Friction stir pretreatment method for aluminum alloy diffusion welding grain refinement surface

Abstract

The invention relates to a stirring friction pretreatment method for an aluminum alloy diffusion welding grain refinement surface, which comprises the following steps: starting from edge lines of a pair of to-be-welded surfaces of an aluminum alloy to-be-welded part, respectively carrying out multi-pass continuous equidistant stirring friction processing on the pair of to-be-welded surfaces, and ensuring that the translation overlapping rate of a stirring needle track between passes is 25-50%; during friction stir processing, water is continuously added for cooling, so that a spiral deformed fine grain layer with the grain size of 50-80 microns and the thickness of 1-2 mm is generated on a pair of to-be-welded surfaces at the position of a columnar stirring needle; and milling the pair of surfaces to be welded after the stirring friction processing is completed until the roughness is Ra 0.1-Ra 0.3, so as to obtain the aluminum alloy diffusion welding grain refinement surface. Compared with a welding seam obtained through a direct diffusion welding method, the welding seam obtained through the method has the higher welding rate and the higher strength, a new thought is provided for production and manufacturing of aluminum alloy, and the method has important significance in improving performance indexes and enhancing service reliability.

Description

Technical Field

[0001] The present invention relates to the field of welding technology. Background Art

[0002] Diffusion welding of aluminum alloy is an important manufacturing process for devices such as heat exchangers and 5G antennas, such as a microchannel structure heat exchanger manufactured by diffusion welding of 6063 aluminum alloy. Since microchannel heat exchangers usually have a complex microchannel structure with small dimensions, higher requirements for the amount of deformation are imposed during their manufacturing process. Diffusion welding is a precise and high-strength solid-phase welding technology, which better meets the urgent needs of forming precision complex structures and high-performance components. Therefore, it is expected to become the key to forming complex internal-channel aluminum alloy heat exchangers and even an irreplaceable technology.

[0003] However, due to the existence of a dense oxide film on the surface of aluminum alloy (Al2O3, with a melting point as high as 2054 °C) and the problem of secondary oxidation of the base material, during the diffusion welding process, a part of the oxide film is transformed into oxide particles and stably exists at the interface, hindering atomic diffusion and thus hindering the healing of interface pores, resulting in pores and weak connection defects that are difficult to eliminate at the interface.

[0004] As a surface modification technology, friction stir processing can produce a deformed fine-grained structure on the surface of aluminum alloy and introduce a relatively high distortion stored energy. These lattice distortion energies provide a driving force for atomic diffusion during the diffusion welding process, thereby promoting atomic diffusion, having a significant activation effect on the welding surface, and contributing to the healing of interface pores and the improvement of welding quality.

[0005] In the prior art, chemical cleaning or mechanical grinding is mostly used for the surface pretreatment method of aluminum alloy diffusion welding. However, these methods are difficult to completely eliminate the influence of the oxide film and cannot provide sufficient surface activation energy. Therefore, friction stir grain refinement on the surface is of great significance for improving the quality of aluminum alloy diffusion welding. Summary of the Invention

