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Vacuum Heat Treatment Furnace

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Aluminum alloy micro-channel cooling plate vacuum gas quenching

1.Process introduction

With the rapid development of electronic technology and the integration of electronic products, the power of aerospace, military and civil electronic equipment continues to increase. and increased sharply. Studies have shown that for every 10 ℃ increase in temperature of a single electronic component, its failure rate will double, and the corresponding reliability will be reduced by half. Therefore, the heat dissipation of electronic devices has inevitably become one of the key factors restricting the fields of electronic information and aerospace.

Traditional air cooling is only suitable for low heat flux density, and the system is more complicated and is not conducive to safe operation; the use of general copper and aluminum for heat conduction is also not suitable for electronic equipment with high heat flux density. Because the micro-channel radiator is an integral structure without moving parts, its performance is relatively stable, and the manufacturing cost is low, and it has broad application prospects in the field of heat dissipation of electronic components. The structure of the micro-channel radiator is generally to directly process the flow channel on the silicon wafer, copper or aluminum alloy plate and add a cover plate on it. The micro-channel radiator was first proposed by Tuckerman and Pease in 1981. The core idea is to add micro-scale channels at the bottom of electronic devices, and the heat will be taken away by convective heat transfer when the fluid flows through the micro-channel.

Due to the low cost, light weight, corrosion resistance and excellent thermal conductivity of aluminum alloys, in recent years, many research institutions have proposed using aluminum alloys to fabricate micro-channel radiators. Based on the functionality of the aluminum alloy micro-channel structure, it is required that each channel and the cover plate be tightly connected with small deformation. The commonly used connection method at present is brazing, mainly vacuum brazing and gas shielded brazing. Soldering needs to use flux to remove the oxide film, so it is difficult to use gas shielded brazing for the connection between the internal ribs of the flow channel and the cover plate. Welding is widely used. However, the key problems existing in vacuum brazing are as follows: (1) The micro-channel space is small, and the brazing material is easy to flow into the channel, which hinders the flow of the working medium and affects the heat dissipation performance; (2) There is a large gap between the solder and the base metal. Due to the difference in composition, the radiator will cause electrochemical corrosion and weld cracking during long-term service; 3. During the use of the micro-channel radiator, a large internal pressure will be generated with the change of the temperature of the working medium, and the joints are required to have high The strength of the brazed joint is easy to exist, and the unwelded defect is easy to cause the joint strength to decrease.

Diffusion welding is to contact the welding surfaces of two metal parts to be welded under a certain temperature and pressure, and expand the physical contact of the surfaces to be welded through microscopic plastic deformation or through the generation of a small amount of liquid phase on the welding surface. Atomic diffusion, mutual penetration, a welding method to achieve metallurgical bonding. Since the microstructure of the diffusion welded joint is close to that of the base metal, the joint has high strength, strong corrosion resistance, stable quality and high pass rate. The 6063 aluminum alloy micro-channel radiator sample was welded by vacuum diffusion welding. The deformation of the flow channel was effectively controlled by designing different down pressures. The deformation of the flow channel after diffusion welding was observed. The microstructure and interfacial bonding force of aluminum alloy diffusion welding interface, as well as the effects of different down pressures (0.2 mm, 0.5 mm, 0.7 mm) on the microstructure and mechanical properties of diffusion welded joints. At the same time, the vacuum gas quenching treatment was carried out on the diffusion welded joint, and the differences in the microstructure and properties of the diffusion welded joint before and after vacuum gas quenching were compared and analyzed.

2.Test method

The diffusion welding test is carried out in a high-pressure vacuum diffusion welding furnace. The diffusion welding temperature is 520 ~ 540 ℃, the diffusion welding holding time is 90min, the diffusion welding pressure is 10 ~ 25 kN, the vacuum degree is ≥1 × 10-3Pa, and the diffusion welding sample is The amount of downward pressure is 0.2 mm, 0.5 mm, and 0.7 mm, respectively. Part of the diffusion welding samples were subjected to vacuum vacuum gas quenching treatment. The vacuum vacuum gas quenching parameters were: solution treatment at 520 ~ 540 ℃ for 2 ~ 2.5 h, and artificial aging at 180 ~ 200 ℃ for 4 ~ 6 h.

