Friction stir welding partition gradient cooling device and gradient cooling method

Abstract

The application relates to a friction stir welding partition gradient cooling device, which comprises a cooling groove arranged in a supporting groove on a welding machine platform, a pad strip is used for dividing the cooling groove into a first cooling groove and a second cooling groove located on two sides of a weld seam, and the first cooling groove and the second cooling groove filled with cooling liquid are used for realizing gradient cooling in the thickness direction of the weld seam and gradient cooling in the length direction of a pair of weld plates when a stirring head is used for friction stir welding between two welding edges; meanwhile, the application also provides a cooling method of the cooling device. The application effectively improves the non-uniform heat cycle effect of materials in different areas of the weld seam in the friction stir welding process, and high-quality uniform friction stir welding can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of friction stir welding machine, in particular to a cooling method and device for friction stir welding. BACKGROUND

[0002] Friction stir welding is a solid-phase joining technique, in the welding process, the high-speed rotating tool and the workpiece are mechanically stirred and rubbed between them, forming friction heat, softening the material to a plastic state, and at the same time being extruded by the tool, so as to form a reliable joint in solid state. However, the material in the upper part of the weld seam subjected to mechanical stirring and friction of the large-size shoulder of the tool has a higher thermal coupling input, and the material in the bottom part of the weld seam subjected to the action of the relatively small-size pin experiences a lower thermal coupling input. The plastic softening degree of the material along the thickness direction of the plate is quite different, and the plasticized metal experiences different driving forces and appears abnormal flow, even forming "turbulent" phenomenon. At the same time, the cooling rate of the material in different regions of the weld seam along the thickness direction of the plate is different during the welding process. The heat conduction from the high-temperature zone to the low-temperature zone, the non-uniform thermal cycle caused by the difference in welding temperature and heat dissipation, and the abnormal tensile fracture in the weld nugget zone even occur in the bottom part. For aluminum alloy thick plate long weld friction stir welding, the whole workpiece is in a cold state at the initial stage, and as the welding process proceeds, the heat conduction from the high-temperature zone to the low-temperature zone, and the heat dissipation effect of the backing plate on the bottom of the long weld is continuously reduced as the temperature of the backing plate continuously rises. When the welding process reaches the subsequent workpiece subjected to preheating, the non-uniform thermal cycle caused by the difference in welding temperature and heat dissipation, and the difference in the initial state of the welding along the length direction of the long weld, the thermal cycle is quite different, resulting in a large difference in the microstructure and properties of the long weld along the length direction. SUMMARY

[0003] The present application aims to overcome the non-uniform thermal cycle of the material in different regions of the weld seam during the welding process, so that the high-temperature residence time of the weld seam will not be increased due to the preheating of the previous weld seam, and the mechanical properties of the uniform joint along the length direction and the thickness direction of the plate are uniformized, so that the present application can complete high-quality uniform welding.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: a friction stir welding partition gradient cooling device, comprising a support groove installed on a welding machine platform, a pair of workpieces fixed in the support groove, and a pair of workpiece edges opposite to each other and spliced to form a workpiece seam.

[0005] A cooling groove is provided in the support groove, and a spacer is provided in the cooling groove corresponding to the workpiece seam, which is used to combine with the two workpiece edges to form an overall friction stir welding base.

[0006] Meanwhile, the gasket divides the cooling groove into a first cooling groove and a second cooling groove located on both sides of the weld seam to be welded, and the first cooling groove and the second cooling groove filled with the cooling liquid are used to realize gradient cooling in the thickness direction of the weld seam and gradient cooling in the length direction of the pair of plates to be welded when the stirring head is used for friction stir welding between the two weld edges.

[0007] The cooling liquid circulation system is further used to dynamically adjust the filling flow rate of the cooling liquid near the starting position end of the friction stir welding and the outflow flow rate of the cooling liquid near the ending position end of the welding, so that the temperature of the outflowing cooling liquid is within the range of 30-60 DEG C, and the gradient cooling in the thickness direction of the weld seam and the gradient cooling in the length direction of the pair of plates to be welded are further ensured.

[0008] Further, the height of the first cooling groove and the second cooling groove is 8-30 mm, and the width is 20-100 mm; the height of the gasket is 8-30 mm, and the width is 10-200 mm.

[0009] The thickness of the plate to be welded is 3-50 mm, and the width is 80-300 mm.

[0010] The thickness of the plate to be welded is 3-50 mm, and the width is 80-300 mm.

[0011] Further, the diameter of the stirring head is 10-60 mm, and the width of the gasket is 10-200 mm, so as to ensure that the weld seam is not collapsed and the effective cooling of the first cooling groove and the second cooling groove to the plates to be welded on both sides of the weld seam is realized.

[0012] Further, the clamping tool for fixing the pair of plates to be welded in the support groove is further included, and the clamping tool includes a pressing block and an adjusting wedge.

[0013] The pressing block is arranged on both sides of the pair of plates to be welded, one end of the pressing block is fixed on the support groove, the other end of the pressing block is arranged on the pair of plates to be welded, and the pressing nut is fixed on the bottom of the support groove through the perforation of the pressing block, so as to press the end of the pressing block on the pair of plates to be welded.

[0014] The adjusting wedge is arranged on both sides of the pair of plates to be welded, and the wedge joint of the adjusting wedge is clamped between the pressing nut and the pair of plates to be welded, the inclined surface of the wedge joint is in contact with the pressing nut, and the supporting surface of the wedge joint is in contact with the pair of plates to be welded, so as to press the pair of plates to be welded and ensure the centering between the pair of plates to be welded and the stirring head.

[0015] Further, the pad strip is made of iron or copper or stainless steel or stone material; the pair of to-be-welded plates are 2XXX series or 7XXX series aluminum alloy rolling plates; and the support groove is made of die steel.

[0016] Further, the thermocouple is electrically connected to one end of the pair of to-be-welded plates, and the other end of the thermocouple is electrically connected to the temperature measuring system, which is used for detecting the temperature in the thickness direction of the to-be-welded seam under different cooling conditions, that is, measuring the gradient cooling effect in the thickness direction of the to-be-welded seam; at the same time, the thermal cycle in the length direction of the pair of to-be-welded plates and the heat dissipation detection of different regions, that is, measuring the gradient cooling effect in the length direction of the pair of to-be-welded plates.

[0017] The thermocouple is electrically connected to the connecting hole arranged on the pair of to-be-welded plates, the connecting hole is multiple, and the multiple connecting holes are arranged in pairs on the to-be-welded plates in the length direction of the pair of to-be-welded plates and the thickness direction of the to-be-welded seam, the arrangement direction of the connecting hole is perpendicular to the to-be-welded seam, the distance between two connecting holes in the length direction of the pair of to-be-welded plates is 100-300 mm, and the connecting holes are uniformly arranged in the thickness direction of the to-be-welded seam.

