A friction stir welding method of high volume fraction ceramic particle reinforced aluminum matrix composites

Abstract

The application discloses a high-volume-fraction ceramic particle reinforced aluminum matrix composite material friction stir welding method and belongs to the technical field of welding. The method designs an H13 steel stirring pin for strengthening the material flow at the edge of the stirring pin, selects an aluminum strip with a width greater than the diameter of the stirring pin as the filler material during welding, and does not make the stirring pin contact the composite material plates on both sides during welding, so that the aluminum alloy and the composite material on both sides are driven to flow by the stirring action of the stirring pin in the aluminum strip to realize welding. Due to the strengthened material flow at the edge of the stirring pin, the aluminum clip strip and the composite material in the weld zone are uniformly mixed to become a composite material with a reinforcing phase, and the volume fraction of the reinforcing phase in the zone is slightly reduced. The method solves the problem that the high-volume-reinforced composite material cannot be welded, and can significantly improve the welding speed of the aluminum matrix composite material. The welding method has the advantages of simplicity, convenience and high efficiency.

Description

Technical Field

[0001] This invention relates to the field of metal welding technology, and more specifically to a welding method for high volume fraction particle-reinforced aluminum matrix composites. Background Technology

[0002] Aluminum-based composites possess advantages not found in single-metal materials, such as high specific strength, high specific modulus, and low thermal expansion. They have become important, even critical, materials in many high-tech fields, including aerospace, nuclear power, transportation, weaponry, and electronics. SiC particle-reinforced aluminum-based composites are currently the most widely used ceramic particle-reinforced composites. However, the significant differences in physical and chemical properties between SiC particles and the aluminum alloy matrix make the bonding of composites much more difficult than that of aluminum alloys, hindering the further development of aluminum-based composites. Current welding methods for composites include fusion welding, diffusion welding, and brazing. When welding composites using TIG, MIG, and LW, defects such as porosity, slag inclusions, cracks, and the brittle Al4C3 phase are easily generated, resulting in poor joint weld quality and low strength coefficients. When using diffusion welding on SiCp / Al composites, the oxide film often hinders atomic diffusion and prevents diffusion bonding between particles, severely affecting weld strength. During brazing, on the one hand, particles affect the wetting and spreading of the filler metal, easily leading to incomplete bonding and weak connection defects at particle aggregation points; on the other hand, the high welding temperature causes severe softening of the base material.

[0003] However, friction stir welding (FSW), as a solid-state joining method, has many advantages such as high quality, high efficiency, energy saving, no pollution, and high strength. It can effectively avoid the generation of melting defects and is an ideal welding method for aluminum-based composite materials. For example, Wang et al. used a cermet stir pin to perform FSW on 17% SiCp / 2009Al. The cermet stir pin could still drive the material to flow fully under high welding speed and obtained a defect-free weld joint. After post-weld heat treatment, the joint strength coefficient reached 97% of the base material. However, with the increase of SiC particle content, the plasticity of the composite material decreases sharply, the welding process window narrows, and the welding difficulty increases. On the other hand, with the increase of SiC particle content, the wear of the stir pin gradually worsens. Currently, the literature reports that the highest SiC volume fraction can be welded to composite materials, with a joint tensile strength of 166 MPa, which is only 50% of the base material. FSW is almost impossible for aluminum-based composite materials with higher volume fractions, and there are currently no relevant reports in the literature.

[0004] In summary, welding high-volume-fraction particle-reinforced aluminum matrix composites is challenging. Existing fusion welding methods struggle to avoid interparticle interface reactions and fusion-solidification defects, while FSW welding cannot prevent tool wear and is also unsuitable for welding high-volume-fraction particle-reinforced aluminum matrix composites. Therefore, it is essential to improve existing FSW processes and urgently develop a simple, convenient, and low-cost welding method to solve the welding difficulties of high-volume-fraction aluminum matrix composites and further expand the industrial applications of aluminum matrix composites. Summary of the Invention

[0005] The purpose of this invention is to provide a welding method for high volume fraction ceramic particle reinforced aluminum matrix composites. This method can reduce the wear of the stirring pin and obtain high-performance weld joints. At the same time, the process of this invention is simple, the production cost is low, the applicability is strong, and it is suitable for industrial promotion and application.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A welding method for high-volume-fraction ceramic particle-reinforced aluminum matrix composites is disclosed. This method employs friction stir welding, simultaneously using a needle-free welding tool I and a standard H13 steel welding tool II to weld the particle-reinforced aluminum matrix composite material. The method specifically includes the following steps:

[0008] (1) Determine the tool size of welding tool I according to the thickness of the plate to be welded. Welding tool I is a needleless welding tool.

