Method for treating high-volume-fraction particle reinforced aluminum-based surface through friction stir

Abstract

The invention belongs to the technical field of metal-based composite material preparation, and particularly relates to a method for treating a high-volume-fraction particle reinforced aluminum-based surface through friction stir. In order to solve the problems of particle aggregation, uneven distribution and the like in the preparation process of a high-volume-fraction particle reinforced aluminum-based composite material in the prior art, the invention innovatively introduces a method for mixing and adding solid lubricating particles with two-dimensional layered structures and hard particles. According to the method, the interface regulation and control effect of the two-dimensional layered particles is used in cooperation with the special stirring head, uniform distribution of the hard particles in the composite layer is effectively promoted, the hole defect caused by particle aggregation is remarkably reduced, and controllable preparation of the high-volume-fraction particle reinforced aluminum matrix composite is achieved. And subsequent solid solution and aging heat treatment are combined, so that the comprehensive mechanical property and wear resistance of the material are further improved. The method is simple in process and easy to implement, and has good engineering application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of metal matrix composites, and particularly relates to a method for using friction stir processing to enhance the surface of aluminum matrix with high volume fraction of particles. Background Art

[0002] Aluminum matrix composites have been widely used in aerospace, automotive and other fields due to their low density, high specific strength, good thermal conductivity and anti-wear performance. As a solid-state processing technology, friction stir processing has the characteristics of low energy consumption and environmental friendliness, and has become one of the important methods for preparing metal matrix composites. At present, there are still many technical bottlenecks in the preparation of high volume fraction particle-reinforced aluminum matrix composites, which are mainly manifested in: during the process, the reinforcing phase particles are prone to agglomeration and uneven distribution, seriously affecting the comprehensive performance of the material; the traditional mechanical stirring method is difficult to achieve uniform dispersion of particles under high volume fraction conditions; the interface bonding between particles and matrix is poor, reducing the overall performance of the material; during the friction stir processing, due to the high particle content, the tool wear is serious, affecting the processing efficiency and quality. Therefore, developing a new preparation process to achieve uniform distribution of high volume fraction particles and improve the comprehensive performance of composites has important theoretical significance and engineering application value. Summary of the Invention

[0003] Aiming at the above problems, the purpose of the present invention is to use the friction stir processing method to solve the technical problems in the preparation process of high volume fraction particle-reinforced aluminum matrix composites by introducing two-dimensional layered solid lubricant particles and using a special stirring head. The method for using friction stir processing to enhance the surface of aluminum matrix with high volume fraction of particles according to the present invention includes the following steps:

[0004] (1) Preparing a reinforcing phase with a high volume fraction: a mixed particle composed of hard particles and lubricant particles is used as the reinforcing phase. The hard particles and lubricant particles in the reinforcing phase are mixed at a volume ratio of (65-95):(5-35), and the total volume of the two is 100%, that is, the volume fraction of hard particles in the reinforcing phase is as high as 65%-95%;

[0005] (2) Matrix pretreatment: The aluminum alloy matrix surface is polished and cleaned, and then a matrix groove is prefabricated;

[0006] (3) Encapsulation treatment: The reinforcing phase slurry is evenly dropped into the matrix groove. After the solvent volatilizes completely, the reinforcing phase is encapsulated in the matrix groove with a needleless stirring head;

[0007] (4) Special stirring head friction stir processing: A special needle stirring head is used to perform friction stir processing on the reinforcing phase in the matrix groove to make the reinforcing phase composite with the aluminum alloy matrix;

[0008] The structure of the special pin-type stirring head is as follows: It is integrally formed by a stirring pin and a main body shaft. The stirring pin has a quadrangular prism structure with a narrow top and a wide bottom, and the bottom of the stirring pin intersects with the top of the main body shaft; the edges at the intersections of the side planes of the stirring pin are rounded to form curved surfaces, and grooves are provided on the top, side planes, and curved surfaces of the stirring pin; the main body shaft is cylindrical, and the plane on the top of the main body shaft that intersects with the bottom of the stirring pin is denoted as the shoulder, and the shoulder is provided with a groove;

[0009] (5) Heat treatment: After friction stir processing, solution treatment and aging treatment are carried out to obtain a high volume fraction particle-reinforced aluminum matrix surface composite material.

[0010] In step (1), the volume ratio of the hard particles to the lubricating particles in the reinforcement is (70 - 80):(20 - 30);

[0011] The hard particles include at least one of SiC, Al2O3, TiC, B4C, c-BN, and the size of the hard particles is 1μm - 50μm; the lubricating particles have a two-dimensional layered structure and include at least one of graphene, h-BN, MoS2, the thickness of the lubricating particles is 5μm - 100nm, and the size is 50nm - 50μm;

[0012] A volatile solvent is added to the reinforcement and ultrasonic treatment is carried out to obtain a reinforcement slurry; the volatile solvent includes ethanol, methanol, or acetone, and the ultrasonic treatment is carried out for 10min - 30min.

[0013] In step (2), the depth of the groove is 2mm - 8mm, and the width is 2mm - 8mm; the aluminum alloy matrix is a heat-treatable aluminum alloy, such as based on 2xxx series, 6xxx series, 7xxx series aluminum alloys.

[0014] In step (3), the encapsulation conditions are as follows: A non-pin stirring head with a diameter of 10mm - 20mm (made of 8433 hot work die steel) is used to encapsulate the reinforcement in the matrix groove, and the stirring parameters during encapsulation are: rotational speed: 1000rpm - 2000rpm, processing speed: 30mm / min - 60mm / min, stirring head inclination angle: 0° - 3°.

[0015] In step (4), the top of the stirring pin has a cross-shaped groove, and the side plane has several right-handed thread grooves; the shoulder of the main body shaft has several spiral grooves;

[0016] Preferably, the cross-shaped groove at the top of the stirring pin is connected to a certain thread groove on the side plane and a certain groove on the curved surface;

[0017] Preferably, the shoulder of the main body shaft is provided with six spiral grooves;

[0018] Preferably, the top and bottom of the stirring pin are square.

