A SiC p Brazing method of / Mg composite materials

Abstract

A SiC p / Mg composite material brazing method, relates to a Mg-based composite material brazing method. The present invention aims to solve the current SiC p / Mg composite materials are difficult to wet and it is difficult to form effective joints under existing brazing processes. p The brazing material of / Mg composite material brazing has good wettability with the base material to be welded. p After intermittent pressure-assisted brazing of SiC / Mg composite materials, high-quality welded joints with good comprehensive performance were obtained. p The present invention performs intermittent pressure-assisted brazing in an atmospheric environment and uses the brazing material to weld SiC p / Mg composite materials were welded to obtain SiC p The welded components of the / Mg composite material and the brazing filler metal have tight joints, high joint strength and excellent welding effect.

Description

Technical Field

[0001] The invention relates to a brazing method for Mg-based composite materials. Background Art

[0002] SiC p / Mg composites (SiC p Reinforced magnesium matrix composites) have low density, high specific strength and specific stiffness, and excellent wear resistance. At present, squeeze casting SiC p / Mg composite materials have been increasingly used in the fields of automobile manufacturing, aerospace, etc. p The matrix alloy and reinforcement particles of the / Mg composite material have different specific gravity, and SiC particles are prone to agglomeration during traditional fusion welding, resulting in poor welding performance and SiC p The application of magnesium composite materials in many fields is limited. Brazing is very suitable for the connection of magnesium-based composite materials due to its low welding temperature. However, the smooth progress of the brazing process requires the brazing material to have good wettability to the base material. Due to the presence of SiC particles, the brazing material used for brazing magnesium alloys often has good wettability to SiC. p The wettability of SiC / Mg composites is not good, which is not conducive to the formation of joints and the joint strength is not ideal. This limits the p Therefore, a brazing process is simple, low-cost, and suitable for SiC p The brazing filler metal for brazing of magnesium / Mg composite materials has become an urgent problem to be solved in the field of magnesium-based composite welding. Summary of the Invention

[0003] The present invention aims to solve the current SiC p / Mg composite materials are difficult to wet and difficult to form effective joints under existing brazing processes. p Brazing method of / Mg composite materials.

[0004] SiC of the present invention p The brazing method of the / Mg composite material is carried out in the following steps:

[0005] 1. Preparation of solder: The solder composition by mass percentage is: 29% to 31% Al, 3% to 5% Zn, 0.5% to 1% Ti, and the balance is Mg. The specific preparation method is as follows:

[0006] S1. Weigh pure magnesium, pure zinc, pure aluminum, and Al-Ti master alloy as raw materials according to the mass percentage of each element in the solder; heat the pure magnesium, pure aluminum, and Al-Ti master alloy to 750°C to 780°C after mixing. After the solid materials are completely melted, keep the temperature and stand for 10 to 15 minutes to obtain a molten alloy liquid. Shielding gas is continuously introduced during the entire process;

[0007] S2. Cool the molten alloy liquid described in step S1 to 710° C. to 720° C., add the pure zinc block weighed in step S1, and then keep warm and stir continuously for 10 min to 15 min at a speed of 25 rpm to 30 rpm. Shielding gas is continuously introduced during the entire process.

[0008] S3. While maintaining stirring, cool the molten alloy to 490°C to 510°C, insert an ultrasonic rod preheated to 500°C to 520°C 10mm to 20mm below the surface of the molten alloy, with an ultrasonic frequency of 18kHz to 20kHz, an ultrasonic power of 1700W to 2100W, and an ultrasonic time of 8min to 15min. Shielding gas is continuously introduced during the entire process.

[0009] S4. After the ultrasonic wave is applied, the ultrasonic rod is removed and the solder is obtained after natural cooling and solidification. The protective gas is continuously introduced during the cooling process.