[0009] (2) Welding tool II is designed according to the thickness of the plate to be welded. Welding tool II includes a shoulder and a stirring pin. The diameter of the shoulder is 3 to 5 times the thickness of the plate. The stirring pin is a special-shaped cylindrical threaded pin that can enhance the transverse material flow. The diameter of the root of the stirring pin is 1.0 to 1.5 times the thickness of the plate.

[0010] (3) Determine the width and thickness of the aluminum alloy clamping strip based on the thickness of the plate being welded and the diameter of the stirring pin;

[0011] (4) The surfaces of the plates to be welded and the clamp strips are mechanically ground and cleaned with alcohol or acetone. The aluminum alloy clamp strips are placed between the two composite material plates using a clamp. The aluminum alloy clamp strips are then rigidly fixed after being tightly placed with the composite material plates.

[0012] (5) Welding and sealing treatment of aluminum alloy strip and composite material plate by using welding tool I: The needleless welding tool I advances along the center line of the aluminum alloy strip to seal the aluminum alloy strip in the weld. The welding pressure is 0.05-0.1mm, the tool rotation speed is 100-300 rpm, and the welding speed is 200-500 mm / min.

[0013] (6) Welding is performed using welding tool II. Welding tool II moves in the same direction as welding tool I and moves along the center of the first weld until the welding is completed. The welding pressure is 0.1-0.2 mm, the tool rotation speed is 500-2000 rpm, and the welding speed is 100-1000 mm / min.

[0014] Preferably, the stirring pin of the welding tool II is made of low-cost ordinary tool steel (H13 steel), and its structure is an irregular cylindrical threaded pin. The diameter of the stirring pin is slightly smaller than the width of the aluminum alloy clamping bar. Compared with metal ceramic stirring pins, the cost of H13 steel stirring pin tools is reduced by an order of magnitude. This welding process can significantly improve the welding speed of aluminum-based composite materials.

[0015] Preferably, the irregular cylindrical threaded needle includes a cylindrical body and threads on the side of the body, and three strip-shaped protrusions are evenly distributed on the side of the cylindrical body. The strip-shaped protrusions are parallel to the axial direction of the cylindrical body and are at the same height as the cylindrical body. The outer side of the strip-shaped protrusion has a sharp corner (e.g., the cross-section of the strip-shaped protrusion (the cross-section along the radial direction of the cylindrical body) is designed as a triangle or an arc-shaped side triangle).

[0016] Preferably, in step (3), the clamping strip is of the same thickness as the plate being welded. In step (5) above, welding tool I is used for the first weld to ensure that the aluminum alloy clamping strip is sealed inside the weld and to prevent it from flying out during subsequent welding processes.

[0017] In step (6) above, the distance between the outer edge of the diameter of the stirring pin of welding tool II and the composite materials on both sides is L, and L is 0.05-0.1 times the diameter of the root of stirring pin II; the welding stirring pin does not contact the composite materials on both sides.

[0018] In step (6) above, the weld nugget area that ultimately forms the weld is a uniform fine-grained structure. Due to material rheology, the composite material and aluminum alloy are mixed to a certain extent, and the weld nugget area is also a composite material with a certain reinforcing phase.

[0019] The welding method of the present invention is applicable to the welding of high volume fraction (greater than 40%) particle-reinforced composite materials. The stirring pin material of the tool II used in friction stir welding is ordinary H13 steel.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. The friction stir bonding process involved in this invention belongs to solid-state welding technology. During the welding process, the material does not undergo melting and solidification, thus avoiding local defects such as segregation, porosity, hot cracking, and metallurgical defects that can occur in fusion welding. Compared with conventional FSW, the welding method involved in this invention can effectively achieve the welding of high volume fraction composite materials and obtain excellent mechanical properties.

[0022] 2. The welding tools involved in this invention are ordinary H13 steel tools, which are inexpensive, easy to process, and have a simple welding process.

[0023] 3. The stirring needle of the welding tool II designed in this invention is an irregular cylindrical threaded needle. Three strip-shaped protrusions are evenly distributed on the side of the cylindrical body of the irregular cylindrical threaded needle. This special structure of the welding tool can realize the welding of high volume fraction composite materials and obtain excellent mechanical properties.

[0024] 4. The welding method involved in this invention can significantly expand the welding window of high volume fraction aluminum-based composite materials, and has wide applicability to composite materials with various ceramic reinforcing phases. Welding parameters can be adjusted within a wider welding window to improve welding efficiency or joint quality.

[0025] 5. This invention is applicable to various friction stir welding machines. High-efficiency FSW can be achieved using traditional friction stir welding machines. This method improves production efficiency, greatly saves energy consumption and production costs, and is of great significance for expanding the industrial application of aluminum-based composite materials. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the high volume fraction composite material FSW of the present invention.

[0027] Figure 2 The diagram shows the structure of the stirring pin of welding tool II; where: (a) perspective view; (b) cross-sectional view; (c) post-weld wear condition.