[0018] Further, the cooling liquid circulation system comprises a filling tank for storing cooling liquid, a first cooling tank and a second cooling tank, and a pipeline between the filling tank and the first cooling tank and the second cooling tank, and the filling tank fills the cooling liquid into the first cooling tank and the second cooling tank through the pump and the pipeline.

[0019] Further, the cooling liquid circulation system comprises a filling tank for storing cooling liquid, a first cooling tank and a second cooling tank, and a pipeline between the filling tank and the first cooling tank and the second cooling tank, and the filling tank fills the cooling liquid into the first cooling tank and the second cooling tank through the pump and the pipeline.

[0020] The temperature of the cooling liquid in the outflow pipeline is measured by a temperature table, and the filling amount and the outflow amount of the cooling liquid are dynamically adjusted through the filling tank, the pump and the outflow pipeline.

[0021] Further, the pair of to-be-welded plates are a pair of cuboid welding plates, the to-be-welded seam is the long side of the cuboid welding plate, and the size of the cuboid welding plate is 300-1500*80-500*3-50 mm.

[0022] The application also provides a gradient cooling method of the gradient cooling device for friction stir welding in the above-mentioned application, which comprises the following steps:

[0023] Step 1: mechanically polishing the pair of to-be-welded plates, and then cleaning the thermocouple temperature measuring connecting hole and the to-be-welded seam on the pair of to-be-welded plates with anhydrous ethanol;

[0024] Step 2: install the thermocouple, and select the stir head and pad strip according to the thickness of the pair of plates to be welded; fix the support groove on the welding machine platform, and fix the pair of plates to be welded on the support groove with the pressing block and adjusting wedge; adjust the centering between the pair of plates to be welded and the stir head, and linearly move the stir head to determine the starting position, ending position and welding length of the friction welding; Step 3: the cooling liquid circulation system fills the cooling liquid into the cooling tank through the pipeline, and waits for the first cooling tank and the second cooling tank to be filled with the cooling liquid;

[0025] Step 4: the stir head is used for friction stir welding at a rotating speed of 200-1000 rpm, a welding speed of 60-200 mm / min and a welding angle of 1.5-3.5°;

[0026] In the stir head penetration stage, the stir head is gradually penetrated at a feeding speed of 1-10 mm / min, the stir head shoulder contacts the opposite two welding edges of the pair of plates to be welded, that is, the penetration is completed, and then the friction stir welding is performed after being kept for 1-40 s, so that the non-plastic softened metal materials on the two welding edges form a stable flow of the inner extrusion plastic softened metal with the stir head;

[0027] During the friction stir welding, the amount of the stir head is adjusted to be 0.02-0.5 mm according to the flash and forming appearance of the surfaces of the pair of plates to be welded;

[0028] Step 5: after the welding is completed, when the test temperature of the thermocouple is below 100℃, the temperature measuring system is turned off, and the welded plates are disassembled.

[0029] Further, the cooling liquid in step 3 is filled into the first cooling tank and the second cooling tank, and then overflowed until the upper surfaces of the pair of plates to be welded are immersed, and the excess cooling liquid is discharged into the waste liquid tank through the discharge pipeline;

[0030] Before step 5, the temperature curves of the thermocouple connection points at different positions are collected by the temperature measuring system, which is used for studying the heat dissipation regulation in the gradient cooling of the first cooling tank and the second cooling tank corresponding to the length and thickness direction of the plates to be welded; wherein the heat dissipation refers to the convective heat exchange between the weld and the air, the heat conduction between the weld and the cold pad, the heat conduction between the bottom welding area of the weld and the cooling liquid in the cooling tank, and the heat conduction between the upper surface of the plate to be welded and the cooling liquid in the first cooling tank and the second cooling tank.

[0031] The present application has the advantages that: the present application provides a reliable and uniform partition gradient cooling method suitable for friction stir welding, which effectively improves the uneven heat cycle effect of the materials in different regions of the weld during the friction stir welding process, and finally proves the usability and reliability of the method provided by the present application through experiments, and high-quality uniform friction stir welding can be completed.

[0032] Specifically, the cooling method can effectively control the heat dissipation of different regions of the weld according to the needs, improve the large gradient heat cycle of the weld along the plate thickness direction and the high temperature residence time of different regions, so that the heat input of the subsequent to-be-welded part during welding is not increased due to the early heat conduction of the previous weld, and the different initial states caused by the temperature difference along the length direction are avoided, thereby improving the microstructure of the weak area of the weld, homogenizing the weld structure, reducing the difference in mechanical properties of the joint along the length direction and the plate thickness direction, and improving the mechanical properties.

[0033] Compared with the direct cooling of the iron backing plate, the peak temperature of the joint is reduced, the high temperature residence time is shortened, the temperature gradient is reduced, the minimum values of the overall joint yield strength, tensile strength and elongation after fracture are increased by 21.96%, 11.41% and 12.29% respectively, and the minimum values of the corresponding mechanical properties of the three equal division layered sections are increased by 17.57%, 13.35% and 6.37% respectively, and the mechanical property uniformity along the length direction of the welded plate and the thickness direction of the weld is obviously improved.

[0034] Under the optimized welding process parameters of the rotation speed of 400 rpm and the welding speed of 120 mm / min, the peak temperature of the submerged partition gradient cooling friction stir welding joint is further reduced, the high temperature residence time is further shortened, the temperature gradient is further reduced, the uniformity is obviously improved, the minimum values of the corresponding mechanical properties of the overall joint are increased by 28.08%, 19.74% and 40.41% respectively, the minimum values of the corresponding mechanical properties of the three equal division layered sections are increased by 21.72%, 16.58% and 41.40% respectively, the mechanical property uniformity along the length direction of the welded plate and the thickness direction of the weld is further obviously improved, and no abnormal fracture of the incomplete yield core zone occurs. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a schematic diagram of the friction stir welding structure of the present application;

[0036] In the figure, 1 is a support groove, 2 is a welding machine platform, 3 is a spacer, 4 is a pair of to-be-welded plates, 41 is a to-be-welded seam, 5 is a stir head, 6 is a cooling groove, 61 is a first cooling groove, 62 is a second cooling groove, 7 is a filling tank, 71 is a pump, 8 is a pipeline, 9 is an outflow pipeline, 10 is a waste liquid pool, 101 is a temperature table, 11 is a pressing block, 12 is a pressing nut, 13 is an adjusting wedge, 14 is a thermocouple, and 15 is a temperature measurement system.

