Microstructure And Mechanical Properties Of SiC/Al Composites Casting By Low Pressure Cast

In this paper,the microstructure and mechanical properties of SiC/Al composites under low pressure casting are studied,and the effects of process conditions on melt casting properties and compactness of castings are investigated.The effects of holding pressure and pouring temperature on the microstructure and properties of the composites were investigated by cross-contrast.The castings were subjected to T6 heat treatment to study the effect of wall thickness on the properties after heat treatment.At a higher holding pressure(70kPa),the agglomeration of SiC particles has a slight decrease,the distribution of SiC particles is more uniform,and the composite has less tissue impurities.The dimensional uniformity and size of the grains under the two pressures are not much different.The effect of holding pressure on melt flowability and compactness is not obvious,but the hardness,tensile strength and elastic modulus values are significantly improved at higher pressures.At higher casting temperatures(710°C),the agglomeration of SiC particles has a slight increase,the distribution of SiC particles is more uneven,and the composites have more tissue impurities.The uniformity of grain size at the two temperatures is not much different,but at higher temperatures,the grain size is larger.Increasing the pouring temperature can significantly improve the fluidity and compactness of the melt,but the hardness of the structure does not change significantly.At higher casting temperatures,the tensile strength of the three wall thickness plates increased by 23.3%,increased by 10.7% and decreased by 69%,and the elastic modulus of the composite decreased,with an average decrease of 5.6%.The size of the crystal grains increases with the increase of the wall thickness.After the heat treatment,the density of the different thickness of the plate is 10 mm larger than 20 mm,and 20 mm is larger than 15 mm.Under the conditions of 60 kPa,690 °C and 70 kPa,710 °C,the hardness,tensile strength and elastic modulus of the 15 mm wall thickness are the highest.Under the condition of 70 kPa and 690°C,the 15 mm wall thickness plate has the lowest performance value,while the 10 mm wall thickness plate is the largest.The heat treatment can increase the tensile strength and hardness of the material.The tensile fracture mode before and after the heat treatment is brittle fracture,and the crack source is at the interface junction between the reinforcement and the matrix.