[0019] The specific parameters of the special pin-type stirring head are as follows: The material is 8433 hot work die steel. The bottom side length of the stirring pin is 3 mm to 6 mm, the top side length is 0.5 mm to 2 mm smaller than the bottom side length, the height is 4 mm to 6 mm, and the edge fillet radius is 0.3 mm to 0.6 mm; The depth of the right-handed thread groove on the side plane of the stirring pin is 0.2 mm to 0.5 mm, the pitch is 1.5 mm to 3 mm, the depth of the groove at the curved surface edge is 0.2 mm to 0.5 mm, and the width is 0.8 mm to 1.5 mm (this width is based on the width of the cross groove and the pitch); The depth of the cross groove at the top of the stirring pin is 0.3 mm to 0.6 mm, the width is 0.6 mm to 1.2 mm, the shoulder diameter of the main shaft is 10 mm to 20 mm, the depth of the groove at the shoulder is 0.3 mm to 1 mm, the width is 0.8 mm to 2.0 mm, and the helix angle is 10° to 15°.

[0020] The friction stir conditions are as follows: The special pin-type stirring head moving from the initial end of the matrix groove to the other end of the matrix groove by friction stir is recorded as one pass, and moving from the other end of the matrix groove back to the initial end by friction stir is recorded as two passes, and so on. The reinforced phase in the matrix groove is subjected to 3 to 6 passes of friction stir processing. During the friction stir process, the rotation speed of the special pin-type stirring head: 1000 rpm to 2000 rpm, the processing speed: 30 mm / min to 60 mm / min, and the inclination angle of the stirring head: 0° to 3°.

[0021] In step (5), the heat treatment includes the following contents:

[0022] When the 2xxx series aluminum alloy is selected as the matrix, the solution treatment temperature is 495 °C to 535 °C, hold for 1 h to 2 h, water quench, and then perform aging treatment. The aging treatment temperature is 165 °C to 195 °C, hold for 12 h to 24 h, and air cool;

[0023] When the 6xxx series aluminum alloy is selected as the matrix, the solution treatment temperature is 520 °C to 560 °C, hold for 1 h to 2 h, water quench, and then perform aging treatment. The aging treatment temperature is 165 °C to 185 °C, hold for 8 h to 12 h, and air cool;

[0024] When the 7xxx series aluminum alloy is selected as the matrix, the solution treatment temperature is 460 °C to 490 °C, hold for 1 h to 2 h, water quench, and then perform aging treatment. The aging treatment temperature is 120 °C to 150 °C, hold for 12 h to 24 h, and air cool.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention optimizes the distribution of hard particles. The introduced two-dimensional layered particles play an interface regulation role during the friction stir processing, effectively isolating the direct contact between hard particles, reducing the friction coefficient between particles, inhibiting the agglomeration phenomenon. The lamellar structure of the two-dimensional layered particles can promote the plastic flow of the matrix material, improve the dispersion effect of hard particles. At the same time, multi-pass reverse stirring processing eliminates the non-uniformity of plastic deformation on the advancing side and the retreating side of the stirring zone, and the increased plastic deformation further optimizes the particle distribution. The special stirring head in the present invention provides a flow channel for the incompressible material. The six-helix grooves on the shoulder provide a transverse flow path from the outside to the inside for the surface material. The groove design of the stirring pin improves the longitudinal fluidity of the material from the surface to the inside, and the cross grooves at the top improve the transverse fluidity of the internal material from the inside to the outside. The overall design of the shoulder and the stirring pin provides multiple continuous paths for material flow, increasing the overall material fluidity, and thus eliminating the phenomenon of particle segregation;

[0027] 2. The present invention improves the microstructure of the composite material. The addition of two-dimensional layered particles refines the matrix grains, provides additional nucleation sites. The uniformly distributed hard particles and two-dimensional layered particles jointly pin the grain boundaries, inhibit grain growth. The formed good interfacial bonding promotes the effective transfer of load, improves the comprehensive mechanical properties of the material. The fine nano-scale θ phase and θ' phase (2xxx series), β” and β' phase (6xxx series), η' phase (7xxx series) precipitated by solution aging improve the strength and hardness of the base material by pinning dislocations to prevent their slip;

[0028] 3. The present invention improves the wear resistance of the composite material. The two-dimensional layered particles inhibit particle agglomeration, and thus a high volume fraction particle-reinforced aluminum matrix composite material is realized. The hard particles provide stable load-bearing support. The two-dimensional layered particles form an effective self-lubricating protective film during the wear process. Both simultaneously pin dislocations, strengthening the anti-deformation ability of the material. The overall synergistic effect significantly improves the wear resistance of the composite material;

[0029] 4. The present invention reduces the wear loss of the stirring head. The two-dimensional layered particles reduce the friction coefficient between the stirring head and hard particles, avoiding their direct contact to a certain extent, thereby increasing the service life of the stirring head.

[0030] 5. The present invention applies the friction stir welding process to the surface modification of aluminum matrix, optimizes the structure of the stirring pin, and realizes the modification effect on the surface of high volume fraction particle-reinforced aluminum matrix. The preparation process of the high volume fraction particle-reinforced aluminum matrix surface composite material by the friction stir processing is simple, easy to operate, and suitable for popularization. Description of the Drawings

[0031] Figure 1Schematic diagram of the structure of the special pin-type stirring head for the present invention; wherein: 1 - Right-handed thread groove on the side plane of the stirring pin, 2 - Curved edge groove, 3 - Cross groove at the top of the stirring pin, 4 - Shoulder spiral groove;

[0032] Figure 2 Schematic diagram of the encapsulation of the non-pin stirring head for the present invention;

[0033] Figure 3 Schematic diagram of multi-pass reverse machining during the compounding of the special pin-type stirring head for the present invention;

[0034] Figure 4 Metallographic picture of the composite material obtained in Example 1 of the present invention;

[0035] Figure 5 Transmission picture of the composite material obtained in Example 1 of the present invention; wherein: 1 - h-BN particles, 2 - B4C particles;

[0036] Figure 6 Scanning electron microscope picture of the worn composite material obtained in Example 1 of the present invention. Specific embodiments

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments and the drawings. It should be noted that the embodiments described in the present invention are only used for further explanation and illustration, rather than limiting its application scope. Based on the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0038] The structure of the special pin-type stirring head of the present invention is as Figure 1 shown, the schematic diagram of the encapsulation with a non-pin stirring head is as Figure 2 shown, and the schematic diagram of multi-pass friction stir processing of the reinforcing phase in the matrix groove by the special pin-type stirring head is as Figure 3 shown. Taking the first pass from right to left as an example, the second pass is from left to right, and the third pass is from right to left again, and so on. The number of passes ≤ 6. The specific number of passes is based on the uniform distribution of the particles, and the processing efficiency is improved with fewer passes.