[0028] Figure 3 The weld surface and microstructure in Example 1 are shown; wherein: (a) weld surface; (b) macroscopic morphology of weld; (c) weld nugget microstructure; (d) high magnification weld nugget microstructure.

[0029] Figure 4 The tensile results of the base material and weld in Example 1 are shown; where: (a) tensile curve; (b) weld tensile fracture location.

[0030] Figure 5 The surface and microstructure of the FSW weld of the metal-ceramic tool in Comparative Example 1; wherein: (a) weld surface; (b) macroscopic morphology of the weld; (c) weld nugget microstructure.

[0031] Figure 6 The wear condition of the metal-ceramic stirring pin after welding is shown; where: (a) before welding; (b) after welding.

[0032] Figure 7 The location of tensile fracture of the FSW weld in the comparative example of the metal-ceramic tool is shown. Detailed Implementation

[0033] To further understand the present invention, the present invention is described below with reference to examples. However, the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0034] This invention provides a design and welding process for friction stir welding of high volume fraction ceramic particle-reinforced aluminum matrix composites. The method first determines the size of the welding tool based on the plate thickness, then selects an aluminum alloy clamp strip with a width slightly larger than the diameter of the stirring pin as the weld filler material. The aluminum strip is then rigidly fixed between two composite material plates to be welded. First, a needleless welding tool I is used to seal the aluminum strip. Then, a self-designed irregular cylindrical stirring pin (made of ordinary H13 steel) is fully immersed in the aluminum strip for welding. The stirring pin does not contact the composite material plates on either side. The rotation of the stirring pin within the aluminum alloy clamp promotes intense transverse rheology of the material. The plasticized rheological aluminum alloy drives the surrounding composite material to flow, thereby achieving mixing and welding of the aluminum alloy and composite material. Due to the uniform mixing of the aluminum strip and composite material in the weld nugget area, the volume fraction of the reinforcing phase in the weld is slightly reduced. This method solves the problems of poor flowability of high volume composite materials and the inability to weld after the stirring pin wears out. Compared with the metal ceramic stirring pins commonly used in friction stir welding of aluminum matrix composites, the H13 steel stirring pin tool cost is reduced by an order of magnitude. This welding process can significantly improve the welding speed of aluminum matrix composites. The welding method involved has the advantages of simplicity, convenience and high efficiency.

[0035] In the following embodiments, the stirring needle of welding tool II is an irregularly shaped cylindrical threaded needle made of ordinary H13 steel. The irregularly shaped cylindrical threaded needle includes a cylindrical body and threads on the side of the body. Three strip-shaped protrusions are evenly distributed on the side of the cylindrical body, parallel to the axial direction of the cylindrical body and higher than the cylindrical thread. The outer side of each strip-shaped protrusion has a point (e.g., the cross-section of the strip-shaped protrusion (the section along the radial direction of the cylindrical body) is designed as a triangle or an arc-sided triangle). Figure 2 As shown.

[0036] Example 1

[0037] Two 2 mm thick SiCp / 6061 aluminum-based composite materials with a reinforcing phase volume fraction of 60% and 6061 aluminum alloy clamping strips with a cross-sectional width × thickness of 3.2 mm × 2 mm were used as the welding materials and fixed on the worktable. The aluminum alloy clamping strips were located between the two composite material plates and were tightly fitted.

[0038] The welding tool is used to weld along the center of the aluminum alloy clamping strip. The shoulder diameter of welding tool I is 8 mm, the downward pressure is 0.1 mm, the rotation speed of the welding tool is 200 rpm, and the welding speed is 200 mm / min. After welding, the aluminum alloy clamping strip is sealed in the weld.

[0039] Then, using welding tool II, with a shoulder diameter of 10mm, a stirring pin diameter of 3.0mm, a pin length of 1.8mm, a downward pressure of 0.15mm, and the outer edge of the stirring pin 0.1mm from the composite materials on both sides, welding is performed along the centerline of the aluminum alloy clamping strip. The welding speed is 2000rpm, and the travel speed is 1000mm / min. The welding diagram is shown below. Figure 1 As shown.

[0040] The cost of this irregularly shaped cylindrical stirring pin mainly includes material and processing costs, with each pin costing approximately 100 yuan. After welding, the H13 steel stirring pin shows almost no wear, such as... Figure 2 As shown. Microstructural analysis of the weld obtained in this embodiment revealed a smooth weld surface, a thinning of the weld zone, and no defects in the weld area. Due to the flow of the composite material driven by the aluminum alloy inserts, the two materials were fully mixed. A large number of reinforcing phase particles were also distributed within the weld nugget, with a volume fraction of 36% in the weld nugget area, which is 60% of the base material particle content. Figure 3 As shown. Mechanical property tests were performed on the weld obtained in this embodiment. The tensile strength of the joint was 202 MPa, reaching 88.2% of the strength of the base material (229 MPa). The joint ultimately fractured outside the heat-affected zone of the weld nugget, as shown. Figure 4 As shown.