[0006] The purpose of the present invention is to avoid the deficiencies of the prior art and provide a friction stir pretreatment method for the surface of an aluminum alloy diffusion welding with a fine-grained surface obtained by friction stir processing, having a relatively large distortion stored energy, having an activation effect on a pair of surfaces to be welded, contributing to the healing of pores, and simultaneously increasing the welding rate and welding strength.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is: a friction stir pretreatment method for the surface of an aluminum alloy diffusion welding with grain refinement, including the following steps: A columnar stirring pin with a radius specification of 10 - 25 mm is used to start from the edge lines of a pair of welding surfaces of the aluminum alloy workpiece to be welded, and multi-pass and continuous equidistant friction stir processing is carried out on the pair of welding surfaces respectively. The translational overlap rate of the stirring pin trajectories between passes is 25% - 50%. Among them, the friction stir processing is carried out under the conditions of a rotational speed of 500 - 2500 rpm, a traveling speed of 65 - 300 mm / min, and a downward pressure of 1 - 10 mm. During the friction stir processing, the grains around the columnar stirring pin are deformed along the rotation direction of the columnar stirring pin, and it is promoted that the grain orientations are consistent at a distance of about 500 - 1000 μm from the pair of welding surfaces of the aluminum alloy in the thickness direction of the aluminum alloy workpiece to be welded, that is, a spiral structure is presented in the cross-section of the aluminum alloy workpiece to be welded. During the friction stir processing, water is continuously added to cool the pair of welding surfaces, so that the temperature of the pair of welding surfaces is maintained at 30 - 50 °C, so as to generate a spiral-shaped deformed fine grain layer with a grain size of 50 - 80 μm and a thickness of 1 - 2 mm on the pair of welding surfaces at the position of the columnar stirring pin. Among them, the spiral-shaped deformed fine grain layer has: a stored energy of distortion that provides power for atomic diffusion during the diffusion welding process, thereby promoting atomic diffusion and pore healing. At the same time, it also promotes the difference in the stored energy of distortion existing in the base material of the aluminum alloy diffusion welded part, so that the grain boundaries migrate, and thus has an activating effect on the pair of welding surfaces. Finally, the pair of welding surfaces after the friction stir processing is milled to a roughness of Ra 0.1 - Ra 0.3, and the grain-refined surface of the aluminum alloy diffusion welding is obtained. Among them, the roughness is used to ensure the quality of the diffusion welding.

[0008] Furthermore, it also includes that after the surface treatment before welding of the grain-refined surface of the aluminum alloy diffusion welding, furnace diffusion welding is carried out to obtain an aluminum alloy diffusion welded part with a grain-refined surface.

[0009] Furthermore, the surface treatment before welding is specifically as follows: First, the aluminum alloy diffusion welded part is cleaned with NaOH with a volume fraction of 8% - 12% for 70 - 75 s; Then it is cleaned with HNO3 with a volume fraction of 30% for 70 - 75 s, Finally, it is cleaned with anhydrous ethanol for 1 - 2 min and dried with a cold air blower.

[0010] Furthermore, the furnace diffusion welding is specifically as follows: The assembled welding tooling is placed in the diffusion welding furnace, evacuated, and the vacuum degree is maintained higher than 4 - 5×10 -2Pa, the aluminum alloy diffusion weldment is heated by radiation heating at a rate of 10±2℃ / min, and the temperature is raised to the welding temperature of 570±3℃ and then enters the insulation stage. The closed-loop pressurization system is turned on to perform diffusion welding on the aluminum alloy diffusion weldment at a welding pressure of 4±0.5MPa, and the temperature is kept for 90±5 min to improve the performance of the diffusion welding joint. After the diffusion welding is completed, it is cooled to room temperature at a cooling rate of 5±2℃ / min.

[0011] Furthermore, the friction stir process is performed at a rotation speed of 1000-1200 rpm, a travel speed of 98-102 mm / min, a downward pressure of 1-2 mm, and an overlap ratio of 25% between two passes; and then the surface is milled to a roughness of Ra 0.1-Ra 0.2.

[0012] Furthermore, the type of aluminum alloy is 6 series aluminum alloy.

[0013] Furthermore, the aluminum alloy diffusion weldment is a block weldment with a length and width of 50-100 mm and a thickness of 10-30 mm, and the welding surface area of ​​the weldment ranges from 2500 to 10000 mm. 2 .

[0014] Furthermore, the aluminum alloy is AA6061 or AA6063 aluminum alloy.

[0015] The beneficial effects of the present invention are as follows: compared with direct diffusion welding of aluminum alloy, the stir friction surface refined aluminum alloy has a larger distortion storage energy. These lattice distortion energies can provide power for atomic diffusion during the diffusion welding process, thereby promoting atomic diffusion, activating a pair of surfaces to be welded, and helping to bridge the holes.

