Continuous local heat treatment strengthening device and method for aluminum alloy friction stir welding seam

Abstract

The invention discloses a friction stir welding seam local heat treatment strengthening device and method, and belongs to the technical field of heat treatment. The device is mainly composed of a large-current pulse power supply, a conductive wheel, a conductive wheel pressing mechanism, a thermal imager, a rapid cooling system and a C-shaped jaw; the large-current pulse power supply can generate pulse current with adjustable frequency and current, the pulse current is introduced into the friction stir welding seam through the pair of conductive wheels to conduct self-resistance heating on the welding seam, the conductive wheel pressing mechanism tightly presses the conductive wheels on the surface of the welding seam, and the thermal imager checks the temperature of electrified self-resistance heating. And the rapid cooling system is used for rapidly cooling the heated part. By applying the device, local heat treatment can be performed on the stirring friction long welding seam, the welding seam structure is improved, the mechanical property of the welding seam is improved, and internal stress and welding deformation around the welding seam are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment, and in particular relates to a device and method for continuous local heat treatment strengthening of aluminum alloy friction stir welds. Background Art

[0002] Friction stir welding is a joining method invented and patented by the British Welding Institute in 1991. It has the advantages of short processing time, low consumables cost, low peak temperature and high joint quality. Friction stir welding can join metals in a hot solid state without welding defects such as cast structure, element loss and pores. Therefore, it is more attractive for welding light alloys such as Mg and Al that are difficult to weld with traditional fusion welding. In the more than 20 years since the advent of FSW technology, it has developed into a mature joining method, showing high strength and efficiency in the joining of other dissimilar materials such as aluminum alloys, magnesium alloys, titanium alloys, polymers, etc. Due to the excellent performance of FSW joints, it is widely used in aerospace, defense, railways, renewable energy, rail vehicles, automobiles and other fields, and is known as the "second revolution in welding history" after laser welding.

[0003] Aluminum and aluminum alloys are considered to be the most promising structural materials in the future aerospace, automotive and other fields due to their good castability, recyclability, low density and high specific strength. Stir friction welding is particularly widely used in aluminum alloy connections. However, since stir friction is essentially a process in which the friction between the rotating tool and the workpiece generates heat to connect the workpieces to be welded, the welding heat input has a significant effect on the microstructure and mechanical properties of the joint. For aluminum alloy stir friction welding, the mechanical properties of the weld and heat-affected zone are significantly lower than those of the parent material. In addition, the outstanding features of FSW are obvious strain gradients, strain rate gradients, temperature gradients and special material flow. This leads to a large grain size gradient in the FSW joint, uneven texture distribution and internal stress. The inhomogeneity of the microstructure and internal stress in the FSW joint will have a great influence on the mechanical properties and fracture behavior of the joint. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a continuous local heat treatment strengthening device and method for aluminum alloy stir friction welds, which realizes basic heat treatment of the stir friction welds by rapid heating and cooling of the stir friction welds, improves grain size and reduces internal stress, thereby improving the mechanical properties of the stir friction welded joints.

[0005] The technical solution adopted by the present invention is specifically as follows:

[0006] A continuous local heat treatment strengthening device for a friction stir weld, the device mainly comprises a continuous local rapid heating system for a friction stir weld, a thermal imager, a continuous local rapid cooling system and a compressed air source;

[0007] The continuous local rapid heating system implements self-resistance heating on the local weld, and the system is composed of a large current pulse power supply 18 and a conductive wheel and a conductive wheel clamping mechanism; the conductive wheel and the conductive wheel clamping mechanism are composed of a C-shaped jaw 1, a pressure reducing valve 2, a pressure gauge 3, a clamping cylinder 4, an upper insulating pad 5, an upper conductive wheel mounting seat 6, an upper conductive wheel shaft 7, an upper conductive wheel 8, a lower conductive wheel 10, a lower conductive wheel shaft 11, a lower conductive wheel mounting seat 12 and a lower insulating pad 13;