[0010] 2. Brazing process:

[0011] S1, SiC p The / Mg composite material was sequentially cleaned with deionized water, polished, ultrasonically cleaned with acetone, and cleaned with anhydrous ethanol, and then dried to obtain the base material to be welded;

[0012] S2. Cut the solder prepared in step 1 according to the size of the base material to be welded, then polish the surface of the solder, ultrasonically clean it in an acetone solution, and naturally dry it to obtain the solder to be used;

[0013] S3. Assemble two base materials to be welded and the brazing filler metal to be used in a sandwich structure, wrap them with three layers of aluminum foil to obtain a sample to be welded, and perform intermittent pressure-assisted brazing in an atmospheric environment;

[0014] The intermittent pressure assisted brazing process is:

[0015] ①. The heating rate is 25℃ / min~30℃ / min, the welding temperature is 460℃~490℃, and the heat preservation is carried out for 10min~15min.

[0016] ② Then apply pressure of 25MPa to 30MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 20s to 60s. This process is carried out at 460℃ to 490℃.

[0017] ③. Repeat the process of ② for a total of 2 to 3 minutes, and then air cool to obtain SiC p / Welded components of AZ91 composite material and brazing filler metal.

[0018] The first aspect of the present invention provides a method for brazing SiC p The solder of the composite material of SiC is composed of Mg-Al-Zn-Ti mixed solder, in which Mg is used as the matrix and the amount of Al added is selected to be 29% to 31%, which is near the Mg-Al eutectic composition. This can reduce the melting point of the solder, increase the fluidity of the solder, and at the same time increase the strength and hardness of the solder. The amount of Zn added is selected to be 3% to 5%, which can further increase the strength of the solder and improve the fluidity of the solder. The amount of Ti added is selected to be 0.5% to 1%, which can improve the bonding strength between the solder and SiC. p The contact surface tension of the / Mg composite material helps to improve the wettability of the brazing filler metal to the base material, improves the bonding strength between the brazing filler metal and the base material, and thus improves the strength of the brazed joint to obtain a high-quality welded joint. The brazing filler metal has uniform composition, dense structure, high activity, simple preparation process, high production efficiency, and is suitable for automated production. It can be widely used in SiC p / Mg composite materials and other magnesium-based composite materials brazing field.

[0019] The second aspect of the present invention provides a method for welding SiC p A method for preparing a brazing filler metal of a SiC / Mg composite material comprises the following steps: heating and melting Mg, Al, Zn, and Al-Ti alloy in a protective gas atmosphere, applying stirring and ultrasonic homogenization to the alloy to prevent component segregation; and cooling the alloy directly in a crucible to avoid the introduction of impurities during the pouring process and to avoid defects such as pores and slag inclusions. The method is simple in process and easy to operate, and can obtain an alloy brazing filler metal with excellent performance for SiC p Brazing of Mg / Mg composite materials is suitable for wide promotion.

[0020] The third aspect of the present invention provides a method for welding SiC p The method for using the brazing filler metal of the SiC / Mg composite material comprises the following steps: cleaning, grinding, ultrasonic cleaning, etc. the SiC / Mg composite material and the brazing filler metal are respectively subjected to treatments such as cleaning, grinding, ultrasonic cleaning, etc., the brazing filler metal to be used and the sample to be welded are assembled into a sandwich structure, and intermittent pressure-assisted brazing is performed under atmospheric conditions. The brazing filler metal is used to weld the SiC / Mg composite material. p / Mg composite materials were welded to obtain SiCp The welded components of the Mg composite material and the brazing filler metal have tight joints, high joint strength and excellent welding effect. The aluminum foil wrapping effectively prevents oxidation and burning of the magnesium-based composite material, applies intermittent pressure, reduces the weld width, makes the weld consistent with the parent material composition, and removes the oxide film inside the weld caused by the melting of the brazing filler metal, and prevents the agglomeration of silicon carbide particles.

[0021] The role of intermittent pressure in the present invention:

[0022] First, during the welding process, element diffusion will occur between the liquid solder and the solid base material, forming a large amount of low-melting-point eutectic structure and generating a large amount of brittle intermetallic compounds. Brittle intermetallic compounds are the weakest part of the entire weld. A large amount of continuously distributed intermetallic compounds will have an adverse effect on the mechanical properties of the joint.