[0039] The width and depth of the matrix groove are given in the embodiments, and the length of the matrix groove can be determined according to actual needs, and the width and depth of the matrix groove can be adjusted. The materials of the non-pin stirring head for encapsulation and the special pin-type stirring head are both 8433 hot work die steel, and the sizes of the non-pin stirring head for encapsulation and the special pin-type stirring head, as well as the stirring parameters and steel grades, can be adjusted according to actual needs.

[0040] The wear resistance test method in the embodiment is as follows: The composite material is subjected to a dry friction sliding wear test with a YG6X tungsten carbide ball under the conditions of a load of 5 N and a sliding speed of 5 mm / s. The worn volume after wear is calculated by a three-dimensional profiler, and the wear rate is calculated to further obtain the improvement degree of wear resistance.

[0041] Example 1

[0042] Using 6061 aluminum alloy as the matrix, the volume fraction of hard particles in the reinforcing phase is 80%.

[0043] (1) Prepare a reinforcing phase with a high volume fraction: Select a mixed particle composed of B4C hard particles and h-BN lubricating particles as the reinforcing phase. The average particle size of the hard particles is 6 μm, the average size of the lubricating particles is 7 μm, and the thickness is about 30 nm. The volume ratio of the hard particles to the lubricating particles is 80:20; After mixing B4C and h-BN, add methanol and ultrasonically treat for 20 min to obtain a reinforcing phase slurry.

[0044] (2) Matrix pretreatment: Grind and clean the surface of the 6061 aluminum alloy, and then prefabricate a matrix groove. The depth of the matrix groove is 4 mm and the width is 4 mm.

[0045] (3) Encapsulation treatment: Drop the reinforcing phase slurry into the matrix groove and let it dry naturally. After the solvent has completely evaporated, encapsulate the reinforcing phase in the matrix groove with a needleless stirring head; The diameter of the needleless stirring head is 18 mm. During the encapsulation process, the rotation speed of the needleless stirring head is 1500 rpm, the processing speed is 40 mm / min, and the inclination angle is 3°.

[0046] (4) Special stirring head friction stir processing: Use a special needle stirring head to perform 4 passes of friction stir processing on the reinforcing phase in the matrix groove. During the friction stir process, the rotation speed of the special needle stirring head is 1500 rpm, the processing speed is 40 mm / min, and the inclination angle of the stirring head is 3°.

[0047] The structure of the special needle stirring head is as follows: It is integrally formed by a stirring needle and a main shaft. The main shaft is coaxial with the central axis of the stirring needle. The stirring needle is a quadrangular prism structure with a narrow top and a wide bottom. Both the top and bottom of the stirring needle are squares, and the bottom of the stirring needle intersects with the top plane of the main shaft; The edge at the intersection of the side planes of the stirring needle is rounded and recorded as a curved surface edge; The top of the stirring needle is provided with a cross-shaped groove, the side plane is provided with a right-handed thread groove, and the curved surface edge is provided with a groove; The main shaft is cylindrical. The plane on the top of the main shaft that intersects with the bottom of the stirring needle is recorded as a shoulder. The shoulder is provided with six spiral grooves.

[0048] The specific parameters of the special pin-type stirring head are as follows: the diameter of the stirring head shoulder is 18 mm, the bottom side length of the stirring pin is 5 mm, the top side length is 4 mm, the height is 4 mm, the edge rounding radius is 0.5 mm, the depth of the right-handed thread groove on the side plane of the stirring pin is 0.3 mm, the pitch is 1.5 mm, the depth of the groove at the curved edge is 0.3 mm, the depth of the cross groove at the top of the stirring pin is 0.3 mm, the width is 0.6 mm, the depth of the six-helix groove at the shoulder is 1 mm, the width is 1 mm, and the helix angle is 10°;

[0049] (5) Heat treatment: Solution treatment and aging treatment are carried out after friction stir processing; the solution treatment is to hold at 550 °C for 1.5 h, water quench, and then carry out aging treatment. The aging treatment is to hold at 180 °C for 10 h and air cool; a high volume fraction of particle-reinforced aluminum matrix surface composite material is obtained.

[0050] As Figure 4 shown, the metallographic photograph of the high volume fraction of particle-reinforced aluminum matrix composite material prepared in this embodiment shows that the hard particles are evenly distributed in the matrix, and there are almost no defects such as agglomeration and pores. Figure 5 is the transmission electron microscope photograph of the composite material, showing that the h-BN lubricating particles (marked as 1) are evenly distributed between the B4C hard particles (marked as 2) and form a good interfacial bond with the matrix. Figure 6 is the worn surface morphology of the material after the dry friction sliding wear test using a YG6X tungsten carbide ball under the conditions of a load of 5 N and a sliding speed of 5 mm / s. The results show that due to the lubricating effect of h-BN, the wear mechanism of the composite material changes from severe adhesive wear to mild abrasive wear, and the wear resistance of the composite material is improved by more than 95% compared with the matrix material.

[0051] Example 2

[0052] Using 2024 aluminum alloy as the matrix, the volume fraction of hard particles in the reinforcement phase is 85%.

[0053] (1) Prepare a reinforcement phase with a high volume fraction: Select a mixed particle composed of SiC hard particles and graphene lubricating particles as the reinforcement phase. The average particle size of the hard particles is 10 μm, the average size of the lubricating particles is 500 nm, and the volume ratio of the hard particles to the lubricating particles is 85:15; after mixing SiC and graphene, add ethanol and ultrasonically treat for 15 min to obtain the reinforcement phase slurry;

[0054] (2) Matrix pretreatment: Grind and clean the surface of the 2024 aluminum alloy and then prefabricate matrix grooves. The depth of the matrix grooves is 3 mm and the width is 4 mm;

[0055] (3) Encapsulation treatment: Drop the reinforcing phase slurry into the matrix groove, let it dry naturally, and after the solvent has completely evaporated, encapsulate the reinforcing phase in the matrix groove with a needleless stirring head; the diameter of the needleless stirring head is 15 mm, the rotation speed of the needleless stirring head during encapsulation is 1200 rpm, the processing speed is 35 mm / min, and the inclination angle is 2°;

[0056] (4) Friction stir processing with a special stirring head: Use a special needle stirring head to perform 6 passes of friction stir processing on the reinforcing phase in the matrix groove. During the friction stir process, the rotation speed of the special needle stirring head is 1200 rpm, the processing speed is 35 mm / min, and the inclination angle is 2°;

[0057] The structure of the special needle stirring head is the same as that in Example 1;

[0058] The specific parameters of the special needle stirring head are as follows: the diameter of the stirring head shoulder is 15 mm, the bottom side length of the stirring pin is 5 mm, the top side length is 4 mm, the height is 3 mm, the edge rounding radius is 0.5 mm, the depth of the right-handed thread groove on the side plane of the stirring pin is 0.4 mm, the pitch is 1.5 mm, the depth of the groove at the curved edge is 0.4 mm, the depth of the cross groove at the top of the stirring pin is 0.4 mm, the width is 0.6 mm, the depth of the six-helix groove at the shoulder is 1 mm, the width is 1.2 mm, and the helix angle is 12°;

[0059] (5) Heat treatment: Perform solution treatment and aging treatment after friction stir processing; the solution treatment is to hold at 515 °C for 1.5 h, water quench, and then perform aging treatment. The aging treatment is to hold at 180 °C for 18 h and air cool; obtain a high volume fraction particle-reinforced aluminum matrix surface composite material.