[0008] Among them, the upper conductive wheel 8 and the lower conductive wheel 10 are respectively mounted on the upper conductive wheel mounting seat 6 and the lower conductive wheel mounting seat 12 through the upper conductive wheel shaft 7 and the lower conductive wheel shaft 11; the upper conductive wheel mounting seat 6 is isolated and mounted on the plunger of the clamping cylinder 4 through the upper insulating pad 5, and the clamping cylinder 4 is mounted on the upper anvil of the C-shaped jaw 1; the lower conductive wheel mounting seat 12 is isolated and mounted on the lower anvil of the C-shaped jaw 1 through the lower insulating pad 13; the compressed air output by the compressed air source is passed into the clamping cylinder 4 through the pressure reducing valve 2 and the pressure gauge 3, driving the upper conductive wheel 8 and the lower conductive wheel 10 to contact and clamp the upper and lower surfaces of the workpiece;

[0009] The current and frequency output by the high-current pulse power supply 18 are both adjustable; the two poles of the output of the high-current pulse power supply 18 are respectively connected to the upper conductive wheel 8 and the lower conductive wheel 10 through cables, and the current output by the high-current pulse power supply 18 is passed through the upper conductive wheel 8 and the lower conductive wheel 10 into the contact part of the workpiece to achieve rapid self-resistance heating of the contact part of the workpiece, and the continuous movement of the workpiece will achieve continuous local rapid heating of the entire weld.

[0010] The thermal imager 22 is mounted on the C-shaped jaw 1 and is aimed at the contact portion between the workpiece and the upper conductive wheel 8 and the lower conductive wheel 10 (ie, the self-resistance heating portion) to detect the heating temperature of the portion.

[0011] The compressed air source is mainly composed of a screw air compressor 19, an air storage tank 20 and a refrigerated dryer 21. The compressed air generated by the screw air compressor 19 is output after being stabilized by the air storage tank 20 and cooled and dried by the refrigerated dryer 21.

[0012] The rapid cooling system is mainly composed of an upper vortex tube 17, an upper vortex tube outlet hose nozzle 16, a lower vortex tube 14 and a lower vortex tube outlet hose nozzle 15. The upper vortex tube 17 and the lower vortex tube 14 are respectively installed on the upper insulating pad 5 and the lower insulating pad 13. The compressed air output by the compressed air source is passed into the upper vortex tube 17 and the lower vortex tube 14; the compressed air flowing through the upper vortex tube 17 and the lower vortex tube 14 will be cooled and sprayed from the upper vortex tube outlet hose nozzle 16 and the lower vortex tube outlet hose nozzle 15 behind the current contact area of ​​the workpiece, thereby realizing rapid cooling of the upper and lower surfaces of the processed area.

[0013] The present invention provides a method for continuous local heat treatment strengthening of aluminum alloy friction stir welds, and the specific process is as follows:

[0014] Step 1, setting the parameters of the high current pulse power supply 18: setting the output current and frequency of the high current pulse power supply 18 according to the process parameters;

[0015] Step 2, adjusting the clamping force of the conductive wheel: placing the workpiece to be processed between the upper conductive wheel 8 and the lower conductive wheel 10, and adjusting the output pressure of the pressure reducing valve 2 according to the process parameters to the clamping force value required by the process;

[0016] Step 3, welding seam heating: Turn on the high current pulse power supply 18, the pulse current passes through the upper conductive wheel 8 and the lower conductive wheel 10 to implement self-resistance heating on the contact part of the workpiece, and the thermal imager 22 detects the heating temperature.

[0017] Step 4, welding seam cooling: after the temperature detected by the thermal imager 22 reaches the required value, the workpiece is fed, and the high current pulse power supply 18 continues to supply power to heat the next section of the workpiece. At the same time, compressed air is passed into the upper vortex tube 17 and the lower vortex tube 14, and the cold air flow ejected through the upper vortex tube outlet hose nozzle 16 and the lower vortex tube outlet hose nozzle 15 directly acts on the heated part to quickly cool the welding seam.

[0018] Step 5, continue the process of step 4 until the entire weld is processed.