[0016] Compared with the direct diffusion welding method, the weld obtained has a higher welding rate and higher strength. This provides a new idea for the production and manufacturing of aluminum alloys, which is of great significance for improving performance indicators and enhancing service reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the process of friction stir processing on the surface of an aluminum alloy sample of the present invention; Figure 2 This is a schematic diagram of the microstructure of the cross section of the aluminum alloy sample observed using an optical microscope after the friction stir processing of the present invention; Figure 3 This is a schematic diagram of sample clamping during welding process of specific example 1 of the present invention; Figure 4 This is a microstructure diagram of a diffusion welding joint of a specific example 1 of the present invention; Among them, (a-c) are the friction stir processed diffusion welding joint regions I, II, and III of the single-sided specimen, and (d-f) are the friction stir processed diffusion welding joint regions I, II, and III of the double-sided specimen; Figure 5 It is a comparison diagram of the room temperature tensile mechanical properties of the diffusion welding joint in Specific Example 1 of the present invention. Specific Embodiments

[0018] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0019] In order to achieve reliable connection of aluminum alloys and improve the mechanical properties of joints, the present invention uses the strong stirring action of the stirring head to cause severe plastic deformation, mixing, and fragmentation of the processed materials, realizing densification, homogenization, and refinement of the microstructure to produce fine grains and store lattice distortion energy. Therefore, deformed fine grains are generated on the surface of the specimen, with a large amount of distortion storage energy. These lattice distortion energies can provide power for atomic diffusion during the diffusion welding process, thereby promoting atomic diffusion, which is a possible way to solve the above problems.

[0020] For this reason, the present invention stirs and rubs a pair of surfaces to be welded of the base material to form a fine grain layer near the joint interface; due to a large amount of lattice distortion energy stored in these fine grains and the deformation of the grains, during the heat preservation process of diffusion welding, these deformed grains will gradually recrystallize, thus transforming from deformed grains to recrystallized grains. Finally, diffusion welding of aluminum alloys is realized by the method of diffusion welding, thereby improving the welding performance.

[0021] In order to achieve the above object, the present invention provides the following specific embodiments: Example 1: A friction stir pretreatment method for grain refinement on the surface of aluminum alloy diffusion welding, comprising the following steps: Step 1: Starting from the edge line of a pair of surfaces to be welded of the aluminum alloy workpiece, a columnar stirring pin with a radius specification of 10-25 mm is used to perform multi-pass and continuous equidistant friction stir processing on a pair of surfaces to be welded respectively, and the translation overlap rate of the stirring pin trajectories between passes is 25%-50%; Among them, the friction stir processing is carried out under the conditions of a rotational speed of 500-2500 rpm, a traveling speed of 65-300 mm / min, and a downward pressure of 1-10 mm; the grain orientations are consistent at a position about 500-1000 μm from a pair of surfaces to be welded of the aluminum alloy; During the friction stir processing, water is continuously added to cool a pair of surfaces to be welded, so that the temperature of a pair of surfaces to be welded is maintained at 30-50 °C, so as to generate a spiral deformed fine grain layer with a grain size of 50-80 μm and a thickness of 1-2 mm on a pair of surfaces to be welded at the position of the columnar stirring pin; Step 2: Milling the pair of surfaces to be welded after friction stir processing to a roughness of Ra 0.1 - Ra 0.3, thus obtaining the grain-refined surfaces for aluminum alloy diffusion welding. Step 3: First, cleaning the aluminum alloy diffusion welding parts with 8% - 12% (by volume) NaOH for 70 - 75 s; then cleaning with 30% (by volume) HNO3 for 70 - 75 s, finally, cleaning with absolute ethanol for 1 - 2 min and drying with a cold air blower; obtaining a pair of surfaces to be welded after pre-welding surface treatment; Step 4: Placing the assembled welding fixture into the diffusion welding furnace, evacuating to maintain a vacuum degree higher than 4 - 5×10 - 2 Pa, heating the aluminum alloy diffusion welding parts by radiation heating and increasing the temperature at a rate of 10 ± 2 °C / min. When the temperature rises to the welding temperature of 570 ± 3 °C, enter the heat preservation stage, turn on the closed-loop pressurization system, perform diffusion welding on the aluminum alloy diffusion welding parts with a welding pressure of 4 ± 0.5 MPa, and keep warm for 90 ± 5 min to improve the performance of the diffusion welding joint. After the diffusion welding is completed, cool to room temperature at a cooling rate of 5 ± 2 °C / min; thus obtaining the aluminum alloy diffusion welding parts with grain-refined surfaces.

[0022] Among them, the aluminum alloy type is 6-series aluminum alloy, and the aluminum alloy diffusion welding parts are block-shaped welding parts with a length and width of 50 - 100 mm and a thickness of 10 - 30 mm. The welding surface area range of the welding parts is 2500 - 10000 mm 2 .

