The Research On The Properties Of High Volume Fraction SiC_p/6061Al Composites Fabricated By Direct Electrothermal Powder Thixoforming

High volume fraction SiC_p/Al composites have the advantages of high strength,highhardness,smallthermalexpansioncoefficientandgoodthermal conductivity,have been widely used in electronic packaging industry.The traditional preparation methods of SiC_p/Al composites has poor wettability between the particles and the matrix,uneven distribution of particles in the matrix and prone to interfacial reaction,which has an adverse effect on the properties of the composites,and makes it difficult to achieve industrial mass production.In this paper,the 60%volume fraction of SiC particle reinforced 6061aluminum matrix composites were prepared by direct electrothermal powder thixoforming.The main research contents are as follows:through scanning electron microscope and XRD detection methods,observe the interface state of composite materials,analyze the formation of interfacial reaction products.Pretreat SiC particles,including hydrochloric acid immersion,high temperature oxidation,pickling and ball milling.The effects of pretreatment on the surface morphology and properties of SiC particles were studied.The SiC composite after surface modification is made into SiC_p/Al composite,and its mechanical properties and thermophysical properties were examined to determine the best pretreatment process.The SiC_p/Al composites were subjected to solution heat treatment for aging,and the effect of aging time on the precipitated phase of the matrix material was investigated.The optimum heat treatment process was determined by testing the properties of the SiC_p/Al composite.The results indicate that:?1?SiC_p/6061Alcompositespreparedby directelectrothermalpowder thixoforming process,when the molding temperature is 610°C,the distribution of reinforcement particles in the matrix is relatively uniform,the interface between SiC particles and aluminum matrix is well,and the impurity phase or new phase is not detected,which indicates that there is none interfacial reaction occurred during the molding process.Finally,the flexural strength of SiC_p/6061Al composites was187.45 MPa and the cloth hardness was 130 HBW?2.5/187.5?.The coefficient of thermal expansion is 6.023×10^-6K^-1,and the thermal conductivity is 144.75W/?m·K?.The overall performance is excellent.?2?The SiC particles be oxidized at 1100°C for 6 h to form a Si O₂ film with a thickness of about 1.1um on the surface of the particles,which can effectively improve the morphology and chemical properties of the particles,and increase the wetting between the SiC particles and the aluminum matrix.The properties of the SiC_p/6061Al composites are denser,and the fracture strength is 195 MPa,the Brinell hardness is 139 HB,the density is 2.76 g/cm3,and the coefficient of thermal expansion is 6.889×10^-6K^-1.These properties are improved relative to the original SiC particulate reinforced aluminum matrix composites,but the thermal conductivity decreased to 116.96 W/?m·K?.?3?The SiC particles were subjected to acid and ball milling with 10%HF solution.The surface of the particles was clean and roughened.As the milling time prolonged,the particle size gradually decreased,and the sharp corners are blunted,besides the particles become round.The performance of SiC_p/6061Al composites prepared by SiC particles that had been washed with acid-washed balls for 10 h was improved in different degrees compared with the original and oxidized SiC_p/6061Al composites.The measured values of the thermal expansion coefficient are close to those predicted by the Turner model,and the thermal conductivity experimental results are close to those predicted by the H·J model,indicating that the thermal conductivity of the aluminum matrix composites with hybrid particles or multimodal particle size distribution can be accurately predicted by the HJ model with the help of equivalent effective thermal conductivity.?4?The SiC_p/6061Al composites were heat-treated at 570°C for 1 h and then incubated at 175°C for 15 h.A large number of second phases were precipitated from the matrix and dispersed.The mechanical properties of the composites were significantly improved.The heat treatment had a weak effect on the thermal expansion properties of the composites.The change trend was not obvious.The thermal conductivity reached a maximum at the 10 h aging time,which was 33W/m·K higher than that of the untreated state,which was an increase of about26.8%.