[0019] Before performing local heat treatment of the friction stir weld, it is necessary to determine the optimal process parameters of the welded material. The process of determining the optimal process parameters of the welded material in the present invention is as follows:

[0020] First, multiple samples are cut from the workpiece; then, after clamping them between the upper conductive wheel 8 and the lower conductive wheel 10, a large current pulse power supply 18 passes a pulse current to locally heat the samples, and a thermal imager detects the temperature of the self-resistance heating part; after heating to a certain temperature, a rapid cooling system rapidly cools the heated part; by performing heat treatment tests with different clamping forces, different currents, different heating frequencies and different heating temperatures on multiple samples, the microstructure and mechanical properties of the above samples are compared and analyzed, and the optimal heat treatment process parameters including clamping force, current, frequency and heating temperature are determined.

[0021] The above-mentioned device and method are suitable for strengthening treatment of various plate stir friction welds, and can also strengthen long welds of plate arc welding, that is, the workpiece is a plate stir friction welding workpiece or a plate arc welding workpiece.

[0022] Beneficial effects of the present invention:

[0023] 1. The device and method are used to achieve continuous local heat treatment by rapidly heating and rapidly cooling the aluminum alloy friction stir weld, which can effectively refine the structure of the weld and the heat-affected zone, reduce or eliminate the stress in the weld area, and improve the mechanical properties of the weld.

[0024] 2. The device and method proposed in the present invention are used to perform heat treatment on the friction stir weld, and rapid heating and rapid cooling are only performed on the basic area of ​​the weld, which effectively prevents the weld from being deformed. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the device of the present invention;

[0026] Figure 2 is a side view of the device of the present invention, illustrating the rotation of the conductive wheel and the feeding of the friction stir welding workpiece;

[0027] Figure 3 The mechanical property curves of aluminum alloy friction stir welds before and after continuous local heat treatment strengthening;

[0028] Figure 4 Photos of tensile specimens of aluminum alloy friction stir welds before and after continuous local heat treatment strengthening;

[0029] In the figure: 1-C-type jaws, 2-pressure reducing valve, 3-pressure gauge, 4-clamping cylinder, 5-upper insulating pad, 6-upper conductive wheel mounting seat, 7-upper conductive wheel shaft, 8-upper conductive wheel, 9-friction stir weldment, 10-lower conductive wheel, 11-lower conductive wheel shaft, 12-lower conductive wheel mounting seat, 13-lower insulating pad, 14-lower vortex tube, 15-lower vortex tube outlet hose nozzle, 16-upper vortex tube outlet hose nozzle, 17-upper vortex tube, 18-high current power supply, 19-screw air compressor, 20-gas storage tank, 21-refrigerated dryer, 22-thermal imager. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further explained and illustrated in the form of specific embodiments below.

[0031] Reference Figure 1 and Figure 2 The present invention provides a continuous local heat treatment strengthening device for a friction stir weld, which mainly comprises a continuous local rapid heating system for a friction stir weld, a thermal imager, a continuous local rapid cooling system and a compressed air source;

[0032] The continuous local rapid heating system implements self-resistance heating on the local weld, and the system is composed of a large current pulse power supply 18 and a conductive wheel and a conductive wheel clamping mechanism; the conductive wheel and the conductive wheel clamping mechanism are composed of a C-shaped jaw 1, a pressure reducing valve 2, a pressure gauge 3, a clamping cylinder 4, an upper insulating pad 5, an upper conductive wheel mounting seat 6, an upper conductive wheel shaft 7, an upper conductive wheel 8, a lower conductive wheel 10, a lower conductive wheel shaft 11, a lower conductive wheel mounting seat 12 and a lower insulating pad 13;

[0033] Among them, the upper conductive wheel 8 and the lower conductive wheel 10 are respectively installed on the upper conductive wheel mounting seat 6 and the lower conductive wheel mounting seat 12 through the upper conductive wheel shaft 7 and the lower conductive wheel shaft 11; the upper conductive wheel mounting seat 6 is isolated and installed on the plunger of the clamping cylinder 4 through the upper insulating pad 5, and the clamping cylinder 4 is installed on the upper anvil of the C-shaped jaw 1; the lower conductive wheel mounting seat 12 is isolated and installed on the lower anvil of the C-shaped jaw 1 through the lower insulating pad 13; the compressed air output by the compressed air source is passed into the clamping cylinder 4 through the pressure reducing valve 2 and the pressure gauge 3, driving the upper conductive wheel 8 and the lower conductive wheel 10 to contact and clamp the upper and lower surfaces of the stir friction welding workpiece 9;

