnesium alloy thin-walled shell component. The integrity of the magnesium alloy thin-walled shell component after welding was lower than that in Example 1.

[0076] It can be seen from Examples 1 to 3 and Comparative Examples 1 to 3 that:

[0077] By using the welding method for the magnesium alloy thin-walled shell component proposed in the present invention, the problem of large deformation of the welded joint of the magnesium alloy thin-walled shell component during the welding process can be effectively avoided. The technical problem of collapse inside the magnesium alloy thin-walled shell component is solved by adopting the alternating segmented welding and the method of placing the retreat side outside. Moreover, the problem of material loss of the component is solved by adopting the method of extending the welding path to place the keyhole on the external support block, realizing high-quality welding of the magnesium alloy thin-walled shell component.

Claims

1. A method for friction stir welding a thin-walled magnesium alloy shell component, characterized in that The method specifically includes the following steps: Step 1: Drill a number of holes that penetrate up and down on the copper backing plate (1). Connect each two holes with a hose that is open at both ends. The middle part of the hose contacts the lower surface of the copper backing plate (1) so that both ends of the hose are located in two holes respectively. Inject coolant into the hose. Step 2: Design the shapes of the root and end of the stirring pin (3) according to the L-shaped joint structure of the magnesium alloy thin-walled shell (2). Step 3: Fix the magnesium alloy thin-walled shell (2) in Step 2 on the copper backing plate (1) in Step 1. Place magnesium alloy external support blocks (4) around the magnesium alloy thin-walled shell (2), and the magnesium alloy external support blocks (4) are also fixed on the copper backing plate (1). Step 4: Fit and place a magnesium alloy lid (5) on the L-shaped joint of the magnesium alloy thin-walled shell (2) in Step 3. The outer diameter of the magnesium alloy lid (5) is equal to the inner diameter of the magnesium alloy thin-walled shell (2). Step 5: Place the stirring pin (3) in Step 2 into the welding equipment. Combining with the laser-assisted positioning of the welding equipment, use micro friction stir welding to weld the magnesium alloy lid (5) and the magnesium alloy thin-walled shell (2) together in an alternating segmented manner to obtain a magnesium alloy thin-walled shell component, ensuring that the outer wall of the magnesium alloy thin-walled shell (2) is located on the welding retreat side. Step 6: Cut off the magnesium alloy external support blocks (4) from the magnesium alloy thin-walled shell component in Step 5, remove the welding flash, and polish the welding surface flat.

2. The method for friction stir welding of a thin-walled magnesium alloy shell component according to claim 1, characterized in that In Step 1, the distance between each two holes is 10 mm, and both ends of the hose are located at half of the height in two holes respectively.

3. The method for friction stir welding a thin-walled magnesium alloy housing component according to claim 1, characterized in that, In Step 1, the coolant is a 3:1 mixture of water and paraffin oil, and the coolant flow rate is 5000mm 3 / s.

4. The method for friction stir welding a thin-walled magnesium alloy housing member according to claim 1, wherein In Step 2, the root of the stirring pin (3) is a cylinder with a diameter of 2.00 - 2.20 mm and a height of 1.60 - 1.80 mm, and the end of the stirring pin (3) is a cone with a diameter of 1.50 - 1.80 mm and a height of 1.20 - 1.40 mm. In Step 2, the shoulder type of the stirring pin (3) is concave, and the shoulder diameter of the stirring pin (3) is 10 mm.

5. The method for friction stir welding a thin-walled magnesium alloy shell component according to claim 1, characterized in that, In Step 3, the magnesium alloy external support blocks (4) are of the same height as the magnesium alloy thin-walled shell (2) and can be processed simultaneously.

6. The method for friction stir welding a thin-walled magnesium alloy housing component according to claim 1, wherein In Step 4, the upper surfaces of the magnesium alloy lid (5), the magnesium alloy external support blocks (4) and the magnesium alloy thin-walled shell (2) are flush.

7. The method for friction stir welding a thin-walled magnesium alloy housing component according to claim 1, characterized in that, In Step 5, the rotation direction of the stirring pin (3) is counterclockwise rotation.

8. The method for friction stir welding a thin-walled magnesium alloy housing component according to claim 1, wherein The magnesium alloy thin-walled shell (2) is a hollow cuboid. First, perform micro friction stir welding on the long side of the magnesium alloy thin-walled shell (2) and the magnesium alloy lid (5) to form a weld seam (6), and then sequentially perform micro friction stir welding on the other long side and the two short sides of the magnesium alloy thin-walled shell (2) and the magnesium alloy lid (5) to form weld seams (6) to achieve segmented welding in an alternating welding sequence.

9. The method for friction stir welding a thin-walled magnesium alloy housing component as claimed in claim 1, wherein, The welding rotation speed of the weld seams (6) on both sides of the long side is 1300 - 1600 r / min, and the welding speed of the weld seams (6) on both sides of the long side is 20 - 40 mm / min. The welding rotation speed of the weld seams (6) on both sides of the short side is 1400 - 1700 r / min, and the welding speed of the weld seams (6) on both sides of the short side is 20 - 40 mm / min.

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