Effects Of Solution Treatment On Microstructure And Mechanical Properties Of SiC_p/2024Al Composites Fabricated By Powder Thixoforming

SiC_p/2024Al composite have been fabricated by powder thixoforming,and the effects of solution treatment on the microstructure and mechanical properties have been investigated.As comparing,the solution treatments of the powder-thixoformed 2024 Al alloy and the permanent mold cast alloy also were studied.The results indicated that the microstructure of powder-thixoformed SiC_p/2024Al composites is composed of primary α-Al,neted secondary solidified structures(secondary primary α-Al and eutectic structures)and SiC particles which distribute in the secondary solidified structures.Due to the presence of SiC particles,the strength of powder-thixoformed composites is higher than that of powder-thixoformed matrix alloy.The ultimate tensile strength and yield strength increased from 300 MPa and220MPa(for the matrix alloy)to 330 MPa and 240MPa(for the as-fabricated composite),respectively,but the elongation decreased from 12% to 4.7%.The microstructural evolution of powder-thixoformed SiC_p/2024Al composite includes two stages during solution treatment,the first stage(0-4h)involves the rapid growth of primary α-Al grains and secondary primary α-Al grains,and eutectic phase quickly dissolutionized.The second stage(4h-24h)involves normally slow growth.However,microstructure of powder-thixoformed 2024 alloy has completed the quick dissolution of the eutectic phase from 0 h to 1.5 h(the first stage).Due to the presence of large interdendritic eutectic phase during solutionizing at 485 ℃,the microstructural evolution rate of the permanent mold cast alloy is slower than that of the power thixoformed alloy,needed 4 h(the first stage)to complete the quick dissolution of the eutectic phase.The mechanical properties of powder-thixoformed SiC_p/2024Al composites solutionized at 485℃ for 7 h reached the peak values,with the ultimate tensile strength,yield strength and elongation of 362 MPa,300 MPa and 8.6%,and were increased by 9.7%,25%,and 82.9%,respetively,as compared to the powder-fabricated composite.However,the mechanical properties of powder-thixoformed 2024 alloy reached peak values at 485℃ solutionization for 4 h,the ultimate tensile strength,yield strength and elongation were increased from300 MPa,220MPa and 12% to 333 MPa,278MPa and 16.5%,respectively.The mechanical properties of permanent mold cast alloy reached peak values at 485 ℃solutionization for 10 h,the ultimate tensile strength,yield strength and elongationwere 320 MPa,264MPa and 7.2%,respectively,and were increased by 26.5%,45.1%and 132.3%,respectively,as compared to the solution before.The strengthening mechanisms of composites include direct strengthening and indirect strengthening,in this work,combined this two strengthening mechanisms,and used the modified MSL model considering particle failure to predict the yield strength of the SiC_p/2024Al composites after solution treatment.The theorical calculated value is close to the experimental value,and between of them have the similar variational tend.