[0034] The current and frequency output by the high-current pulse power supply 18 are both adjustable; the two poles of the output of the high-current pulse power supply 18 are respectively connected to the upper conductive wheel 8 and the lower conductive wheel 10 through cables, and the current output by the high-current pulse power supply 18 is passed through the upper conductive wheel 8 and the lower conductive wheel 10 into the contact part of the stir friction welding workpiece 9, thereby realizing rapid self-resistance heating of the contact part of the stir friction welding workpiece 9, and the continuous movement of the stir friction welding workpiece 9 will realize continuous local rapid heating of the entire weld.

[0035] The thermal imager 22 is mounted on the C-shaped jaw 1 and is aimed at the contact portion between the friction stir welding workpiece 9 and the upper conductive wheel 8 and the lower conductive wheel 10 (ie, the self-resistance heating portion) to detect the heating temperature of the portion.

[0036] The compressed air source is mainly composed of a screw air compressor 19, an air storage tank 20 and a refrigerated dryer 21. The compressed air generated by the screw air compressor 19 is output after being stabilized by the air storage tank 20 and cooled and dried by the refrigerated dryer 21.

[0037] The rapid cooling system is mainly composed of an upper vortex tube 17, an upper vortex tube outlet hose nozzle 16, a lower vortex tube 14 and a lower vortex tube outlet hose nozzle 15. The upper vortex tube 17 and the lower vortex tube 14 are respectively installed on the upper insulating pad 5 and the lower insulating pad 13. The compressed air output by the compressed air source is passed into the upper vortex tube 17 and the lower vortex tube 14; the compressed air flowing through the upper vortex tube 17 and the lower vortex tube 14 will be cooled and sprayed from the upper vortex tube outlet hose nozzle 16 and the lower vortex tube outlet hose nozzle 15 behind the current contact area of ​​the stir friction weldment 9, thereby realizing rapid cooling of the upper and lower surfaces of the processed area.

[0038] Example 1 and Example 2 provide continuous local heat treatment strengthening of 6082 aluminum alloy friction stir weld with different parameters, and compare the mechanical properties after treatment.

[0039] Example 1 (PC-90s)

[0040] Step 1: Set the parameters of the high current pulse power supply 18: voltage is 1.2V, current is 65A / mm 2 , frequency 10KHz;

[0041] Step 2, adjusting the clamping force of the conductive wheel: placing the 6082 aluminum alloy friction stir welding workpiece between the upper conductive wheel 8 and the lower conductive wheel 10, and adjusting the output pressure of the pressure reducing valve 2 to a clamping force of 2KN;

[0042] Step 3, welding seam heating: Turn on the high current pulse power supply 18, the pulse current passes through the upper conductive wheel 8 and the lower conductive wheel 10 to implement self-resistance heating on the contact part of the stir friction welding workpiece 9, and the thermal imager 22 detects the heating temperature to 200°C.

[0043] Step 4, weld cooling: After the temperature detected by the thermal imager 22 reaches 200°C, the stir friction welding workpiece 9 is fed, and the high current pulse power supply 18 continues to supply power to heat the lower section of the stir friction welding workpiece 9. At the same time, compressed air is passed into the upper vortex tube 17 and the lower vortex tube 14, and the cold air flow ejected from the upper vortex tube outlet hose nozzle 16 and the lower vortex tube outlet hose nozzle 15 directly acts on the heated part to quickly cool the weld.

[0044] Step 5, continue the process of step 4 until the entire weld is processed.

[0045] Example 2 (PC-210s)

[0046] Step 1: Set the pulse power supply 1 parameters: voltage is 1.2V, current is 65A / mm 2 , frequency 10KHz;

[0047] Step 2, adjusting the clamping force of the conductive wheel: placing the 6082 aluminum alloy friction stir welding workpiece between the upper and lower conductive wheels 8 and 10, and adjusting the output pressure of the pressure reducing valve 2 to a clamping force of 2KN;

[0048] Step 3, welding seam heating: turn on the pulse power supply 1, the pulse current passes through the upper and lower conductive wheels 8 and 10 to implement self-resistance heating on the contact part of the stir friction welding workpiece 9, and the thermal imager 22 detects the heating temperature to 300°C.