[0060] The microstructure of the prepared composite material shows that the added graphene effectively prevents the agglomeration of SiC particles. The wear resistance test results show that the wear resistance of the composite material is increased by 90% compared with the matrix material.

[0061] Example 3

[0062] Using 7075 aluminum alloy as the matrix, the volume fraction of hard particles in the reinforcing phase is 90%.

[0063] (1) Prepare a reinforcing phase with a high volume fraction: Select a mixed particle composed of TiC hard particles and MoS2 lubricating particles as the reinforcing phase. The average particle size of the hard particles is 8 μm, the average size of the lubricating particles is 1 μm, and the volume ratio of the hard particles to the lubricating particles is 90:10; After mixing TiC and MoS2, add acetone and perform ultrasonic treatment for 25 min to obtain a reinforcing phase slurry;

[0064] (2) Matrix pretreatment: Polish and clean the surface of the 7075 aluminum alloy, and then prefabricate a matrix groove. The depth of the matrix groove is 5 mm and the width is 5 mm;

[0065] (3) Encapsulation treatment: Drop the reinforced phase slurry into the groove, let it dry naturally, and after the solvent has completely evaporated, encapsulate the reinforced phase in the matrix groove with a needleless stirring head; the diameter of the needleless stirring head is 16 mm, the rotation speed of the needleless stirring head during encapsulation is 1800 rpm, the processing speed is 45 mm / min, and the inclination angle is 2.5°;

[0066] (4) Friction stir processing with a special stirring head: Use a special needle-type stirring head to perform 5 passes of friction stir processing on the reinforced phase in the matrix groove. During the friction stir process, the rotation speed of the special needle-type stirring head is 1800 rpm, the processing speed is 45 mm / min, and the inclination angle is 2.5°;

[0067] The structure of the special needle-type stirring head is the same as that in Example 1;

[0068] The specific parameters of the special needle-type stirring head are as follows: the diameter of the stirring head shoulder is 16 mm, the bottom side length of the stirring pin is 5 mm, the top side length is 4 mm, the height is 5 mm, the fillet radius of the edge is 0.5 mm, the depth of the right-handed thread groove on the side plane of the stirring pin is 0.4 mm, the pitch is 2 mm, the depth of the groove at the curved surface edge is 0.4 mm, the depth of the cross groove at the top of the stirring pin is 0.4 mm, the width is 1 mm, the depth of the six-helix groove at the shoulder is 1 mm, the width is 1.5 mm, and the helix angle is 15°;

[0069] (5) Heat treatment: After friction stir processing, solution treatment and aging treatment are carried out; the solution treatment is to hold at 470 °C for 1.5 h, water quench, and then carry out aging treatment. The aging treatment is to hold at 135 °C for 18 h and air cool; a high volume fraction particle-reinforced aluminum matrix surface composite material is obtained.

[0070] The prepared composite material has a dense structure, uniform distribution of TiC particles, and MoS2 plays a good lubricating role during the wear process. The wear resistance of the composite material is improved by more than 82% compared with the matrix material.

[0071] Example 4

[0072] Using 6061 aluminum alloy as the matrix, the volume fraction of hard particles in the reinforced phase is 75%.

[0073] (1) Prepare a reinforced phase with a high volume fraction: Select a mixed particle composed of Al2O3 hard particles and h-BN lubricating particles as the reinforced phase. The average particle size of the hard particles is 12 μm, the average size of the lubricating particles is 10 μm, and the volume ratio of the hard particles to the lubricating particles is 75:25; After mixing Al2O3 and h-BN, add methanol and perform ultrasonic treatment for 30 min to obtain the reinforced phase slurry;

[0074] (2) Matrix pretreatment: Grind and clean the surface of 6061 aluminum alloy, and then prefabricate a matrix groove. The depth of the matrix groove is 6 mm and the width is 6 mm;

[0075] (3) Encapsulation treatment: Drop the reinforcing phase slurry into the groove, let it dry naturally, and after the solvent has completely evaporated, encapsulate the reinforcing phase in the matrix groove with a needleless stirring head; the diameter of the needleless stirring head is 20 mm, during the encapsulation process, the rotational speed of the needleless stirring head is 1600 rpm, the processing speed is 50 mm / min, and the inclination angle is 2°;

[0076] (4) Friction stir processing with a special stirring head: Use a special needle stirring head to perform 6 passes of friction stir processing on the reinforcing phase in the matrix groove. During the friction stir process, the rotational speed of the special needle stirring head is 1600 rpm, the processing speed is 50 mm / min, and the inclination angle is 2°;

[0077] The structure of the special needle stirring head is the same as that in Example 1;

[0078] The specific parameters of the special needle stirring head are as follows: the diameter of the stirring head shoulder is 20 mm, the bottom side length of the stirring needle is 6 mm, the top side length is 5 mm, the height is 6 mm, the edge fillet radius is 0.6 mm, the depth of the right-handed thread groove on the side plane of the stirring needle is 0.3 mm, the pitch is 1.5 mm, the depth of the groove at the curved surface edge is 0.3 mm, the depth of the cross groove at the top of the stirring needle is 0.3 mm, the width is 0.8 mm, the depth of the six-helix groove at the shoulder is 1 mm, the width is 1.2 mm, and the helix angle is 12°;

[0079] (5) Heat treatment: After friction stir processing, solution treatment and aging treatment are carried out; the solution treatment is to hold at 540 °C for 1 h, water quench, and then carry out aging treatment. The aging treatment is to hold at 170 °C for 10 h and air cool; a high volume fraction particle-reinforced aluminum matrix surface composite material is obtained.