[0023] Example 2 is the same as Example 1, except that during the friction stir, the friction stir processing is carried out at a rotational speed of 1000 - 1200 rpm, a traveling speed of 98 - 102 mm / min, and a downward pressure of 1 - 2 mm. The overlap ratio between two passes is 25%; then the surface is milled to a roughness of Ra 0.1 - Ra 0.2.

[0024] Example 3: The same as Example 1, except that: Using a columnar stirring pin with a radius specification of 10 mm, starting from the edge line of a pair of surfaces to be welded of the aluminum alloy welding parts, performing multi-pass and continuous equidistant friction stir processing on a pair of surfaces to be welded respectively. The translational overlap rate of the stirring pin trajectories between passes is 25%; Among them, the friction stir processing is carried out under the conditions of a rotational speed of 500 rpm, a traveling speed of 65 mm / min, and a downward pressure of 1 mm; the grain orientations are consistent at a distance of about 500 μm from a pair of surfaces to be welded of the aluminum alloy; During friction stir processing, continuously add water to cool a pair of surfaces to be welded, so that the temperature of the pair of surfaces to be welded is maintained at 30 °C, in order to generate a spiral-shaped deformed fine grain layer with a grain size of 50 μm and a thickness of 1 mm on the pair of surfaces to be welded at the position of the columnar stirring pin.

[0025] Example 4: The same as Example 1, except that a columnar stirring pin with a radius specification of 25 mm is used to perform multi-pass and continuous equidistant friction stir processing on a pair of surfaces to be welded of the aluminum alloy workpiece to be welded respectively, starting from the edge line of a pair of surfaces to be welded, and the translation overlap rate of the stirring pin trajectories between passes is 50%; Among them, the friction stir processing is carried out under the conditions of a rotational speed of 2500 rpm, a traveling speed of 300 mm / min, and a downward pressure of 10 mm; the grain orientations are consistent at a position about 1000 μm away from a pair of surfaces to be welded of the aluminum alloy; During friction stir processing, continuously add water to cool a pair of surfaces to be welded, so that the temperature of the pair of surfaces to be welded is maintained at 50 °C, in order to generate a spiral-shaped deformed fine grain layer with a grain size of 80 μm and a thickness of 2 mm on the pair of surfaces to be welded at the position of the columnar stirring pin. Example 5, the same as Example 1, except that: a columnar stirring pin with a radius specification of 18 mm is used to perform multi-pass and continuous equidistant friction stir processing on a pair of surfaces to be welded of the aluminum alloy workpiece to be welded respectively, starting from the edge line of a pair of surfaces to be welded, and the translation overlap rate of the stirring pin trajectories between passes is 35%; Among them, the friction stir processing is carried out under the conditions of a rotational speed of 1500 rpm, a traveling speed of 185 mm / min, and a downward pressure of 6 mm; the grain orientations are consistent at a position about 700 μm away from a pair of surfaces to be welded of the aluminum alloy; During friction stir processing, continuously add water to cool a pair of surfaces to be welded, so that the temperature of the pair of surfaces to be welded is maintained at 40 °C, in order to generate a spiral-shaped deformed fine grain layer with a grain size of 65 μm and a thickness of 1.8 mm on the pair of surfaces to be welded at the position of the columnar stirring pin.

[0026] Example 6, the same as Example 1, except that the aluminum alloy is AA6061 or AA6063 aluminum alloy.