[0049] Step 4, weld cooling: After the temperature detected by the thermal imager 22 reaches 300°C, the stir friction welding workpiece is fed, and the pulse power supply 1 continues to supply power to heat the next section of the stir friction welding workpiece. At the same time, compressed air is introduced into the upper and lower vortex tubes 17 and 14, and the cold air flow ejected from the upper and lower vortex tube outlet hose nozzles 16 and 15 directly acts on the heated part to quickly cool the weld.

[0050] Step 5, continue the process of step 4 until the entire weld is processed.

[0051] The mechanical properties test curves of the above two embodiments and the 6082 aluminum alloy friction stir welding workpiece that has not been subjected to overheat treatment for comparison are as follows: Figure 3 The test results are shown in the photo Figure 4 As shown, it can be seen from the comparison that this embodiment provides a method for a continuous local heat treatment strengthening device for a friction stir weld, which can improve the mechanical properties of the weld of a friction stir welded workpiece by rapidly heating and rapidly cooling the weld.

[0052] In order to determine the optimal process parameters for the material being welded, the following methods can be used:

[0053] First, multiple samples are cut from the stir friction welding workpiece 9; then, after clamping it between the upper conductive wheel 8 and the lower conductive wheel 10, a large current pulse power supply 18 passes a pulse current to locally heat the sample, and a thermal imager detects the temperature of the self-resistance heating part; after heating to a certain temperature, a rapid cooling system quickly cools the heated part; by performing heat treatment tests with different clamping forces, different currents, different heating frequencies and different heating temperatures on multiple samples, the microstructure and mechanical properties of the above samples are compared and analyzed, and the optimal heat treatment process parameters including clamping force, current, frequency and heating temperature are determined.

[0054] In addition, the above content is only an exemplary embodiment of the embodiment of the present invention and cannot be considered to limit the scope of implementation of the embodiment of the present invention. The present invention is not only applicable to the continuous local heat treatment strengthening of aluminum alloy stir friction welds, but also to the continuous local heat treatment strengthening of stir friction welds of other metal materials, and also to the continuous local heat treatment strengthening of long welds such as arc welding.

Claims

1. A continuous local heat treatment strengthening device for friction stir welds, It is characterized in that The device is mainly composed of a continuous local rapid heating system for the friction stir weld, a thermal imager, a continuous local rapid cooling system and a compressed air source; The continuous local rapid heating system is composed of a large current pulse power supply (18) and a conductive wheel and a conductive wheel clamping mechanism; the conductive wheel and the conductive wheel clamping mechanism are composed of a C-shaped jaw (1), a pressure reducing valve (2), a pressure gauge (3), a clamping cylinder (4), an upper insulating pad (5), an upper conductive wheel mounting seat (6), an upper conductive wheel shaft (7), an upper conductive wheel (8), a lower conductive wheel (10), a lower conductive wheel shaft (11), a lower conductive wheel mounting seat (12) and a lower insulating pad (13); The upper conductive wheel (8) and the lower conductive wheel (10) are respectively mounted on the upper conductive wheel mounting seat (6) and the lower conductive wheel mounting seat (12) via the upper conductive wheel shaft (7) and the lower conductive wheel shaft (11); the upper conductive wheel mounting seat (6) is mounted on the plunger of the clamping cylinder (4) in isolation via the upper insulating pad (5), and the clamping cylinder (4) is mounted on the upper anvil of the C-shaped jaw (1); the lower conductive wheel mounting seat (12) is mounted on the lower anvil of the C-shaped jaw (1) in isolation via the lower insulating pad (13); the compressed air output by the compressed air source is passed into the clamping cylinder (4) via the pressure reducing valve (2) and the pressure gauge (3), so as to drive the upper conductive wheel (8) and the lower conductive wheel (10) to contact and clamp the upper and lower surfaces of the workpiece; The current and frequency output by the high-current pulse power supply (18) are both adjustable; the two poles of the high-current pulse power supply (18) are respectively connected to the upper conductive wheel (8) and the lower conductive wheel (10) through cables; the current output by the high-current pulse power supply (18) is passed through the upper conductive wheel (8) and the lower conductive wheel (10) into the contact part of the workpiece to achieve rapid self-resistance heating of the contact part of the workpiece; the continuous movement of the workpiece will achieve continuous local rapid heating of the entire weld; The rapid cooling system mainly comprises an upper vortex tube (17), an upper vortex tube outlet hose nozzle (16), a lower vortex tube (14) and a lower vortex tube outlet hose nozzle (15). The upper vortex tube (17) and the lower vortex tube (14) are respectively mounted on an upper insulating pad (5) and a lower insulating pad (13). Compressed air outputted by a compressed air source is passed into the upper vortex tube (17) and the lower vortex tube (14). The compressed air flowing through the upper vortex tube (17) and the lower vortex tube (14) will be cooled and sprayed from the upper vortex tube outlet hose nozzle (16) and the lower vortex tube outlet hose nozzle (15) to the rear of the current contact area of ​​the workpiece, thereby realizing rapid cooling of the upper and lower surfaces of the processed area. The thermal imager (22) is used to detect the heating temperature of the self-resistance heating part; The compressed air source is used to provide compressed air to the rapid cooling system and the continuous local rapid heating system.