[0023] Second, the base material used in the present invention is composed of a matrix magnesium alloy and a reinforcing phase silicon carbide. During the welding process, the brazing filler metal reacts with the surface of the base material and is dissolved, and the silicon carbide particles are released and enter the weld. As the amount of silicon carbide gradually increases, silicon carbide particles are likely to agglomerate at the weld during the solidification process, which will eventually seriously affect the mechanical properties of the joint.

[0024] Third, during the welding process, a continuous oxide film will form on the surface of the solder, preventing the solder from contacting the base material.

[0025] To address these issues, applying pressure can break down the continuous oxide film, allowing the filler metal to contact the base metal while squeezing out the liquid metal within the weld, creating a narrow-gap weld with a width reduced to tens of microns. This helps prevent the formation of large quantities of continuous intermetallic compounds and the agglomeration of silicon carbide particles. Intermittent application of pressure can, on this basis, repeatedly break down the oxide film produced during welding and squeeze it out of the weld, reducing residual oxides in the weld. Intermittent pressure also ensures the continuous flow of liquid filler metal in the joint, preventing compositional segregation and making the joint structure more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 SiC used in step 2 of experiment 1 p Metallographic diagram of / Mg composite material;

[0027] Figure 2 This is the metallographic image of the weld obtained in test 5;

[0028] Figure 3 This is a photo of the base material after brazing in Test 5. DETAILED DESCRIPTION

[0029] Specific embodiment 1: This embodiment is a SiCp The brazing method of the / Mg composite material is specifically carried out according to the following steps:

[0030] 1. Preparation of solder: The solder composition by mass percentage is: 29% to 31% Al, 3% to 5% Zn, 0.5% to 1% Ti, and the balance is Mg. The specific preparation method is as follows:

[0031] S1. Weigh pure magnesium, pure zinc, pure aluminum, and Al-Ti master alloy as raw materials according to the mass percentage of each element in the solder; heat the pure magnesium, pure aluminum, and Al-Ti master alloy to 750°C to 780°C after mixing. After the solid materials are completely melted, keep the temperature and stand for 10 to 15 minutes to obtain a molten alloy liquid. Shielding gas is continuously introduced during the entire process;

[0032] S2. Cool the molten alloy liquid described in step S1 to 710° C. to 720° C., add the pure zinc block weighed in step S1, and then keep warm and stir continuously for 10 min to 15 min at a speed of 25 rpm to 30 rpm. Shielding gas is continuously introduced during the entire process.

[0033] S3. While maintaining stirring, cool the molten alloy to 490°C to 510°C, insert an ultrasonic rod preheated to 500°C to 520°C 10mm to 20mm below the surface of the molten alloy, with an ultrasonic frequency of 18kHz to 20kHz, an ultrasonic power of 1700W to 2100W, and an ultrasonic time of 8min to 15min. Shielding gas is continuously introduced during the entire process.

[0034] S4. After the ultrasonic wave is applied, the ultrasonic rod is removed and the solder is obtained after natural cooling and solidification. The protective gas is continuously introduced during the cooling process.

[0035] 2. Brazing process:

[0036] S1、SiC p The / Mg composite material was sequentially cleaned with deionized water, polished, ultrasonically cleaned with acetone, and cleaned with anhydrous ethanol, and then dried to obtain the base material to be welded;

[0037] S2. Cut the solder prepared in step 1 according to the size of the base material to be welded, then polish the surface of the solder, ultrasonically clean it in an acetone solution, and naturally dry it to obtain the solder to be used;

[0038] S3. Assemble two base materials to be welded and the brazing filler metal to be used in a sandwich structure, wrap them with three layers of aluminum foil to obtain a sample to be welded, and perform intermittent pressure-assisted brazing in an atmospheric environment;

[0039] The intermittent pressure assisted brazing process is:

[0040] ①. The heating rate is 25℃ / min~30℃ / min, the welding temperature is 460℃~490℃, and the heat preservation is carried out for 10min~15min.

[0041] ② Then apply pressure of 25MPa to 30MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 20s to 60s. This process is carried out at 460℃ to 490℃.

[0042] ③. Repeat the process of ② for a total of 2 to 3 minutes, and then cool in air to obtain SiC p / Welded components of AZ91 composite material and brazing filler metal.