[0037] Figure 2 It is a schematic diagram of the present application;

[0038] Figure 3 A schematic diagram of the profile cooling principle of the present application;

[0039] Figure 4 A schematic diagram of the whole cooling of the existing steel backing plate friction stir welding structure;

[0040] Figure 5 The temperature results of the high-strength aluminum alloy thick plate friction stir welded long weld prepared by specific examples 1, 2 and 3 of the present application;

[0041] Wherein, Figure 5 (a) is the whole cooling of the steel backing plate; Figure 5 (b) is the local cooling liquid partition gradient cooling of the lower surface; Figure 5 (c) is the local cooling liquid immersion partition gradient cooling of the lower surface;

[0042] Figure 6 The overall tensile properties along the length direction of the high-strength aluminum alloy thick plate friction stir welded long weld prepared by specific examples 1, 2 and 3 of the present application;

[0043] Wherein, Figure 6 (a) is the whole cooling of the steel backing plate; Figure 6 (b) is the local cooling liquid partition gradient cooling of the lower surface; Figure 6 (c) is the local cooling liquid immersion partition gradient cooling of the lower surface;

[0044] Figure 7 The tensile properties along the length direction of the layered sections of the high-strength aluminum alloy thick plate friction stir welded long weld prepared by specific examples 1, 2 and 3 of the present application;

[0045] Wherein, Figure 7 (a) is the whole cooling of the steel backing plate; Figure 7 (b) is the local cooling liquid partition gradient cooling of the lower surface; Figure 7 (c) is the local cooling liquid immersion partition gradient cooling of the lower surface;

[0046] Figure 8 The overall tensile fracture macroscopic morphology along the length direction of the high-strength aluminum alloy thick plate friction stir welded long weld prepared by specific examples 1, 2 and 3 of the present application;

[0047] Wherein, Figure 8 (a) is the whole cooling of the steel backing plate; Figure 8 (b) is the local cooling liquid partition gradient cooling of the lower surface; Figure 8 (c) is the local cooling liquid immersion partition gradient cooling of the lower surface;

[0048] Figure 9 The tensile fracture macroscopic morphology along the length direction of the layered sections of the high-strength aluminum alloy thick plate friction stir welded long weld prepared by specific examples 1, 2 and 3 of the present application;

[0049] wherein, Figure 9 (a) is overall cooling for steel backing plate; Figure 9 (b) is partial gradient cooling for lower surface by adding cooling liquid; Figure 9 (c) is partial gradient cooling for lower surface by adding cooling liquid immersion. DETAILED DESCRIPTION

[0050] The principles and features of the present application are described below in conjunction with the accompanying drawings, which are provided only for explanation of the present application and are not intended to limit the scope of the present application.

[0051] In the process of friction stir welding, the material in the region acted by the shoulder of the stir head experiences the highest peak temperature in the thermal cycle, and the material in the bottom of the weld seam acted by the relatively small pin experiences lower friction heat cycle, but the high temperature zone acted by the shoulder of the stir head conducts heat to the low temperature zone, and the material in the bottom of the weld seam experiences a long time of high temperature thermal cycle, especially in the heat affected zone. And for long weld seam friction stir welding of aluminum alloy, the whole to-be-welded plate is in a cold state in the initial stage, as the friction stir welding proceeds, the high temperature zone conducts heat to the low temperature zone which has not been welded, and the temperature of the backing plate continuously rises, which reduces the heat dissipation effect of the backing plate on the bottom of the long weld seam, and when welding to the subsequent to-be-welded material which has experienced preheating, the thermal cycle is uneven due to different welding temperatures and heat dissipation, which leads to different initial states of the long weld seam along the length direction, and there is a large difference in thermal cycle.

[0052] The present application is embodied by using the following main methods:

[0053] I. In the process of friction stir welding, the partition gradient cooling system is used to add cooling liquid, the heat dissipation in the welding process is controlled as needed from the back of the weld seam, the thermal cycle of the weak area of the weld seam is improved, and then the local microstructure is improved, so as to improve the local mechanical properties;

[0054] II. The partition gradient cooling device and method are used to add cooling liquid from the back of the weld seam until the whole to-be-welded part is completely immersed, which helps to reduce the peak temperature of each area of the weld seam along the thickness direction of the plate and shorten the high temperature residence time, uniformize the high-low temperature gradient, and improve the mechanical properties of the joint;

[0055] III. The partition gradient cooling device and method can reduce the heat conduction heating of the previous high temperature weld seam to the subsequent cold weld seam, reduce the initial temperature difference of the to-be-welded plate along the length direction, and reduce the high temperature residence time of the subsequent weld seam due to the preheating of the previous weld seam, uniformize the mechanical properties of the joint along the length direction, and further improve the overall performance of the joint.

[0056] In order to achieve the above purpose, the present application provides the following specific embodiments:

[0057] The embodiment 1 is shown in the figure, a kind of friction stir welding zoning gradient cooling device, including the support groove 1 being installed on the welding machine platform 2, a pair of to-be-welded plates 4 are fixed in support groove 1, and the opposite two welding edges of a pair of to-be-welded plates 4 are spliced to form to-be-welded seam 41. Figure 1 、 Figure 2 Wherein, a pair of to-be-welded plates 4 is a pair of cuboid welding plates, and to-be-welded seam 41 is the long side of cuboid welding plate, and the size of cuboid welding plate is 300-1500 × 80-500 × 3-50mm.

[0058] Cooling groove 6 is provided in support groove 1, and gasket 3 is padded in the cooling groove 6 corresponding to to-be-welded seam 41, to form the whole friction stir welding matrix with two welding edges.

[0059] Meanwhile, gasket 3 divides cooling groove 6 into first cooling groove 61 and second cooling groove 62 located on both sides of to-be-welded seam 41, and first cooling groove 61 and second cooling groove 62 filled with cooling liquid are used to realize gradient cooling in the thickness direction of to-be-welded seam 41 and gradient cooling in the length direction of a pair of to-be-welded plates 4 when friction stir welding head 5 is stirred between two welding edges.

[0060] Wherein, the height of first cooling groove 61 and second cooling groove 62 is 8-30mm, and the width is 20-100mm.

[0061] The height of gasket 3 is 8-30mm, and the width is 10-200mm.

[0062] The thickness of to-be-welded plate 4 is 3-50mm, and the width is 80-300mm,

[0063] To ensure the gradient cooling in the thickness direction of to-be-welded seam 41 and the gradient cooling effect in the length direction of a pair of to-be-welded plates 4.

[0064] The diameter of friction stir welding head 5 is 10-60mm, and the width of gasket 3 is 10-200mm, to ensure that to-be-welded seam 41 is not collapsed, and the effective cooling of first cooling groove 61 and second cooling groove 62 to the to-be-welded plates on both sides of to-be-welded seam 41 can be realized.

[0065] Further comprising cooling liquid circulating system respectively communicated with both ends of first cooling groove 61 and second cooling groove 62, which is used to dynamically adjust the filling flow of cooling liquid close to the starting position end of friction stir welding and the outflow flow of cooling liquid close to the ending position end of welding, so that the temperature of outflowing cooling liquid is in the range of 30-60℃, further ensuring the gradient cooling in the thickness direction of to-be-welded seam 41 and the gradient cooling in the length direction of a pair of to-be-welded plates 4.