[0041] Comparative Example 1

[0042] Two 2mm thick 60% SiCp / 6061Al sheets were fixed on the worktable as the weld material. A cermet stirring pin was used as the welding tool, and welding was performed along the center of the butt joint. The shoulder diameter was 10mm, the stirring pin diameter was 3.0mm, the pin length was 1.8mm, the pressure was 0.15mm, the welding speed was 500rpm, and the travel speed was 50mm / min. The weld surface was smooth and flat. A triangular region existed within the weld, with reinforcing phase particles concentrated at the edges of the triangle. The volume fraction of the reinforcing phase decreased within the triangular weld nugget. Figure 5 As shown. The material and processing costs of cermet stirring pins are much higher than those of H13 steel, with each pin costing approximately 1000 yuan. After welding, the stirring pins experience severe wear, shortening in length and rendering them unusable. Figure 6 As shown, this resulted in a significant weak bond defect at the bottom of the weld. Tensile testing of the weld revealed a tensile strength of only 150 MPa, far lower than that of the aluminum-based composite base material. Ultimately, tensile fracture occurred at the center of the weld nugget. Figure 7 As shown.

Claims

1. A method for friction stir welding of high volume fraction ceramic particle-reinforced aluminum matrix composites, characterized in that: This method uses H13 steel welding tools to weld aluminum alloy strips and simultaneously welds them to aluminum matrix composites on both sides; the H13 steel welding tools include welding tool I and welding tool II; in the high volume fraction ceramic particle reinforced aluminum matrix composite, the volume fraction of ceramic particles is greater than 40%; The method specifically includes the following steps: (1) Determine the tool size of welding tool I according to the thickness of the plate to be welded; the welding tool I is a needleless welding tool; the shoulder diameter of the welding tool I is 3 to 5 times the plate thickness, and the material is H13 steel; (2) Welding tool II is designed according to the thickness of the plate to be welded. Welding tool II includes a shoulder and a stirring pin. The diameter of the shoulder is 3 to 5 times the thickness of the plate, and the diameter of the root of the stirring pin is 1.0 to 1.5 times the thickness of the plate. The stirring pin of welding tool II is a special-shaped cylindrical threaded pin. The special-shaped cylindrical threaded pin includes a cylindrical body and threads on the side of the body. Three strip-shaped protrusions are evenly distributed on the side of the cylindrical body. The strip-shaped protrusions are parallel to the axial direction of the cylindrical body and higher than the threads on the side of the cylindrical body. The stirring pin of welding tool II is made of H13 steel. (3) Determine the width and thickness of the aluminum alloy clamping strip based on the thickness of the plate being welded and the diameter of the stirring pin; (4) The surfaces of the plates to be welded and the clamp strips are mechanically ground and cleaned with alcohol or acetone. The aluminum alloy clamp strips are placed between the two composite material plates using a clamp. The aluminum alloy clamp strips are then rigidly fixed after being tightly placed with the composite material plates. (5) Welding and sealing treatment of aluminum alloy strip and composite material plate by using welding tool I: The needleless welding tool I advances along the center line of the aluminum alloy strip to seal the aluminum alloy strip in the weld. The welding pressure is 0.05~0.1mm, the tool rotation speed is 100~300 rpm, and the welding speed is 200~500 mm / min. (6) Welding is performed using welding tool II. Welding tool II moves in the same direction as welding tool I and along the center of the first weld until the welding is completed. The welding pressure is 0.1~0.2mm, the tool rotation speed is 500-2000 rpm, and the welding speed is 100~1000 mm / min.

2. The friction stir welding method for high volume fraction ceramic particle reinforced aluminum matrix composites according to claim 1, characterized in that: In step (2), the outer side of the strip-shaped protrusion has a point, and the cross-section of the strip-shaped protrusion is designed as a triangle or an arc-shaped triangle.

3. The friction stir welding method for high volume fraction ceramic particle reinforced aluminum matrix composites according to claim 1, characterized in that: In step (3), the clamping strip is the same thickness as the plate being welded.

4. The friction stir welding method for high volume fraction ceramic particle reinforced aluminum matrix composites according to claim 1, characterized in that: In step (6) during the welding process, the stirring pin of welding tool II does not come into contact with the composite materials on both sides. It relies on the flow of aluminum alloy material to drive the flow of composite materials on both sides, thereby reducing the wear of the stirring pin.

5. The friction stir welding method for high volume fraction ceramic particle reinforced aluminum matrix composites according to claim 1, characterized in that: In step (6), when welding is performed using welding tool II, the distance between the outer edge of the stirring pin and the composite material is L, where L is 0.05 to 0.1 times the diameter of the stirring pin.

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