[0043] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the master alloy Al-Ti in step 1 has a Ti content of 4% to 6% by mass. Other aspects are the same as specific embodiment 1.

[0044] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the protective gas in step 1 is a mixture of CO2 and SF6, wherein the volume fraction of SF6 is 5% to 6%. Other aspects are the same as specific embodiment 1 or 2.

[0045] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that in step 2 S2 , the solder prepared in step 1 is cut into pieces with a thickness of 0.5 mm to 1 mm. Other aspects are the same as specific embodiments 1 to 3.

[0046] Specific embodiment 5: This embodiment differs from specific embodiment 4 in that the thickness of the aluminum foil in step 2 is 20 μm. Other aspects are the same as specific embodiment 4.

[0047] Specific embodiment 6: This embodiment differs from the specific embodiment 5 in that: the SiC p The particle size of SiC particles in the / Mg composite material is 5 μm to 10 μm, the volume fraction is 10% to 12%, and the matrix alloy is AZ91 magnesium alloy. Other aspects are the same as those in the fifth embodiment.

[0048] The present invention is verified by the following test:

[0049] Test 1: This test is a SiC p The brazing method of the / Mg composite material is specifically carried out according to the following steps:

[0050] 1. Preparation of solder: The solder composition by mass percentage is: 31% Al, 3% Zn, 0.25% Ti, and the balance is Mg. The specific preparation method is as follows:

[0051] S1. Weigh pure magnesium, pure zinc, pure aluminum, and an Al-Ti master alloy according to the mass percentage of each element in the solder; heat the pure magnesium, pure aluminum, and Al-Ti master alloy to 750°C after mixing. After the solid materials are completely melted, keep the mixture at this temperature and allow it to stand for 10 minutes to obtain a molten alloy liquid. Shielding gas is continuously introduced during the entire process. The mass percentage of Ti in the Al-Ti master alloy is 5%.

[0052] S2. Cool the molten alloy liquid described in step S1 to 710° C., add the pure zinc block weighed in step S1, and then keep warm and stir continuously for 10 minutes at a speed of 25 r / min. Continuously introduce protective gas during the entire process;

[0053] S3. While stirring, cool the molten alloy to 490°C, insert an ultrasonic rod preheated to 500°C 10 mm below the surface of the molten alloy, set the ultrasonic frequency to 18 kHz, the ultrasonic power to 1700 W, and the ultrasonic time to 8 minutes. Shielding gas is continuously introduced during the entire process.

[0054] S4. After the ultrasonic wave is applied, the ultrasonic rod is removed and the solder is obtained after natural cooling and solidification. The protective gas is continuously introduced during the cooling process.

[0055] The protective gas in step 1 is a mixture of CO2 and SF6, wherein the volume fraction of SF6 is 5% to 6%;

[0056] 2. Brazing process:

[0057] S1、SiC p The SiC / Mg composite material was sequentially cleaned with deionized water, polished, ultrasonically cleaned with acetone for 30 minutes, and cleaned with anhydrous ethanol, and dried to obtain the base material to be welded; p The particle size of SiC particles in the / Mg composite material is 5μm to 10μm, the volume fraction is 10%, and the matrix alloy is AZ91 magnesium alloy; the SiC p The specification of the / Mg composite material is a sheet material of 30mm×30mm×3mm;

[0058] S2. Cut the solder prepared in step 1 into a thickness of 0.5 mm according to the size of the base material to be welded, then polish the surface of the solder, ultrasonically clean it in an acetone solution, and naturally dry it to obtain the solder to be used;

[0059] S3. Assemble two base materials to be welded and the brazing filler metal to be used in a sandwich structure, wrap them with three layers of aluminum foil to obtain a sample to be welded, and perform intermittent pressure-assisted brazing in an atmospheric environment;

[0060] The intermittent pressure assisted brazing process is:

[0061] ①. The heating rate is 30℃ / min, the welding temperature is 460℃, and the temperature is kept at 15 minutes.

[0062] ② Then apply pressure of 25MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 30s. This process is carried out at 460℃.

[0063] ③. Repeat the process of ② for a total of 2 minutes, and obtain SiC after air cooling. p / Welded components of AZ91 composite material and brazing filler metal.