[0066] Further comprising cooling liquid circulating system respectively communicated with both ends of first cooling groove 61 and second cooling groove 62, which is used to dynamically adjust the filling flow of cooling liquid close to the starting position end of friction stir welding and the outflow flow of cooling liquid close to the ending position end of welding, so that the temperature of outflowing cooling liquid is in the range of 30-60℃, further ensuring the gradient cooling in the thickness direction of to-be-welded seam 41 and the gradient cooling in the length direction of a pair of to-be-welded plates 4.

[0067] The cooling liquid circulation system comprises a filling tank 7 for storing cooling liquid, a first cooling tank 61 and a second cooling tank 62, and a pipeline 8 between the filling tank 7 and the first and second cooling tanks 61 and 62; the filling tank 7 fills the cooling liquid into the first and second cooling tanks 61 and 62 through the pump 71 and the pipeline 8;

[0068] The system further comprises an outflow pipeline 9, the first and second cooling tanks 61 and 62 are communicated with a waste liquid pool 10 through the outflow pipeline 9, the waste liquid pool 10 collects the cooling liquid flowing out of the outflow pipeline 9, and the excess cooling liquid flows into the waste liquid pool 10 through the outflow pipeline 9; the temperature of the cooling liquid in the outflow pipeline 9 is measured according to a temperature table 101, and the filling amount and the outflow amount of the cooling liquid are dynamically adjusted through the filling tank 7, the pump 71 and the outflow pipeline 9.

[0069] The system further comprises a clamping tool for fixing the pair of welding plates 4 in the support groove 1, and the clamping tool comprises a pressing block 11 and an adjusting wedge 13;

[0070] The pressing block 11 is arranged on both sides of the pair of welding plates 4, one end of the pressing block 11 is fixed on the support groove 1, the other end of the pressing block 11 is arranged on the pair of welding plates 4, and a pressing nut 12 is arranged on the bottom of the support groove 1 and penetrates the pressing block 11, so as to press the end of the pressing block 11 on the pair of welding plates 4;

[0071] The adjusting wedge 13 is arranged on both sides of the pair of welding plates 4, and the wedge joint of the adjusting wedge 13 is clamped between the pressing nut 12 and the pair of welding plates 4, the inclined surface of the wedge joint is in contact with the pressing nut 12, and the supporting surface of the wedge joint is in contact with the pair of welding plates 4, so as to press the pair of welding plates 4 and ensure the centering between the pair of welding plates 4 and the stirring head 5.

[0072] The pad strip 3 is made of iron, copper, stainless steel or stone; the pair of welding plates 4 is made of 2XXX or 7XXX aluminum alloy plate; and the support groove 1 is made of die steel.

[0073] In the embodiment 2, the same as the embodiment 1, the system further comprises a thermocouple 14 and a temperature measuring system 15, one end of the thermocouple 14 is electrically connected to the pair of welding plates 4, the other end of the thermocouple 14 is electrically connected to the temperature measuring system 15, so as to detect the temperature in the thickness direction of the welding seam 41 under different cooling conditions, that is, to measure the cooling effect in the thickness direction of the welding seam 41; at the same time, the thermal cycle in the length direction of the pair of welding plates 4 and the heat dissipation detection of different regions, that is, to measure the gradient cooling effect in the length direction of the pair of welding plates 4;

[0074] The thermocouple 14 is electrically connected in a pair of connecting holes 42 provided on the pair of welding plates 4. The connecting holes 42 are a plurality of connecting holes provided on the pair of welding plates 4 in the length direction of the pair of welding plates 4 and the thickness direction of the welding seam 41. The connecting holes 42 are provided in a direction perpendicular to the welding seam 41 and are uniformly provided in the length direction of the pair of welding plates 4 at a distance of 100-300 mm between every two connecting holes 42.

[0075] Embodiment 3: A gradient cooling method of the gradient cooling device for friction stir welding in embodiment 1, comprising the following steps:

[0076] Step 1: mechanically polishing the pair of welding plates 4, and then cleaning the thermocouple temperature measuring connecting holes 42 and the welding seam 41 on the pair of welding plates 4 with anhydrous ethanol;

[0077] Step 2: installing the thermocouple 14, and selecting the stir head 5 and the pad strip 3 according to the thickness of the pair of welding plates 4; fixing the support groove 1 on the welding machine platform 2, and fixing the pair of welding plates 4 on the support groove 1 with the pressing block 11 and the adjusting wedge 13; adjusting the centering between the pair of welding plates 4 and the stir head 5, and linearly moving the stir head 5 to determine the starting position, the ending position, and the welding length of the friction stir welding;

[0078] Step 3: the cooling liquid circulation system fills the cooling liquid into the cooling tank 6 through the pipeline 8, and waits until the first cooling tank 61 and the second cooling tank 62 are filled with the cooling liquid;

[0079] Step 4: the stir head 5 is used for friction stir welding at a rotating speed of 200-1000 rpm, a welding speed of 60-200 mm / min, and a welding angle of 1.5°-3.5°;

[0080] In the step, the stir head 5 is gradually fed at a feeding speed of 1-10 mm / min in the penetration stage, the shaft shoulder of the stir head 5 contacts the opposite two welding edges of the pair of welding plates 4, i.e., the penetration is completed, and then the friction stir welding is performed after maintaining for 1-40 s, so that the non-plastic softened metal material on the two welding edges and the plastic softened metal in the extrusion die formed by the stir head 5 stably flow;

[0081] In the friction stir welding, the flash and the forming appearance on the surface of the pair of welding plates 4 are observed, and the amount of pressing of the stir head 5 is adjusted to 0.02-0.5 mm;

[0082] Step 5: after the welding is completed, the temperature measuring system 15 is turned off when the test temperature of the thermocouple 14 is below 100℃, and the welded plates are disassembled.

[0083] Example 4: A gradient cooling method of the friction stir welding partition gradient cooling device of Example 1, the same as the steps of Example 3, except that:

[0084] After the cooling liquid is filled in the first cooling tank 61 and the second cooling tank 62 in step 3, it overflows until it immerses the upper surfaces of the pair of welding plates 4, and the excess cooling liquid enters the waste liquid pool 10 through the outflow pipeline 9;

[0085] Before step 5, it also includes collecting the temperature curves of the junctions of the thermocouples 14 at different positions by the temperature measurement system 15, for studying the heat dissipation regulation and control in the gradient cooling of the first cooling tank 61 and the second cooling tank 62 corresponding to the length and thickness directions of the welding plates on both sides of the welding seam 41;

[0086] The heat dissipation refers to the convective heat exchange between the welding seam 41 and the air, the heat conduction between the welding seam 41 and the cold pad 3, the heat conduction between the welding zone at the bottom of the welding seam 41 and the cooling liquid in the cooling tank 6, and the heat conduction between the upper surfaces of the welding plates 4 and the cooling liquid overflowing from the first cooling tank 61 and the second cooling tank 62 until it immerses the upper surfaces of the pair of welding plates 4.