[0080] Both the hardness and wear resistance of the composite material are better than those of the sample that only adds hard particles without adding h-BN. The hardness is increased by more than 30 HV, and the wear resistance is increased by more than 45%, indicating that the addition of two-dimensional layered particles significantly improves the material properties.

[0081] Example 5

[0082] Using 7075 aluminum alloy as the matrix, the volume fraction of hard particles in the reinforcing phase is 95%.

[0083] (1) Prepare a reinforcing phase with a high volume fraction: Select a mixed particle composed of c-BN hard particles and graphene lubricating particles as the reinforcing phase. The average particle size of the hard particles is 15 μm, the average size of the lubricating particles is 50 nm, and the volume ratio of the hard particles to the lubricating particles is 95:5; after mixing c-BN and graphene, add acetone and perform ultrasonic treatment for 20 min to obtain the reinforcing phase slurry;

[0084] (2) Matrix pretreatment: Grind and clean the surface of the 7075 aluminum alloy and then prefabricate a matrix groove. The depth of the matrix groove is 4.5 mm and the width is 4.5 mm;

[0085] (3) Encapsulation treatment: Drop the reinforced phase slurry into the groove, let it dry naturally. After the solvent has completely volatilized, encapsulate the reinforced phase in the matrix groove with a needleless stirring head; the diameter of the needleless stirring head is 17 mm. During the encapsulation process, the rotation speed of the needleless stirring head is 1700 rpm, the processing speed is 55 mm / min, and the inclination angle is 1.5°;

[0086] (4) Friction stir processing with a special stirring head: Use a special needle stirring head to perform 4 passes of friction stir processing on the reinforced phase in the matrix groove. During the friction stir process, the rotation speed of the special needle stirring head is 1700 rpm, the processing speed is 55 mm / min, and the inclination angle is 1.5°;

[0087] The structure of the special needle stirring head is the same as that in Example 1;

[0088] The specific parameters of the special needle stirring head are as follows: the diameter of the shoulder of the stirring head is 17 mm, the bottom side length of the stirring needle is 4.5 mm, the height is 4.5 mm, the radius of the chamfered edge is 0.4 mm, the depth of the right-handed thread groove on the side plane of the stirring needle is 0.4 mm, the pitch is 1.5 mm, the depth of the groove at the curved surface edge is 0.4 mm, the depth of the cross groove at the top of the stirring needle is 0.4 mm, the width is 1 mm, the depth of the six-helix groove at the shoulder is 1 mm, the width is 1 mm, and the helix angle is 10°;

[0089] (5) Heat treatment: After friction stir processing, solution treatment and aging treatment are carried out. The solution treatment is to hold at 480 °C for 2 h, followed by water quenching, and then aging treatment. The aging treatment is to hold at 130 °C for 24 h and then air-cooled; a high volume fraction particle-reinforced aluminum matrix surface composite material is obtained.

[0090] The composite material exhibits excellent comprehensive properties. The hard particles are evenly distributed and well combined with the matrix. The wear resistance of the composite material is improved by more than 78% compared with the matrix material.

[0091] Example 6

[0092] Using 2024 aluminum alloy as the matrix, the volume fraction of hard particles in the reinforced phase is 70%.

[0093] (1) Prepare a reinforced phase with a high volume fraction: Select a mixed particle composed of TiC hard particles and MoS2 lubricating particles as the reinforced phase. The average particle size of the hard particles is 5 μm, the average size of the lubricating particles is 400 nm, and the volume ratio of the hard particles to the lubricating particles is 70:30; After mixing TiC and MoS2, add ethanol and perform ultrasonic treatment for 25 min to obtain a reinforced phase slurry;

[0094] (2) Matrix pretreatment: Grind and clean the surface of 2024 aluminum alloy, and then prefabricate a matrix groove. The depth of the matrix groove is 5.5 mm and the width is 5.5 mm;

[0095] (3) Encapsulation treatment: Drop the reinforced phase slurry into the groove, let it dry naturally, and after the solvent has completely evaporated, encapsulate the reinforced phase in the matrix groove with a needleless stirring head; the diameter of the needleless stirring head is 19 mm, during the encapsulation process, the rotation speed of the needleless stirring head is 1900 rpm, the processing speed is 45 mm / min, and the inclination angle is 2°;

[0096] (4) Friction stir processing with a special stirring head: Use a special needle stirring head to perform 5 passes of friction stir processing on the reinforced phase in the matrix groove. During the friction stir process, the rotation speed of the special needle stirring head is 1900 rpm, the processing speed is 45 mm / min, and the inclination angle is 2°;

[0097] The structure of the special needle stirring head is the same as that in Example 1;

[0098] The specific parameters of the special needle stirring head are as follows: the diameter of the shoulder of the stirring head is 19 mm, the bottom side length of the stirring needle is 5.5 mm, the top side length is 4 mm, the height is 5.5 mm, the edge fillet radius is 0.4 mm, the depth of the right-handed thread groove on the side plane of the stirring needle is 0.4 mm, the pitch is 3 mm, the depth of the groove at the curved surface edge is 0.4 mm, the depth of the cross groove at the top of the stirring needle is 0.6 mm, the width is 1.2 mm, the depth of the six-helix groove at the shoulder is 0.8 mm, the width is 1.2 mm, and the helix angle is 12°;

[0099] (5) Heat treatment: Perform solution treatment and aging treatment after friction stir processing; the solution treatment is to hold at 505 °C for 1.5 h, water quench, and then perform aging treatment. The aging treatment is to hold at 185 °C for 16 h and air cool; obtain a high volume fraction of particle-reinforced aluminum matrix surface composite material.

[0100] In the prepared composite material, the TiC particles are evenly distributed, and MoS2 forms a good interfacial transition layer between the particles. The composite material exhibits excellent wear resistance and mechanical properties. The wear resistance is increased by more than 90% compared with the matrix material, and the tensile strength is increased by 80 Mpa compared with the matrix material (measured with a non-standard sample, under the same test conditions, ensuring that the tensile cross-section is 2 mm × 2 mm).

[0101] Comparative Example 1

[0102] The influence of different stirring head shapes on the distribution of the reinforced phase.

[0103] Using 6061 aluminum alloy as the matrix, the volume fraction of hard particles in the reinforced phase is 80%.