[0064] The maximum shear strength of the joint at room temperature in test 1 is 52.7 MPa.

[0065] Experiment 2: This experiment differs from Experiment 1 in that:

[0066] The solder in step 1 is composed of 30% Al, 4% Zn, 0.5% Ti, and the balance Mg in terms of mass percentage.

[0067] The intermittent pressure assisted brazing process described in S3 of step 2 is:

[0068] ①. The heating rate is 30℃ / min, the welding temperature is 470℃, and the temperature is kept at 15 minutes.

[0069] ② Then apply pressure of 25MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 40s. This process is carried out at 470℃.

[0070] The rest is the same as Experiment 1.

[0071] The maximum shear strength of the joint at room temperature in test 2 is 56.7 MPa.

[0072] Experiment 3: This experiment differs from Experiment 1 in that:

[0073] The solder described in step 1 is composed of 31% Al, 4% Zn, 0.5% Ti, and the balance Mg in terms of mass percentage;

[0074] The intermittent pressure assisted brazing process described in S3 of step 2 is:

[0075] ①. The heating rate is 30℃ / min, the welding temperature is 480℃, and the temperature is kept at 15 minutes.

[0076] ② Then apply pressure of 28MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 15s. This process is carried out at 480℃.

[0077] The rest is the same as Experiment 1.

[0078] The maximum shear strength of the joint at room temperature in test three is 54.3 MPa.

[0079] Test 4: This test differs from Test 1 in that:

[0080] The solder described in step 1 is composed of 29% Al, 5% Zn, 1% Ti, and the balance Mg in terms of mass percentage;

[0081] The intermittent pressure assisted brazing process described in S3 of step 2 is:

[0082] ①. The heating rate is 30℃ / min, the welding temperature is 490℃, and the temperature is kept at 15 minutes.

[0083] ② Then apply pressure of 28MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 20s. This process is carried out at 490℃.

[0084] The rest is the same as Experiment 1.

[0085] The maximum shear strength of the joint in test 4 at room temperature is 60.1 MPa.

[0086] Test 5: This test differs from Test 1 in that:

[0087] The solder described in step 1 is composed of 30% Al, 4% Zn, 0.75% Ti, and the balance Mg in terms of mass percentage;

[0088] The intermittent pressure assisted brazing process described in S3 of step 2 is:

[0089] ①. The heating rate is 30℃ / min, the welding temperature is 480℃, and the temperature is kept at 15 minutes.

[0090] ② Then apply pressure of 30MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 20s. This process is carried out at 480℃.

[0091] The rest is the same as Experiment 1.

[0092] The maximum shear strength of the joint at room temperature in test four is 64.6 MPa.

[0093] Figure 1SiC used in step 2 of experiment 1 p A metallographic image of a magnesium / Mg composite reveals 5μm to 10μm silicon carbide particles distributed within a magnesium alloy matrix. While having a density similar to that of magnesium alloys, magnesium-based composites possess a range of exceptional physical and mechanical properties, including higher hardness, specific strength, elastic modulus, excellent wear resistance, and good dimensional stability. Magnesium-based composites are suitable for large-scale engineering applications due to their simple preparation process, low cost, good machinability, and uniform and highly isotropic particle dispersion within the material. Uniform dispersion of reinforcement particles at the matrix grain boundaries hinders grain boundary sliding and pins dislocations, enhancing creep resistance. The interface between the particles and the metal matrix effectively transfers applied loads to the high-hardness, high-strength particles, thereby enhancing the overall strength of the material. The combination of hard particles and soft metal contributes to both enhanced strength and excellent fracture toughness, making them suitable for widespread use in more demanding service environments.

[0094] Figure 2 The metallographic image of the weld obtained in Test 5 shows an extremely small weld width. This is primarily due to the 2-minute intermittent pressure extruding a large amount of eutectic liquid phase within the weld. Eutectic structure and intermetallic compounds are not observed within the weld. The weld structure is essentially consistent with that of the base metal. The SiC particles are evenly dispersed within the weld, with no agglomeration observed. The degree of dispersion is essentially consistent with the original base metal structure, primarily due to the continuous intermittent pressure that constantly prevents SiC particle agglomeration. These evenly distributed SiC particles play a crucial role in improving weld strength.