[0087] To verify the effect of the present application, the following specific examples are provided, which are for the friction stir welding of 12.7mm thick 7050-T7451 aluminum alloy, using the same stir head and optimized welding process parameters, and completing three kinds of cooling respectively:

[0088] 1. The existing overall cooling of the steel pad, that is, without the cooling tank 6 structure, directly setting the steel pad 3 in the support groove 1 corresponding to the welding seam;

[0089] 2. The partition gradient cooling of the local cooling liquid on the lower surface of the heat-affected zone at the bottom of the welding plate, that is, filling the cooling liquid in the first cooling tank 61 and the second cooling tank 62 to achieve cooling;

[0090] 3. The partition gradient cooling of completely immersing the welding plate, that is, filling the first cooling tank 61 and the second cooling tank 62 until it immerses the upper surfaces of the pair of welding plates 4 to achieve cooling.

[0091] During the test welding process, the temperature curves of the characteristic points at different positions and the tensile properties after welding are taken to illustrate the technical effect of the present application, which will be described in detail in combination with specific examples and the accompanying drawings:

[0092] Specific Example 1:

[0093] (1) Cut the 12.7mm thick 7050-T7451 aluminum alloy rolling plate into 900x100x12.7mm block-shaped welding plates, and mechanically process the diameter 2.4mm holes for placing thermocouples at different positions along the length direction of the welding plate (30mm, 210mm, 370mm, 570mm, 730mm and 870mm from the starting end);

[0094] (2) Mechanically polish the welding position, clean the thermocouple temperature measurement hole and the welding position with anhydrous ethanol;

[0095] (3) Place the thermocouple for testing the temperature curve in the friction stir welding process, and fix it in the hole and connect it to the temperature measurement system;

[0096] (4) In the middle groove of the water cooling tank, mechanically fix the steel gasket with the same size as the groove on the support groove 1, that is, directly set the steel gasket 3 in the support groove 1 corresponding to the weld, without the cooling groove 6 structure;

[0097] (5) Mechanically fix the support groove 1 with the steel gasket on the friction stir welding machine platform, and adjust the centering between the horizontal and the stirring head;

[0098] (6) Mechanically fix the welding plate on the support groove 1 with the pressing plate, and use the triangular wedge to side-top, linearly move the stirring head, adjust the centering, obtain the welding starting position, ending position X, Y and Z three-dimensional coordinates, and the length needed to be welded;

[0099] (7) Set the welding process parameters: rotation speed 300rpm, welding speed 120mm / min, stirring head counterclockwise rotation, welding inclination angle 2.5°;

[0100] (8) According to the three-dimensional coordinates and welding length obtained in step (6), set the welding program, and perform friction stir welding. The stirring head penetration stage adopts gradual feeding, and the penetration is completed. After the penetration is completed, keep for 10s to make the extrusion die composed of the un-plastic softened metal material and the stirring head stable flow;

[0101] (9) The stirring head moves horizontally according to the set welding speed, and the down pressure is manually adjusted according to the flash and forming morphology of the surface during welding, and the temperature curve of the characteristic points at different positions is collected. At the same time, the heat dissipation is not controlled by using the zoning gradient cooling method during the welding process, and the heat dissipation is mainly the convective heat transfer with air and the heat conduction between the cold pad and the air;

[0102] (10) After welding, when the test temperature of the thermocouple is below 100℃, turn off the temperature measurement system, and disassemble the welding test plate.

[0103] According to the test characterization analysis, under the conditions of the rotation speed of 300 rpm and the welding speed of 60 mm / min, the whole iron backing plate of the 7050-T7451 aluminum alloy thick plate friction stir welded joint is well formed without obvious macro defects, and the joint has high strength and toughness. The temperature curves of the characteristic points at different positions along the length direction of the obtained welded joint are shown in Figure 5 (a). The tensile properties of the whole joint and the three-layered sections along the plate thickness direction are shown in Figure 6 (a) and Figure 7 (a), respectively.

[0104] As shown in Figure 8 (a), the tensile failure mainly occurs in the 45° shear ductile fracture in the heat affected zone of the welded joint, and part of the failure occurs in the heat affected zone close to the weld nugget zone.

[0105] The average yield strength, tensile strength and elongation after fracture of the upper part of the joint along the plate thickness direction are 278±17.17 MPa, 392±7.30 MPa and 4.66±0.58%, respectively, the maximum values are 324 MPa, 403 MPa and 6.08%, respectively, and the minimum values are 260 MPa, 378 MPa and 3.97%, respectively. The average yield strength, tensile strength and elongation after fracture of the middle section are 286±26.28 MPa, 402±25.07 MPa and 5.22±1.03%, respectively, the maximum values are 342 MPa, 467 MPa and 8.74%, respectively, and the minimum values are 266 MPa, 381 MPa and 3.62%, respectively. The average yield strength, tensile strength and elongation after fracture of the bottom section are 266±26.14 MPa, 391±26.44 MPa and 5.46±0.68%, respectively, the maximum values are 343 MPa, 461 MPa and 6.52%, respectively, and the minimum values are 249 MPa, 366 MPa and 3.14%, respectively. The minimum yield strength, tensile strength and elongation after fracture of the three-layered sections of the iron backing plate friction stir welded joint are 249 MPa, 366 MPa and 3.14%, respectively. As shown in Figure 9 (a), the tensile failure mainly occurs in the 45° shear ductile fracture in the heat affected zone of the welded joint, and part of the failure occurs in the heat affected zone close to the weld nugget zone.

[0106] Specific Example 2:

[0107] (1) Cut the 12.7mm thick 7050-T7451 aluminum alloy rolling plate into 900x100x12.7mm block-shaped to-be-welded plates, and mechanically process the diameter 2.4mm holes for placing thermocouples at different positions along the length direction of the to-be-welded plates (30mm, 210mm, 370mm, 570mm, 730mm and 870mm from the starting end respectively);

[0108] (2) Mechanically polish the to-be-welded parts, and clean the to-be-welded parts and the holes for placing thermocouples for temperature measurement with anhydrous ethanol;

[0109] (3) Place the thermocouples for testing the temperature curve in the friction stir welding process, and mechanically fix the holes and connect to the temperature measurement system;

[0110] (4) According to the thickness of the to-be-welded plate and the size of the selected stir head, select the appropriate spacer, and mechanically fix the selected steel spacer in the middle groove of the water cooling tank body;

[0111] (5) Mechanically fix the support groove 1 with steel spacers and symmetrical cooling grooves on both sides on the friction stir welding machine platform, and adjust the centering between the horizontal and the stir head;

[0112] (6) Mechanically fix the to-be-welded plate on the water cooling tank body with a pressing plate, and side-top with a triangular wedge, linearly move, adjust the centering, obtain the three-dimensional coordinates of the welding starting position, ending position X, Y and Z, and the length needed to be welded;