[0027] To further illustrate the technical solutions and effects of the present invention, the following specific examples are provided: Specific Example 1: Taking AA6063 aluminum alloy and a block-shaped specimen with dimensions of 50×50×30 mm as the base material for diffusion welding as an example; First, insert the stirring pin into a pair of surfaces to be welded of the aluminum alloy for friction stir processing: A columnar stirring pin with a radius specification of 10 mm is used to perform multi-pass and continuous equidistant friction stir processing on a pair of weld surfaces of the aluminum alloy to-be-welded workpiece, starting from the edge lines of the pair of weld surfaces. The translation overlap rate of the stirring pin trajectories between passes is 25%; Among them, the friction stir processing is carried out under the conditions of a rotation speed of 1200 rpm, a traveling speed of 100 mm / min, and a downward pressure of 1 - 10 mm; the grain orientations are consistent at a position approximately 500 - 1000 μm away from the pair of weld surfaces of the aluminum alloy; During the friction stir processing, water is continuously added to cool the pair of weld surfaces to keep the temperature of the pair of weld surfaces at 30 °C, so as to generate a spiral-shaped deformed fine grain layer with a grain size of 70 μm and a thickness of 1.5 mm on the pair of weld surfaces at the position of the columnar stirring pin; Then, diffusion welding is carried out, and the welding temperature needs to consider the characteristics of the base material. In this specific example, the diffusion welding process used is as follows: The aluminum alloy AA6063 with a surface grain refinement for aluminum alloy diffusion welding is heated to 570 °C, and then a pressure of 4 MPa is applied and kept warm for 90 min to improve the joint performance.

[0028] As Figure 2 shown, Figure 2 That is, under the process parameters of a rotation speed of 1200 rpm and a feed speed of 100 mm / min, the aluminum alloy specimen shown in the figure is formed. Under the stirring action of the stirring pin, a fine grain layer with a grain size much smaller than the original grains is generated in the aluminum alloy base material at a position approximately 1500 μm away from the pair of weld surfaces. And the grain orientation regions are consistent at a position approximately 500 - 1000 μm away from the pair of weld surfaces, presenting a spiral shape.

[0029] This is because during the stirring process of the stirring pin, these grains are deformed along with the rotation direction of the stirring pin; thus, spiral lines are formed. These fine grain layers generated on the specimen surface are all deformed fine grains and have a large amount of stored distortion energy. This lattice distortion energy can provide power for atomic diffusion during the diffusion welding process to promote atomic diffusion, contribute to the closure of pores. At the same time, it is also hoped that the difference in the stored distortion energy of the two-side base materials causes the grain boundaries to migrate, so it has an activating effect on the pair of weld surfaces.

[0030] Figure 3 It is a schematic diagram of specimen clamping during the welding process. The aluminum alloy is subjected to diffusion welding in a vacuum environment. During the welding process, the specimen is clamped as shown in the figure. After rising to the welding temperature, pressure needs to be applied to make the material reach the yield state at this temperature, so that the welded materials first undergo plastic deformation, then creep, and finally atomic diffusion occurs, and the interface pores close.

[0031] Figure 4It is the recrystallized microstructure diagram of joints with one-sided friction stir welding and two-sided friction stir welding on the surface. Figure 4 (a-c) are one-sided friction stir welded joints. Figure 4 (d-f) are two-sided friction stir welded joints, that is, friction stir treatment of a pair of surfaces to be welded. Only a part of the grains of the base metal after one-sided surface friction stir treatment have completed recrystallization, and a certain proportion of deformed grains still remain.

[0032] Most of the base metal on the side without friction stir treatment before welding is recrystallized grains. There are still 11.6% of deformed grains in the joint of the one-sided friction stir treatment specimen, and only 46.9% of recrystallized grains. However, the recrystallized grains in the joint of the two-sided friction stir treatment specimen account for 99.8%. The joint of the two-sided friction stir treatment specimen completes recrystallization earlier than the joint of the one-sided friction stir treatment specimen.

[0033] Figure 5 It is the room temperature tensile mechanical properties of the joint after welding by the method proposed in the present invention. The performance of the joint with two-sided surface treatment is 85.6% of the strength of the base metal, which is 22.3% higher than the performance of the direct diffusion welded joint. The performance of the joint with one-sided surface friction stir welding is similar to that of the direct diffusion welded joint.