[0104] (1) Prepare a reinforced phase with a high volume fraction: Select a mixed particle composed of SiC hard particles and h-BN lubricating particles as the reinforced phase. The average particle size of the hard particles is 8 μm, the average size of the lubricating particles is 5 μm, and the thickness is about 25 nm. The volume ratio of the hard particles to the lubricating particles is 80:20; the slurry preparation method is the same as that in Example 1;

[0105] (2) Substrate pretreatment: Select 4 6061 aluminum alloy substrates of the same specification. The method for preparing the substrate grooves is the same as that in Example 1;

[0106] (3) Encapsulation treatment: Drop the reinforcing phase slurry into the 4 substrate grooves respectively. The encapsulation method is the same as that in Example 1;

[0107] (4) Stirring head friction stir treatment: Use the special designed needle-shaped stirring head, cylindrical stirring head, conical stirring head and square stirring head of the present invention to carry out friction stir processing on the reinforcing phase encapsulated in each substrate groove respectively. Except for the shape of the stirring head, other process parameters during the friction stir process remain the same: rotation speed 1500 rpm, processing speed 40 mm / min, inclination angle 3°, and 4 processing passes.

[0108] The structure and parameters of the special designed needle-shaped stirring head are the same as those in Example 1;

[0109] The specific parameters of the cylindrical stirring head are as follows: the diameter of the stirring head shoulder is 18 mm, the diameter of the stirring pin is 4.5 mm, and the height is 4 mm;

[0110] The specific parameters of the conical stirring head are as follows: the diameter of the stirring head shoulder is 18 mm, the bottom diameter of the stirring pin is 7 mm, the top diameter is 5.7 mm, and the height is 4 mm;

[0111] The specific parameters of the square stirring head are as follows: the diameter of the stirring head shoulder is 18 mm, the side length of the stirring pin is 4.5 mm, and the height is 4 mm;

[0112] (5) Heat treatment: The same as that in Example 1;

[0113] Arbitrarily select 9 micro-regions within the friction stir processing area of the substrate groove to evaluate the overall distribution of the reinforcing phase particles in the stirring area. The micro-region conditions of the composites obtained by processing with different stirring heads are as follows:

[0114] In the composite material prepared by the special designed needle-shaped stirring head of the present invention, the SiC hard particles and h-BN lubricating particles are evenly distributed, and there is almost no obvious agglomeration phenomenon; while in the composite material prepared by the square stirring head, the SiC particles are severely agglomerated, forming clusters with a size of 50 - 200 μm, and there are many hole defects in the stirring area; in the composite materials prepared by the conical and cylindrical stirring heads, the particle distribution situation is improved compared with the square stirring head, but there are still local agglomeration phenomena and uneven distribution.

[0115] In summary, the ranking of the uniformity of the reinforcing phase particles is as follows: the special designed needle-shaped stirring head of the present invention > cylindrical stirring head > conical stirring head > square stirring head. In the wear resistance test, the wear rate of the composite material prepared by the special designed needle-shaped stirring head of the present invention is reduced by 92% compared with the matrix, while the wear rates of the composite materials prepared by the cylindrical, conical and square stirring heads are reduced by 82%, 75% and 61% respectively compared with the matrix material.

[0116] The special designed needle-shaped stirring head of the present invention has multiple structural features (right-handed threaded grooves on the side plane of the stirring needle, curved edge grooves, cross grooves on the top of the stirring needle, six-helix grooves on the shoulder), which can significantly improve the material flow performance, promote the uniform distribution of the reinforcing phase, reduce the formation of defects, and has obvious process advantages compared with the traditional stirring head.

[0117] Comparative Example 2

[0118] The influence of different ratios of hard particles to lubricating particles on the properties of the composite material.

[0119] Using 7075 aluminum alloy as the matrix, the volume fractions of hard particles in each reinforcing phase are 50%, 60%, 70%, 80%, 90%, 95% respectively.

[0120] (1) Prepare the reinforcing phase with a high volume fraction: Select a mixed particle composed of B4C hard particles and graphene lubricating particles as the reinforcing phase. The average particle size of the hard particles is 10 μm, and the average size of the lubricating particles is 300 nm. Set different volume ratios of hard particles to lubricating particles: 95:5, 90:10, 80:20, 70:30, 60:40, 50:50; that is, the volume fractions of lubricating particles in each reinforcing phase are 5%, 10%, 20%, 30%, 40%, 50% respectively; Prepare the slurries according to the above ratios respectively, and the slurry preparation method is the same as that in Example 1;

[0121] (2) Matrix pretreatment: Select 6 pieces of 7075 aluminum alloy matrices with the same specifications, and the matrix groove preparation method is the same as that in Example 1;

[0122] (3) Encapsulation treatment: Drop the reinforcing phase slurries with different volume ratios into 6 matrix grooves respectively, and the encapsulation method is the same as that in Example 1;

[0123] (4) Stirring and friction treatment with the stirring head: Use the special designed needle-shaped stirring head of the present invention to perform stirring and friction processing on the reinforcing phase in each matrix groove respectively. During the stirring and friction process, the rotation speed of the special designed needle-shaped stirring head is 1600 rpm, the processing speed is 45 mm / min, the inclination angle is 3°, and the processing is carried out for 5 passes;

[0124] The structure of the special designed needle-shaped stirring head is the same as that in Example 1;

[0125] The specific parameters of the special pin stirrer head are as follows: the diameter of the stirrer head shoulder is 19 mm, the bottom side length of the stirring pin is 5.5 mm, the top side length is 4 mm, the height is 5.5 mm, the edge fillet radius is 0.4 mm, the depth of the right-handed thread groove on the side plane of the stirring pin is 0.4 mm, the pitch is 3 mm, the depth of the groove at the curved surface edge is 0.4 mm, the depth of the cross groove at the top of the stirring pin is 0.6 mm, the width is 1.2 mm, the depth of the six-helix groove at the shoulder is 0.8 mm, the width is 1.2 mm, and the helix angle is 12°;

[0126] (5) Heat treatment: Solution and aging treatments are carried out after friction stir processing. The solution treatment is to hold at 480 °C for 1.5 h, followed by water quenching, and then aging treatment. The aging treatment is to hold at 135 °C for 20 h and air-cool. Five high-volume fraction particle-reinforced aluminum matrix surface composite materials with different volume ratios of the reinforcement phase are obtained.