[0113] (7) Fill the cooling liquid from the injection hole by using the cooling liquid circulation system, fill the cooling liquid in the first cooling groove and the second cooling groove between the tank body and the spacer on both sides, manually control the flow to the cooling liquid not to overflow the bottom cooling groove, and the cooling liquid flows out from the outflow hole and enters the waste liquid pool;

[0114] (8) Set the welding process parameters: rotation speed 300rpm, welding speed 120mm / min, the stir head rotates counterclockwise, and the welding inclination angle is 2.5°;

[0115] (9) Set the welding program according to the three-dimensional coordinates and the welding length obtained in step (6), and perform friction stir welding. The gradual feeding is adopted in the stir head penetration stage, the penetration of the stir head is completed, and after the penetration is completed, 10s is maintained to make the extrusion die composed of the un-plastic softened metal material and the stir head stable flow;

[0116] (10) The stirring head moves horizontally at the set welding speed. The amount of depression is adjusted manually according to the flash and forming morphology of the surface during welding, and the temperature curves of the characteristic points at different positions are collected. At the same time, a partition gradient cooling method is used for heat dissipation control during welding. The heat dissipation mainly includes convective heat transfer with air, heat conduction between the cold steel pad and the weld seam, and heat conduction between the weld seam bottom heat affected zone and the cooling liquid in the cooling tank;

[0117] (11) After welding, when the test temperature of the thermocouple drops below 100°C, the temperature measurement system is turned off, and the welded test plate is disassembled.

[0118] According to the test characterization analysis, under the conditions of a rotation speed of 300 rpm and a welding speed of 60 mm / min, the 7050-T7451 aluminum alloy thick plate lower surface local cooling liquid partition gradient cooling friction stir welding seam forms well without obvious macroscopic defects, and the joint toughness is high. The temperature curves of the weld seam at different positions along the length direction are as shown in Figure 5 (b), the tensile properties of the joint as a whole and the three equal parts along the thickness direction are as shown in Figure 6 (b) and Figure 7 (b), it can be seen that compared with the same position characteristic points of the steel pad overall cooling friction stir welding seam in specific example 1, the peak temperature of the lower surface local cooling liquid partition gradient cooling welding seam is reduced, the high temperature residence time is shortened, and the temperature gradient of different regions is reduced.

[0119] The average values of the joint as a whole along the length direction are 325±8.80 MPa, 458±6.74 MPa and 6.85±0.35%, respectively, and the maximum values are 336 MPa, 466 MPa and 7.57%, respectively, and the minimum values are 308 MPa, 435 MPa and 6.03%, respectively. As shown in Figure 5 (b), the tensile failure mainly occurs in the 45° shear toughness fracture in the weld heat affected zone, and part of the fracture occurs in the thermal influence zone near the weld nugget zone. Compared with the iron pad direct cooling joint, the minimum values of the yield strength, tensile strength and elongation of the lower surface local cooling liquid partition gradient cooling friction stir welded joint are increased by 21.96%, 11.41% and 12.29%, respectively. As shown in Figure 8 (b), the tensile failure mainly occurs in the 45° shear toughness fracture in the weld heat affected zone.

[0120] The average values of the upper yield strength, tensile strength and elongation after fracture of the joint sliced along the thickness direction of the plate are 320 ± 10.77 MPa, 438 ± 11.82 MPa and 5.66 ± 0.62%, respectively, the maximum values are 342 MPa, 457 MPa and 6.47%, respectively, and the minimum values are 293 MPa, 415 MPa and 3.85%, respectively. The average values of the yield strength, tensile strength and elongation after fracture of the middle slice are 335 ± 7.07 MPa, 454 ± 9.85 MPa and 5.31 ± 0.55%, respectively, the maximum values are 343 MPa, 468 MPa and 5.98%, respectively, and the minimum values are 320 MPa, 432 MPa and 3.34%, respectively. The average values of the yield strength, tensile strength and elongation after fracture of the bottom slice are 347 ± 13.43 MPa, 461 ± 8.22 MPa and 5.15 ± 0.23%, respectively, the maximum values are 368 MPa, 471 MPa and 5.59%, respectively, and the minimum values are 320 MPa, 443 MPa and 4.56%, respectively. The minimum values of the yield strength, tensile strength and elongation after fracture of the three-equal-section sliced joint of the 7050-T7451 aluminum alloy thick plate with local cooling liquid partition gradient cooling at the lower surface are 293 MPa, 415 MPa and 3.34%, respectively, which are 17.57%, 13.35% and 6.37% higher than the minimum values of 249 MPa, 366 MPa and 3.14% of the three-equal-section sliced joint of the 7050-T7451 aluminum alloy thick plate with overall cooling friction stir welding. As shown in FIG. 6, Figure 9 (b) shows that the tensile failure mainly occurs in the 45° shear toughness fracture of the weld heat-affected zone.

[0121] Under the conditions of a rotation speed of 300 rpm and a welding speed of 120 mm / min, the mechanical property uniformity of the 7050-T7451 aluminum alloy thick plate joint with local cooling liquid partition gradient cooling at the lower surface along the length direction and the thickness direction is obviously improved compared with that obtained in specific example 1.

[0122] Specific example 3:

[0123] (1) Cut a 12.7 mm thick 7050-T7451 aluminum alloy rolling plate into a 900 × 100 × 12.7 mm block-shaped to-be-welded plate, and mechanically process a 2.4 mm diameter hole for placing a thermocouple at different positions (30 mm, 210 mm, 370 mm, 570 mm, 730 mm and 870 mm from the starting end) along the length direction of the to-be-welded plate for temperature measurement;

[0124] (2) Mechanically polish the to-be-welded part, and clean the hole for placing the thermocouple for temperature measurement and the to-be-welded part with anhydrous ethanol;

[0125] (3) Place the thermocouple for testing the temperature curve during the friction stir welding process, and fix it in the hole and connect it to the temperature measurement system;

[0126] (4) According to the thickness of the to-be-welded plate and the size of the selected stir head, select a suitable shim and mechanically fix the selected steel shim at the middle groove of the water-cooled tank body;

[0127] (5) Mechanically fix the tank body with the steel shim and the symmetrically distributed cooling grooves on both sides on the friction stir welding machine platform, and adjust the centering between the horizontal and the stir head;

[0128] (6) Mechanically fix the to-be-welded plate on the water-cooled tank body with a pressing plate, and side-top with a triangular wedge. Linearly move the stir head, adjust the centering, obtain the three-dimensional coordinates of the welding starting position, ending position X, Y and Z, and the length of the welding required;

[0129] (7) Fill the cooling liquid from the injection hole by using the cooling liquid circulation system, fill the cooling liquid in the symmetrically distributed cooling grooves between the tank body and the shim on both sides until it just submerges the upper surface of the to-be-welded plate, and then overflow until it just submerges the upper surface of the to-be-welded plate. The cooling liquid flows out from the outflow hole and enters the waste liquid pool;