[0034] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A friction stir pretreatment method for grain refinement of the surface of diffusion welded aluminum alloy, characterized in that It includes the following steps: Starting from the edge lines of a pair of welding surfaces of the aluminum alloy workpiece to be welded, a columnar stirring pin with a radius specification of 10 - 25 mm is used to perform multi-pass and continuous equidistant friction stir processing on the pair of welding surfaces respectively, and the translational overlap rate of the stirring pin trajectories between passes is 25% - 50%; Among them, the friction stir processing is carried out under the conditions of a rotational speed of 500 - 2500 rpm, a traveling speed of 65 - 300 mm / min, and a downward pressure of 1 - 10 mm; During the friction stir processing, the grains around the columnar stirring pin are deformed along the rotation direction of the columnar stirring pin, and it is promoted that the grain orientations are consistent at a distance of about 500 - 1000 μm from the pair of welding surfaces of the aluminum alloy in the thickness direction of the aluminum alloy workpiece to be welded, that is, a spiral structure is presented in the cross-section of the aluminum alloy workpiece to be welded; During the friction stir processing, the pair of welding surfaces are continuously cooled with water to keep the temperature of the pair of welding surfaces at 30 - 50 °C, so as to generate a spiral deformed fine grain layer with a grain size of 50 - 80 μm and a thickness of 1 - 2 mm on the pair of welding surfaces at the position of the columnar stirring pin; Among them, the spiral deformed fine grain layer has: a stored distortion energy that provides power for atomic diffusion during the diffusion welding process, thereby promoting atomic diffusion and pore healing. At the same time, it also promotes the difference in the stored distortion energy existing in the base material of the aluminum alloy diffusion welded part, so that the grain boundaries migrate, and thus has an activation effect on the pair of welding surfaces; Finally, the pair of welding surfaces after the friction stir processing are milled to a roughness of Ra 0.1 - Ra 0.3, and the grain-refined surface of the aluminum alloy diffusion welding is obtained; Among them, the roughness is used to ensure the quality of the diffusion welding.

2. The friction stir pretreatment method for grain refinement on the surface of diffusion welded aluminum alloy as described in claim 1, characterized in that, It also includes: After the surface treatment before welding of the grain-refined surface of the aluminum alloy diffusion welding, furnace diffusion welding is carried out to obtain an aluminum alloy diffusion welded part with a grain-refined surface.

3. The friction stir pre-treatment method for grain refinement on the surface of diffusion-welded aluminum alloy according to claim 2, characterized in that, The surface treatment before welding mentioned above is specifically: First, the aluminum alloy diffusion welded part is cleaned with 8% - 12% NaOH by volume for 70 - 75 s; Then it is cleaned with 30% HNO3 by volume for 70 - 75 s, Finally, it is cleaned with anhydrous ethanol for 1 - 2 min and dried with a cold air blower.

4. The friction stir pretreatment method for grain refinement on the surface of diffusion welded aluminum alloy according to claim 2, characterized in that The furnace diffusion welding mentioned above is specifically: Put the assembled welding tooling into the diffusion welding furnace, evacuate the air, and maintain the vacuum degree higher than 4 - 5×10 -2 Pa. Heat the aluminum alloy diffusion welding parts by means of radiation heating, and increase the temperature at a rate of 10 ± 2℃ / min. When the temperature rises to the welding temperature of 570 ± 3℃, enter the heat preservation stage. Turn on the closed-loop pressurization system and perform diffusion welding on the aluminum alloy diffusion welding parts with a welding pressure of 4 ± 0.5MPa. Keep warm for 90 ± 5 min to improve the performance of the diffusion welding joint. After the diffusion welding is completed, cool it to room temperature at a cooling rate of 5 ± 2℃ / min.

5. The friction stir pretreatment method for grain refinement of the surface of diffusion-welded aluminum alloy as claimed in claim 1, characterized in that During the friction stir, the friction stir processing is carried out at a rotational speed of 1000 - 1200 rpm, a traveling speed of 98 - 102 mm / min, and a downward pressure of 1 - 2 mm, and the overlap ratio between two passes is 25%; then the surface is milled to a roughness of Ra 0.1 - Ra 0.

2.

6. The friction stir pre-treatment method for the surface of the grain-refined aluminum alloy diffusion welding according to any one of claims 1-5, characterized in that, The type of the aluminum alloy is 6-series aluminum alloy.

7. The friction stir pretreatment method for grain refinement of the surface of aluminum alloy diffusion welding according to any one of claims 1-5, characterized in that, The aluminum alloy diffusion weldment is a block weldment with a length and width of 50-100 mm and a thickness of 10-30 mm. The welding surface area of ​​the weldment ranges from 2500 to 10000 mm. 2 .

8. The friction stir pretreatment method for grain refinement on the surface of diffusion welded aluminum alloy as described in claim 6, characterized in that, The aluminum alloy is AA6061 or AA6063 aluminum alloy.

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