| The rapid development of high-power IGBT modules is also companied by increasing demand for substrate packaging materials with excellent performance.Among many electronic packaging materials,high volume fraction SiCp/Al composites has extremely important application prospects due to their high hardness,thermal conductivity and flexural strength,low thermal expansion c oefficient and density.In this experiment,a 60%volSiCp/2024Al composite was prepared by the self-developed direct thermal powder thixoforming technique,the thermophysical properties such as hardness,flexural strength and other mechanical and thermal exp ansion coefficients and thermal conductivity of the composites were investigated through the treatment of the morphology of silicon carbide particles and the heat treatment of composite material.In this paper,optical microscopy?OM?,scanning electron microscopy?SEM?,phase analysis?XRD?were used to observe the microstructure and composition of the composites,and the strength and thermophysical properties of the composites were characterized.,the morphology treatment process of silicon carbide particles and the influence of morphology change on the properties of composite materials were studied in this experiment.Meanwhile,the influence of heat treatment process of composite materials on the properties of composites was investigated.Main achievements are listed below:The silicon carbide particles are first oxidized at a high temperature of 1100?for3h,Secondly,the 10%HF pickling ball milling process were used to study the ball-to-batch ratio,ball diameter ratio and shaping time of the shaping process to obtain the best silicon carbide particle shaping process.The result showed that the ball-to-batch ratio was 1.5:1;the Si3N4 ceramic ball diameter ratio was 1.2mm:0.8mm:0.5mm=2:3:5;shaping time is 10h;rotation speed is 96r/min.The sharp corners of the shaped silicon carbide particles are effectively passivated,and the particles become more nearly spherical.The optimum particle roundness is 0.825 and the aspect ratio is 1.306.Agglomeration phenomenon of the microstructured silicon carbide particles was not observed on the 60vol%SiCp/2024Al composite prepared by the direct thermal powder thixoforming technique,and the uniform dispersion is distributed on the aluminum matrix,and the reinforcing phase particles are relatively complete.It is relatively clean,and the reinforcing phase is well bonded to the substrate without obvious holes.It can be seen from the composition analysis that there is no formation of the Al4C3 heterophase in the composite.The relative density of SiCp/2024Al composites prepared by silicon carbide particles after shaping is higher than that of original silicon carb ide particles.The relative density of SiCp/2024Al composites treated by 5h,10h and 15h is higher than that of unshaped SiCp/2024Al.The relative density of the composites increased by2.14%,2.66%,and 2.68%.The particle morphology has a significant eff ect on the thermal expansion coefficient and thermal conductivity of SiCp/2024Al composites.After the silicon carbide particles are shaped,the thermal expansion coefficient of the composites is effectively reduced,and the temperature range is controlled at 4.2×10-6/K9.8×10-6/K in the temperature range of 25°C350°C.the thermal conductivity of the composite material was greatly improved,which was 21.7%higher than t he original state,reaching 197W/?m·K?.It is also proved that the Turner model can be u sed to predict the CTE of high volume fraction composites,and the improved H-Jprediction model is suitable for the thermal conductivity of biphasic particle reinforced metal matrix composites.Suitable heat treatment can improve the mechanical properties of SiCp/2024Al composites,it can further reduce the thermal expansion coefficient of composites and improve the thermal conductivity of composites.With the increase of solution temperature and solution time.the best heat treatment process is obtained:Wh en the solution temperature is 505?and the solution time is 2h,and the flexural strength and hardness of the composite reach 396MPa and 167HBS.When the artificial aging temperature is 190°C and the aging time is 20h,and the flexural strength and hardness of the composite reach a peak of 425MPa and 234HBS.The thermal expansion coefficient of the composite material is controlled between 3.8×10-6/K9.1×10-6/K in the temperature range of 25°C350°C.The thermal conductivity of the composite material is increased by 20.3%and 24.7%respectively.Reaching 202W/?m?K?.The study of the overall density and hardness distribution of SiCp/2024Al composites showed that the properties of the composites were basically consistent,indicating that the temperature and pressure distribution of the composites were uniform during the forming process.Meanwhile,the changes of density,hardness,flexural strength and thermal expansion coefficient of SiCp/2024Al composites prepared under the same conditions were studied in detail.The results show that the performance difference of the six SiCp/2024Al composites is small.All performance is within the allowance tolerance in error,it is further pointed out that the direct thermal method powder thixoforming technology process parameters are relatively mature and stable,and the process conditions for the trial production of composite materials are already available. |
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