[0130] (8) Set the welding process parameters: rotation speed 300 rpm, welding speed 120 mm / min, stir head counterclockwise rotation, and welding inclination angle 2.5°;

[0131] (9) Set the welding program according to the three-dimensional coordinates and the welding length obtained in step (6), and perform friction stir welding. The gradual feeding is adopted in the stir head penetration stage, and the penetration of the stir head is completed. After the penetration is completed, it is kept for 10 s to make the plastic softened metal in the extrusion die composed of the un-plastic softened metal and the stir head flow stably;

[0132] (10) The stir head moves horizontally according to the set welding speed. During the welding, the amount of depression is adjusted manually according to the surface flash and the forming morphology, and the temperature curve of the characteristic points at different positions is collected. At the same time, the heat dissipation is controlled by using the zoning gradient cooling method during the welding process. The heat dissipation mainly includes convective heat transfer with air, heat conduction between the cold steel shim, heat conduction between the heat-affected zone at the bottom of the weld and the cooling liquid in the cooling groove, and heat conduction between the upper surface of the weld and the stir head and the cooling liquid;

[0133] (11) After the welding is completed, when the test temperature of the thermocouple drops below 100℃, the temperature measurement system is turned off, and the welded test plate is disassembled.

[0134] According to the test and characterization analysis, under the conditions of rotation speed 400 rpm and welding speed 120 mm / min, the 7050-T7451 aluminum alloy thick plate local cooling liquid immersion zoning gradient cooling friction stir welded joint is well formed without obvious macroscopic defects, and the joint has high strength and toughness. The temperature curve of the weld at different positions along the length direction is as follows: Figure 5As shown in (c), the tensile properties of the joint as a whole and the three equally divided slices along the thickness direction along the length direction are as follows: Figure 6 (c) and Figure 7 As shown in (c), it can be seen that compared with the same feature points of the steel pad plate integral cooling friction stir weld in specific example 1, the peak temperature of the localized gradient cooling weld with coolant immersion on the lower surface is further reduced, the high temperature dwell time is shorter, the temperature gradient in different areas is further reduced, and it is more uniform.

[0135] The average yield strength, tensile strength, and elongation after fracture of the joint along its length were 336±7.01 MPa, 472±2.56 MPa, and 8.50±0.51%, respectively; the maximum values ​​were 348 MPa, 476 MPa, and 9.41%, respectively; and the minimum values ​​were 323 MPa, 468 MPa, and 7.54%, respectively. Figure 5 As shown in (b), all tensile failures occurred at 45° shear toughness in the heat-affected zone of the weld. For friction stir welded joints with localized surface immersion in coolant and gradient cooling at a rotation speed of 400 rpm and a welding speed of 120 mm / min, compared to joints with direct cooling by a backing plate at a rotation speed of 300 rpm and a welding speed of 60 mm / min, the overall yield strength, tensile strength, and minimum elongation after fracture were increased by 28.08%, 19.74%, and 40.41%, respectively. Figure 8 As shown in (c), tensile failure mainly occurs in the heat-affected zone of the weld at 45° shear toughness fracture, and no abnormal fracture occurs in the weld nugget zone where the weld is not fully yielded.

[0136] The average values of the upper yield strength, tensile strength and elongation after fracture of the joint along the thickness direction of the plate are 337 ± 15.19 MPa, 457 ± 14.63 MPa and 6.38 ± 0.77%, respectively, the maximum values are 361 MPa, 476 MPa and 7.95%, respectively, and the minimum values are 304 MPa, 427 MPa and 4.56%, respectively. The average values of the yield strength, tensile strength and elongation after fracture of the middle section are 354 ± 9.10 MPa, 477 ± 9.63 MPa and 6.41 ± 0.53%, respectively, the maximum values are 374 MPa, 487 MPa and 6.97%, respectively, and the minimum values are 329 MPa, 442 MPa and 4.44%, respectively. The average values of the yield strength, tensile strength and elongation after fracture of the bottom section are 349 ± 13.26 MPa, 478 ± 12.01 MPa and 6.54 ± 0.35%, respectively, the maximum values are 363 MPa, 489 MPa and 7.27%, respectively, and the minimum values are 303 MPa, 434 MPa and 5.94%, respectively. The minimum values of the yield strength, tensile strength and elongation after fracture of the three-equal-section layered sections of the joint with local cooling liquid immersion zoning gradient cooling at the lower surface are 329 MPa, 442 MPa and 5.94%, respectively, which are 21.72%, 16.85% and 41.40% higher than the minimum values of 303 MPa, 427 MPa and 4.44%, respectively, of the three-equal-section layered sections of the joint with overall cooling by the iron backing plate. As shown in FIG. 8, Figure 9 (c) shows that the tensile failure mainly occurs in the 45° shear toughness fracture of the weld heat-affected zone, and no incomplete yield abnormal fracture of the nugget zone occurs.

[0137] Under the conditions of a rotation speed of 400 rpm and a welding speed of 120 mm / min, the uniformity of the mechanical properties of the 7050-T7451 aluminum alloy thick plate joint with local cooling liquid immersion zoning gradient cooling at the lower surface is further obviously improved along the length direction and the thickness direction compared with the specific examples 1 and 2.