2. The continuous local heat treatment strengthening device for friction stir welds according to claim 1, It is characterized in that The thermal imager (22) is mounted on the C-shaped jaw (1) and is aimed at the contact portion between the workpiece and the upper conductive wheel (8) and the lower conductive wheel (10).

3. The continuous local heat treatment strengthening device for friction stir weld according to claim 1, It is characterized in that The compressed air source is mainly composed of a screw air compressor (19), an air storage tank (20) and a refrigerated dryer (21). The compressed air generated by the screw air compressor (19) is output after being stabilized by the air storage tank (20) and cooled and dried by the refrigerated dryer (21).

4. A method for continuous local heat treatment strengthening of aluminum alloy friction stir welds based on the device as claimed in claim 1, It is characterized in that The specific process of this method is as follows: Step (1), setting parameters of a high current pulse power supply (18): setting the output current and frequency of the high current pulse power supply (18) according to the process parameters; Step (2), adjusting the clamping force of the conductive wheel: placing the workpiece to be processed between the upper conductive wheel (8) and the lower conductive wheel (10), and adjusting the output pressure of the pressure reducing valve (2) according to the process parameters to the clamping force value required by the process; Step (3), welding seam heating: a high current pulse power source (18) is turned on, the pulse current is passed through the upper conductive wheel (8) and the lower conductive wheel (10) to implement self-resistance heating on the contact part of the workpiece, and the thermal imager (22) detects the heating temperature. Step (4), welding seam cooling: after the temperature detected by the thermal imager (22) reaches the required value, the workpiece is fed, and the high current pulse power supply (18) is continuously powered to heat the next section of the workpiece. At the same time, compressed air is passed into the upper vortex tube (17) and the lower vortex tube (14), and the cold air flow ejected through the upper vortex tube outlet hose nozzle (16) and the lower vortex tube outlet hose nozzle (15) directly acts on the heated part to quickly cool the welding seam. Step (5), continue the process of step (4) until the entire weld is processed.

5. The method for strengthening the aluminum alloy friction stir weld by continuous local heat treatment according to claim 4, It is characterized in that Before performing local heat treatment of the friction stir weld, it is necessary to determine the optimal process parameters of the welded material. The process of determining the optimal process parameters of the welded material in the present invention is as follows: First, multiple samples are cut from a workpiece; then, after clamping the workpiece between an upper conductive wheel (8) and a lower conductive wheel (10), a large current pulse power supply (18) passes a pulse current to locally heat the sample, and a thermal imager detects the temperature of the self-resistance heating portion; after heating to a certain temperature, a rapid cooling system rapidly cools the heated portion; and heat treatment tests with different clamping forces, different currents, different heating frequencies, and different heating temperatures are performed on multiple samples, and the microstructures and mechanical properties of the samples are compared and analyzed to determine the optimal heat treatment process parameters including clamping force, current, frequency, and heating temperature.

6. The aluminum alloy friction stir weld continuous local heat treatment strengthening method according to claim 4 or 5, It is characterized in that The workpiece is a plate friction stir welding workpiece or a plate arc welding workpiece.

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