[0127] For the composite materials prepared by using the special pin stirrer head of the present invention when the reinforcement phase has different volume ratios, the distribution of particles in the reinforcement phase is generally relatively uniform. For different volume ratios, specifically, as the proportion of lubricating particles in the reinforcement phase increases, the agglomeration phenomenon of hard particles significantly decreases and the distribution becomes more uniform. When the volume ratio of lubricating particles in the reinforcement phase is 5%, agglomeration of B4C particles is observed, and the size of the agglomeration region is about 30 μm - 100 μm. When the volume ratio of lubricating particles in the reinforcement phase is 20% - 30%, the distribution of B4C particles is the most uniform, with almost no agglomeration phenomenon, and the denseness of the composite layer is the highest. When the volume ratio of lubricating particles in the reinforcement phase further increases to 40% - 50%, although the distribution of B4C particles is still uniform, there are too many lubricating particles in the composite layer, resulting in a decrease in the overall strength and hardness.

[0128] Wear resistance test: When the volume ratio of lubricating particles in the reinforcement phase is 5% - 10%, obvious ploughing grooves and spalling areas appear on the worn surface, mainly adhesive wear and abrasive wear; when the volume ratio of lubricating particles in the reinforcement phase is 20% - 30%, the worn surface is smooth, a continuous lubricating film is formed, mainly showing slight abrasive wear; when the volume ratio of lubricating particles in the reinforcement phase is 40% - 50%, although the lubrication effect is good, due to the low proportion of hard particles, the anti-deformation ability of the composite layer decreases, and slight plastic deformation appears.

[0129] In summary, the optimal volume ratio of hard particles to lubricating particles is (70 - 80):(20 - 30). Within this ratio range, the composite material has excellent comprehensive properties: the hard particles are evenly distributed with almost no agglomeration; the defect rate of the composite layer is the lowest; the material has high hardness and strength while maintaining good toughness; the wear resistance is optimal, and the wear rate is reduced by 92% - 94% compared to the matrix material. When the proportion of lubricating particles is too low (<20%), the hard particles are prone to agglomeration, the defects in the composite layer increase, and the wear resistance decreases; when the proportion of lubricating particles is too high (>30%), although the lubrication effect is good, the overall mechanical properties of the material decrease.

[0130] Comparative Example 3

[0131] The influence of heat treatment on the properties of different series of aluminum alloy matrix composites.

[0132] 2024, 6061, and 7075 aluminum alloys were respectively selected as the matrix, and the volume fraction of hard particles in the reinforcement phase was 80%.

[0133] (1) Prepare a reinforcement phase with a high volume fraction: The reinforcement phase is a mixed particle composed of SiC hard particles and h - BN lubricating particles. The average particle size of the hard particles is 8μm, the average size of the lubricating particles is 6μm, and the thickness is about 30nm. The volume ratio of hard particles to lubricating particles is 80:20; the slurry preparation method is the same as that in Example 1;

[0134] (2) Matrix pretreatment: 2024, 6061, and 7075 aluminum alloys were respectively selected as the matrix, and 2 pieces of each series of matrix were selected. The matrix groove preparation method is the same as that in Example 1;

[0135] (3) Encapsulation treatment: The reinforcement phase slurry was respectively dropped into 6 matrix grooves, and the encapsulation method is the same as that in Example 1;

[0136] (4) Special stirring head friction stir processing: Use the special needle - equipped stirring head designed in the present invention to perform friction stir processing on the reinforcement phase in each matrix groove respectively. During the friction stir process, the rotation speed of the special needle - equipped stirring head is 1500rpm, the processing speed is 40mm / min, the inclination angle is 3°, and the processing is carried out for 4 passes.

[0137] The structure of the special needle - equipped stirring head is the same as that in Example 1, and the parameters are the same as those in Comparative Example 2;

[0138] (5) Heat treatment: The matrix materials of different series were divided into a heat treatment group and a non - heat treatment group. The non - heat treatment group obtained non - heat - treated composite materials after step (4), and the heat treatment group obtained heat - treated composite materials after heat treatment;

[0139] 2024 Matrix: In the non-heat-treated state, the SiC and h-BN particles are evenly distributed in the microstructure of the 2024 non-heat-treated composite material, but the matrix microstructure is relatively coarse, with a grain size of about 24 μm to 31 μm. After the 2024 heat-treated composite material is subjected to solution treatment (quenched in water after holding at 515 °C for 1.5 h) and aging treatment (air-cooled after holding at 180 °C for 18 h), the matrix grains are significantly refined, with an average size of about 15 μm to 25 μm. At the same time, a large number of nano-scale θ' phases (Al2Cu) are observed to be evenly distributed in the matrix. The combined action of these precipitates and the dispersed SiC and h-BN particles significantly improves the hardness and strength of the material.

[0140] 6061 Matrix: In the non-heat-treated state, the particles in the 6061 non-heat-treated composite material are evenly distributed, and the matrix grain size is about 18 - 24 μm. After the 6061 heat-treated composite material is subjected to solution treatment (quenched in water after holding at 540 °C for 1.5 h) and aging treatment (air-cooled after holding at 170 °C for 10 h), the matrix grains are refined to 12 μm to 20 μm, and a large number of nano-scale β” phases (Mg2Si) precipitates are formed. These precipitates effectively pin the dislocations, improving the strength of the material. At the same time, the combined action with the dispersed hard particles and lubricating particles significantly improves the wear resistance of the material.

[0141] 7075 Matrix: In the non-heat-treated state, the particles in the 7075 non-heat-treated composite material are evenly distributed, and the matrix grain size is about 16 μm to 28 μm. After the 7075 heat-treated composite material is subjected to solution treatment (quenched in water after holding at 480 °C for 1.5 h) and aging treatment (air-cooled after holding at 135 °C for 20 h), the matrix grains are refined to 10 μm to 18 μm, and a high density of η' phase (MgZn2) nano-precipitates are formed. These precipitates are evenly distributed in the matrix and, together with the dispersed SiC and h-BN particles, significantly improve the hardness and strength of the material, and the wear resistance is the most excellent.

[0142] Through the wear resistance test, the results show that the wear resistance of the heat-treated composite material is significantly improved: the wear rate of the 2024 heat-treated composite material is reduced by 18% compared with that of the 2024 non-heat-treated composite material; the wear rate of the 6061 heat-treated composite material is reduced by 20% compared with that of the 6061 non-heat-treated composite material; the wear rate of the 7075 heat-treated composite material is reduced by 17% compared with that of the 7075 non-heat-treated composite material.

[0143] Appropriate heat treatment processes have a significant improvement effect on the properties of different series of aluminum alloy matrix composites. Among them, the 7075 aluminum alloy matrix composite shows the most obvious performance improvement after heat treatment. Compared with the non-heat-treated 7075 composite, the hardness increases by about 50 HV, the tensile strength increases by about 100 MPa, and the wear resistance improves by 17%. This is mainly attributed to the synergistic effect of the high-density η' phase (MgZn2) nano-precipitates formed during the heat treatment process and the dispersed reinforcement phase particles, which significantly improve the mechanical properties and wear resistance of the material. The 2024 and 6061 aluminum alloy matrix composites also show a similar performance improvement trend after heat treatment compared with the non-heat-treated composites, but the degree is slightly lower than that of the 7075 aluminum alloy matrix composite.