[0095] Figure 3 This is a photo of the base material after brazing in test 5. It can be seen that the base material is intact and no burn damage occurs.

Claims

1. A SiC p / Mg composite material brazing method, characterized in that SiC p The brazing method of the / Mg composite material is carried out in the following steps:

1. Preparation of solder: The solder composition by mass percentage is: 29% to 31% Al, 3% to 5% Zn, 0.5% to 1% Ti, and the balance is Mg. The specific preparation method is as follows: S1. Weigh pure magnesium, pure zinc, pure aluminum, and Al-Ti master alloy as raw materials according to the mass percentage of each element in the solder; heat the pure magnesium, pure aluminum, and Al-Ti master alloy to 750°C to 780°C after mixing. After the solid materials are completely melted, keep the temperature and stand for 10 to 15 minutes to obtain a molten alloy liquid. Shielding gas is continuously introduced during the entire process; S2. Cool the molten alloy liquid described in step S1 to 710° C. to 720° C., add the pure zinc block weighed in step S1, and then keep warm and stir continuously for 10 min to 15 min at a speed of 25 rpm to 30 rpm. Shielding gas is continuously introduced during the entire process. S3. While maintaining stirring, cool the molten alloy to 490°C to 510°C, insert an ultrasonic rod preheated to 500°C to 520°C 10mm to 20mm below the surface of the molten alloy, with an ultrasonic frequency of 18kHz to 20kHz, an ultrasonic power of 1700W to 2100W, and an ultrasonic time of 8min to 15min. Shielding gas is continuously introduced during the entire process. S4. After the ultrasonic wave is applied, the ultrasonic rod is removed and the solder is obtained after natural cooling and solidification. The protective gas is continuously introduced during the cooling process.

2. Brazing process: S1、SiC p The / Mg composite material was sequentially cleaned with deionized water, polished, ultrasonically cleaned with acetone, and cleaned with anhydrous ethanol, and then dried to obtain the base material to be welded; S2. Cut the solder prepared in step 1 according to the size of the base material to be welded, then polish the surface of the solder, ultrasonically clean it in an acetone solution, and naturally dry it to obtain the solder to be used; S3. Assemble two base materials to be welded and the brazing filler metal to be used in a sandwich structure, wrap them with three layers of aluminum foil to obtain a sample to be welded, and perform intermittent pressure-assisted brazing in an atmospheric environment; The intermittent pressure assisted brazing process is: ①. The heating rate is 25℃ / min~30℃ / min, the welding temperature is 460℃~490℃, and the heat preservation is carried out for 10min~15min. ② Then apply pressure of 25MPa to 30MPa intermittently for T1, and then remove the pressure for T2, where T1 is equal to T2 and T1 is 20s to 60s. This process is carried out at 460℃ to 490℃. ③. Repeat the process of ② for a total of 2 to 3 minutes, and then air cool to obtain SiC p / Welded components of AZ91 composite material and brazing filler metal.

2. A SiC according to claim 1 p / Mg composite material brazing method, characterized in that The master alloy Al-Ti described in step 1 has a Ti content of 4% to 6% by mass.

3. The SiC according to claim 1 p / Mg composite material brazing method, characterized in that The protective gas in step 1 is a mixed gas of CO2 and SF6, wherein the volume fraction of SF6 is 5% to 6%.

4. The SiC according to claim 1 p / Mg composite material brazing method, characterized in that In step 2 S2, the solder prepared in step 1 is cut into pieces with a thickness of 0.5 mm to 1 mm.

5. The SiC according to claim 1 p / Mg composite material brazing method, characterized in that The thickness of the aluminum foil in step 2 is 20 μm.

6. The SiC according to claim 1 p / Mg composite material brazing method, characterized in that SiC as described in step 2 p The particle size of SiC particles in the SiC / Mg composite material is 5 μm to 10 μm, the volume fraction is 10% to 12%, and the matrix alloy is AZ91 magnesium alloy.

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