[0138] The above only describes the preferred specific examples of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A friction stir welding zonal gradient cooling device, characterized by, The application relates to a welding device for a pair of plates, which comprises a support groove (1) installed on a welding machine platform (2), a pair of plates to be welded (4) fixed in the support groove (1), and a pair of welding edges of the plates to be welded (4) jointed to form a welding seam (41); a cooling groove (6) is arranged in the support groove (1), and a gasket (3) is arranged in the cooling groove (6) corresponding to the welding seam (41) and used for combining with the two welding edges to form an integral friction stir welding base; Meanwhile, the gasket (3) divides the cooling groove (6) into a first cooling groove (61) and a second cooling groove (62) located on the two sides of the welding seam (41), the first cooling groove (61) and the second cooling groove (62) filled with cooling liquid are used for realizing gradient cooling in the thickness direction of the welding seam (41) and gradient cooling in the length direction of the pair of plates to be welded (4) when a stirring head (5) is used for friction stir welding between the two welding edges; The application further comprises a cooling liquid circulating system communicated with the two ends of the first cooling groove (61) and the second cooling groove (62) respectively, the cooling liquid circulating system is used for dynamically adjusting the filling flow of the cooling liquid close to the starting position end of the friction stir welding and the outflow of the cooling liquid close to the ending position end of the welding, so that the temperature of the outflowing cooling liquid is in the range of 30-60 DEG C, and the gradient cooling in the thickness direction of the welding seam (41) and the gradient cooling in the length direction of the pair of plates to be welded (4) are further ensured; The application further comprises a clamping tool used for fixing the pair of plates to be welded (4) in the support groove (1), and the clamping tool comprises a pressing block (11) and an adjusting wedge block (13); The pressing block (11) is arranged on the two sides of the pair of plates to be welded (4), one end of the pressing block (11) is fixed on the support groove (1), the other end of the pressing block (11) is arranged on the pair of plates to be welded (4), a pressing nut (12) is fixed on the bottom of the support groove (1) through a through hole of the pressing block (11), and the end of the pressing block (11) is pressed on the pair of plates to be welded (4); The adjusting wedge block (13) is arranged on the two sides of the pair of plates to be welded (4), and a wedge joint of the adjusting wedge block (13) is clamped between the pressing nut (12) and the pair of plates to be welded (4), an inclined surface of the wedge joint is matched with the pressing nut (12), a supporting surface of the wedge joint is matched with the pair of plates to be welded (4), and the adjusting wedge block (13) is used for pressing the pair of plates to be welded (4) and ensuring the centering between the pair of plates to be welded (4) and the stirring head (5); The cooling liquid circulating system comprises a filling tank (7) used for storing the cooling liquid and pipelines (8) between the filling tank (7) and the first cooling groove (61) and the second cooling groove (62), and the filling tank (7) fills the cooling liquid into the first cooling groove (61) and the second cooling groove (62) through a pump (71) and the pipelines (8). ​ It also includes the outflow pipeline (9), the first cooling tank (61) and the second cooling tank (62) are communicated by the outflow pipeline (9) with the waste liquid pool (10), the waste liquid pool (10) collects the cooling liquid flowed out by the outflow pipeline (9), for making the excess cooling liquid enter the waste liquid pool (10) through the outflow pipeline (9); The temperature of the cooling liquid in the outflow pipeline (9) is measured according to the temperature table (101), and the filling amount and the outflow amount of the cooling liquid are dynamically controlled through the filling tank (7), the pump (71) and the outflow pipeline (9); It also includes a thermocouple (14) and a temperature measurement system (15), one end of the thermocouple (14) is electrically connected to a pair of welding plates (4), the other end of the thermocouple (14) is electrically connected to the temperature measurement system (15), which is used for detecting the temperature in the thickness direction of the weld (41) under different cooling conditions, that is, measuring the gradient cooling effect in the thickness direction of the weld (41); At the same time, the thermal cycle and heat dissipation detection of the length direction of the pair of welding plates (4) and different regions, that is, measuring the gradient cooling effect in the length direction of the pair of welding plates (4); The thermocouple (14) is electrically connected in the connecting hole provided on the pair of welding plates (4), the connecting hole (42) is a plurality of connecting holes, which are provided on the pair of welding plates (4) in the length direction and the thickness direction of the weld (41), the connecting hole (42) is perpendicular to the weld (41), and the distance between the two connecting holes (42) in the length direction of the pair of welding plates (4) is 100-300mm, and the connecting holes (42) are uniformly arranged in the thickness direction of the weld (41); It also includes a gradient cooling method realized by the gradient cooling device for friction stir welding, which comprises the following steps: Step 1: mechanically polishing a pair of welding plates (4), then cleaning the thermocouple temperature measuring connecting hole (42) and the weld (41) on the pair of welding plates (4) with anhydrous ethanol; Step 2: install the thermocouple (14), and select the stir head (5) and the pad strip (3) according to the thickness of the pair of welding plates (4); fix the support groove (1) on the welding machine platform (2), and fix the pair of welding plates (4) on the support groove (1) with the pressing block (11) and the adjusting wedge (13); adjust the centering between the pair of welding plates (4) and the stir head (5), and linearly move the stir head (5) to determine the starting position, the ending position and the welding length of the friction stir welding; Step 3: the cooling liquid circulation system fills the cooling liquid into the cooling tank (6) through the pipeline (8), and the first cooling tank (61) and the second cooling tank (62) are filled with the cooling liquid; The cooling liquid in step 3 is filled into the first cooling tank (61) and the second cooling tank (62) and overflowed until the upper surface of the pair of welding plates (4) is immersed, and the excess cooling liquid enters the waste liquid pool (10) through the outflow pipeline (9); Step 4: the stir head (5) is used for friction stir welding at a rotating speed of 200-1000 rpm, a welding speed of 60-200 mm / min and a welding angle of 1.5°-3.5°. Wherein, the stirring head (5) is gradually fed into the stage with a feeding speed of 1~10 mm / min, the stirring head (5) contacts the opposite two welding edges of a pair of plates to be welded (4) and is fed in, then keeps for 1~40 s and then performs friction stir welding, so that the non-plastic softened metal material on the two welding edges and the stirring head (5) form a stable flow of plastic softened metal in the extrusion die; During the friction stir welding, the amount of pressing of the stirring head (5) is adjusted to be 0.02~0.5 mm according to the flash and forming appearance of the surface of the pair of plates to be welded (4); Step 5: After the welding is completed, when the test temperature of the thermocouple (14) drops to below 100 ℃, the temperature measuring system (15) is turned off, and the welded plate is disassembled; At the same time, before step 5, the temperature curve of the connection point of the thermocouple (14) at different positions is collected by the temperature measuring system (15), which is used to study the heat dissipation regulation and control in the gradient cooling of the first cooling groove (61) and the second cooling groove (62) corresponding to the length and thickness direction of the plates to be welded. Wherein, the heat dissipation refers to the convective heat exchange between the weld (41) and the air, the heat conduction between the weld (41) and the cold pad (3), the heat conduction between the bottom welding area of the weld (41) and the cooling liquid in the cooling groove (6), and the heat conduction between the upper surface of the weld (41) and the stirring head (5) and the cooling liquid in the first cooling groove (61) and the second cooling groove (62).

2. The zoned gradient cooling apparatus for friction stir welding of claim 1, wherein, The height of the first cooling groove (61) and the second cooling groove (62) is 8~30 mm, and the width is 20~100 mm. The height of the pad (3) is 8~30 mm, and the width is 10~200 mm. The thickness of the plate to be welded (4) is 3~50 mm, and the width is 80~300 mm, To ensure the gradient cooling effect in the thickness direction of the weld (41) and the gradient cooling effect in the length direction of the pair of plates to be welded (4).

3. The zoned gradient cooling apparatus of claim 1, wherein, The diameter of the stirring head (5) is 10~60 mm, and the width of the pad (3) is 10~200 mm, so as to ensure that the weld (41) is not collapsed and the first cooling groove (61) and the second cooling groove (62) can effectively cool the plates to be welded on both sides of the weld (41).

4. The zoned gradient cooling apparatus of claim 1, wherein, The pad (3) is made of iron, copper, stainless steel or stone; the pair of plates to be welded (4) is a 2XXX series or 7XXX series aluminum alloy plate; and the support groove (1) is made of die steel.

5. The zoned gradient cooling apparatus for friction stir welding of any one of claims 1-4, wherein, The pair of plates to be welded (4) is a pair of rectangular plates, the weld (41) is the long side of the rectangular plate, and the size of the rectangular plate is 300~1500×80~500×3~50 mm.

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