Claims

1. A method for friction stir processing the surface of an aluminum matrix reinforced with high volume fraction particles, characterized in that, It includes the following steps: (1) Prepare an enhanced phase with a high volume fraction: A mixed particle composed of hard particles and lubricating particles is used as the enhanced phase. In the enhanced phase, the hard particles and the lubricating particles are mixed at a volume ratio of (65 - 95):(5 - 35), and the total volume of the two is 100%; (2) Matrix pretreatment: Pre - fabricate matrix grooves on the surface of the aluminum alloy matrix; (3) Encapsulation treatment: Encapsulate the enhanced phase in the matrix grooves; (4) Friction stir processing with a special pin - type stirrer: Use a special pin - type stirrer to perform friction stir processing on the enhanced phase in the matrix grooves to make the enhanced phase composite with the aluminum alloy matrix; The structure of the special pin - type stirrer is as follows: It is integrally formed by a stirring pin and a main body shaft. The stirring pin is a quadrangular prism structure with a narrow top and a wide bottom, and the bottom of the stirring pin intersects with the top of the main body shaft; The edge at the intersection of the side planes of the stirring pin is rounded to form a curved surface edge, and grooves are provided on the top, side planes, and curved surface edges of the stirring pin; The main body shaft is cylindrical, and the plane on the top of the main body shaft that intersects with the bottom of the stirring pin is denoted as the shoulder, and grooves are provided on the shoulder; (5) Heat treatment: After friction stir processing, solution treatment and aging treatment are carried out to obtain a high - volume - fraction particle - reinforced aluminum - based surface composite material.

2. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 1, wherein In the enhanced phase described in step (1), the volume ratio of the hard particles to the lubricating particles is (70 - 80):(20 - 30).

3. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 1, wherein The hard particles described in step (1) include at least one of SiC, Al2O3, TiC, B4C, c - BN, and the size of the hard particles is 1μm - 50μm; The lubricating particles have a two - dimensional layered structure and include at least one of graphene, h - BN, MoS2. The thickness of the lubricating particles is 5μm - 100nm, and the size is 50nm - 50μm.

4. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 1, characterized in that, The depth of the matrix grooves described in step (2) is 2mm - 8mm, and the width is 2mm - 8mm; The aluminum alloy matrix is a heat - treatable aluminum alloy, including 2xxx series, 6xxx series, and 7xxx series aluminum alloys.

5. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 1, wherein In step (1), a volatile solvent is added to the enhanced phase for ultrasonic treatment to obtain an enhanced - phase slurry, and then the enhanced - phase slurry is added to the matrix grooves; The volatile solvent includes ethanol, methanol, or acetone, and the ultrasonic treatment is carried out for 10min - 30min; The encapsulation treatment described in step (3) includes the following content: Add the enhanced - phase slurry to the matrix grooves. After the solvent has completely volatilized, use a non - pin stirrer to encapsulate the enhanced - phase slurry in the matrix grooves. The stirring parameters during the encapsulation process are: rotational speed: 1000rpm - 2000rpm, processing speed: 30mm / min - 60mm / min, stirrer inclination angle: 0° - 3°.

6. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 1, characterized in that, The top of the stirring pin described in step (4) has a cross - shaped groove, and the side planes have several right - hand threaded grooves; The shoulder of the main body shaft has several spiral grooves.

7. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 6, wherein The cross - shaped groove at the top of the stirring pin is connected to a certain threaded groove on the side plane and a certain groove on the curved surface edge; The top and bottom of the stirring pin are square; The shoulder of the main body shaft is provided with six spiral grooves.

8. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 6, wherein The specific parameters of the special pin stirring head described in step (4) are as follows: the bottom side length of the stirring pin is 3 mm to 6 mm, the top side length is 0.5 mm to 2 mm smaller than the bottom side length, and the height is 4 mm to 6 mm; the rounding radius of the edge is 0.3 mm to 0.6 mm; the depth of the right-handed thread groove on the side plane of the stirring pin is 0.2 mm to 0.5 mm, and the pitch is 1.5 mm to 3 mm; the depth of the groove at the curved surface edge is 0.2 mm to 0.5 mm, and the width is 0.8 mm to 1.5 mm; the depth of the cross groove at the top of the stirring pin is 0.3 mm to 0.6 mm, and the width is 0.6 mm to 1.2 mm; the diameter of the shoulder of the main body shaft is 10 mm to 20 mm, the depth of the groove at the shoulder is 0.3 mm to 1 mm, the width is 0.8 mm to 2.0 mm, and the helix angle is 10° to 15°.

9. The method for treating the surface of a high volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 1, characterized in that, The friction stir conditions described in step (4) are as follows: The special pin stirring head moving from the initial end of the matrix groove to the other end by friction stir is recorded as one pass, and moving from the other end of the matrix groove back to the initial end by friction stir is recorded as two passes, and so on. The reinforcing phase in the matrix groove is subjected to 3 to 6 passes of friction stir processing. During the friction stir process, the rotation speed of the special pin stirring head is 1000 rpm to 2000 rpm, the processing speed is 30 mm / min to 60 mm / min, and the inclination angle of the stirring head is 0° to 3°.

10. The method for treating the surface of a high-volume fraction particle-reinforced aluminum matrix by friction stir processing according to claim 1, wherein, The heat treatment described in step (5) includes the following: When using 2xxx series aluminum alloy as the matrix, the solution treatment temperature is 495°C to 535°C, holding for 1 h to 2 h, water quenching, and then aging treatment. The aging treatment temperature is 165°C to 195°C, holding for 12 h to 24 h, air cooling; When using 6xxx series aluminum alloy as the matrix, the solution treatment temperature is 520°C to 560°C, holding for 1 h to 2 h, water quenching, and then aging treatment. The aging treatment temperature is 165°C to 185°C, holding for 8 h to 12 h, air cooling; When using 7xxx series aluminum alloy as the matrix, the solution treatment temperature is 460°C to 490°C, holding for 1 h to 2 h, water quenching, and then aging treatment. The aging treatment temperature is 120°C to 150°C, holding for 12 h to 24 h, air cooling.

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