A number of joint bars were cut from both sides of the post-weld sample by wire cutting, and a part was made into a metallographic sample. The microstructure of the diffusion welded joint was analyzed by optical microscope, scanning electron microscope and energy spectrum analysis tester; Another part of the bar material was processed into tensile samples, and the tensile strength was tested. To ensure the accuracy of the results, six groups of samples were welded for each parameter, and the average value was taken as the final result, and the fracture structure and morphology were observed at the same time.

3.The effect of vacuum gas quenching on the microstructure and properties of the joint

Because the 6063 aluminum alloy is a heat-treatable strengthened aluminum alloy, and the size of the strengthening phase after diffusion welding increases, the distribution is uneven, and there is segregation, which leads to a significant decrease in the mechanical properties of the material after diffusion welding. In order to improve the mechanical properties of the base metal and the joint and avoid large deformation, it is decided to perform vacuum gas quenching on the brazed samples (compared to water quenching and oil quenching, the cooling rate is smaller, and the vacuum gas quenching test The sample deformation is smaller), and now the vacuum gas quenching treatment is performed on the diffusion welded joint under the condition of the down pressure of 0.5 mm. The energy spectrum analysis of the microstructure of the diffusion welded joint before and after vacuum gas quenching shows that the atomic ratio of Mg and Si is close to 2:1, which is determined as Mg, Si strengthening phase. The phase is not fully solutionized and the relative size is coarse, and there is a tendency to aggregate and grow into long strips; the process parameters of solution treatment at 520 ~ 540 ℃ for 2 ~ 2.5 h, and artificial aging at 180 ~ 200 ℃ for 4 ~ 6 h are used for diffusion welding. After vacuum gas quenching of the joint, the size of the strengthening phase is obviously smaller and the distribution is more uniform, which is beneficial to the improvement of the mechanical properties of the joint. However, the coarsening phenomenon caused by the residual and insufficient solid solution strengthening phase can also be observed on the aluminum alloy base metal and the diffusion welding interface, indicating that the cooling rate of the vacuum gas quenching process itself is slower than that of water quenching and oil quenching. , the degree of solid solution is relatively weak, and it is difficult to achieve sufficient solid solution and precipitation of the strengthening phase. Therefore, a more sufficient solid solution effect can be achieved by further optimizing the vacuum air quenching process parameters.

The Rockwell hardness test was carried out on the diffusion welded joint after vacuum gas quenching, and the average hardness was 98.6 HRL, which was 26.1% higher than that before vacuum gas quenching. The tensile strength of the diffusion welded joint after vacuum air quenching was tested. The test results are shown in the figure below. It can be seen from the figure that the tensile strength of the diffusion welded joint after vacuum gas quenching increased from 84.5 MPa to 186.5 MPa.

4.Conclusion

(1) Vacuum diffusion welding can realize the reliable connection of 6063 aluminum alloy micro-channel, and the side wall of the channel has a thick phenomenon after diffusion welding. When the downward pressure is 0.2 mm, the phenomenon of pier thickening is not obvious; when the downward pressure reaches 0.7 mm, the runner is greatly deformed. Therefore, it is necessary to reasonably design the size of the runner and strictly control the downward pressure before diffusion welding.

(2) When the diffusion welding temperature is 520 ~ 540 ℃, the holding time is 90min, and the pressing amount is 0.5 mm, the diffusion welding interface can obtain a uniform, continuous and dense structure, and the average tensile strength of the joint is as high as 84.5MPa, reaching More than 90% of the tensile strength of the base metal after welding.

(3) After the vacuum gas quenching of the diffusion welded samples, the average hardness increased from 78.2 HRL to 98.6 HRL, which could reach more than 85% of the hardness of the base metal of 6063 aluminum alloy; the tensile strength of the joints increased from 84.5 MPa to 186.5 MPa. Compared with water quenching and oil quenching, the cooling rate of vacuum gas quenching process is slower, and the degree of solid solution is relatively weaker. More sufficient solid solution effect.

Selection of vacuum gas quenching equipment: RVGQ series vacuum gas quenching furnaces produced by SIMUWU are high-quality products for vacuum heat treatment of tools and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum gas quenching process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing.