Effects Of Solution Treatment On Microstrcture,Mechanical Properties And Strengthening Mechanism Of SiC_p/2024Al Matrix Composites Fabricated By Powder Thixoforming

Al-based composites reinforced with SiC particles were widely used in electricity,aerospace and automobile industries because of the light weight,high specific strength,high specific stiffness,and outstanding wear resistance.Unfortunately,the traditional technology could not produce the SiC_p uniformly distributed composite materials at low cost.Meanwhile,the materials exhibited poor plasticity due to the addition of reinforced SiC_p,which limited their developments and applications.It is well known that heat treatment not only can enhance the strength of composites,but also improve the elongation of composites.In this work,SiC_p/2024Al was fabricated by powder thixoforming?PTF?.Afterwards,the effects of the solution treatment on the microstructure and the mechanical properties of the composites were investigated.The fracture surface,fracture profile and in-situ tensile test of the composites were used to analyze the fracture mechanism of the composites.Finally,a theoretical mo del for calculating the Yield strength of the composite was obtained.In contrast,2024 alloys fabricated by permanent mould cast?PMC?and PTF were studied respectively,The main research results are as follows:The microstructure of the SiC_p/2024Al was composed of spherical or near-spherical primary particles??-Al?,uniformly distributed SiC particles and intergranular secondarily solidified structures.Compared with the 2024 alloy fabricated by PT F(?_b=305MPa??_0.2=207MPa)the ultimate tensile strength??_b=350MPa?and yield strength(?_0.2=245MPa)of the composites were increased by 14.8%and 18.4%.However,the elongation dropped from 11.2%to 4.4%.SiC_p/2024Al matrix composites structure evolution can be divided into two stagesduring solution treatment.The first stage involes rapid dissolution of eutectic?-Al₂Cu and S-Al₂Cu Mg accompanied by coarsening the primary particles.The second stage is the slow dissolution of eutectic and the normal growth of primary particles.Compared with PTF-2024 aluminum alloy,composites material structure evolution rate is slower.The best parameter of solution treatment of composites materials was490?×6h.The peak tensile properties of the composites were ultimate tensile strength of 398Mpa,yield strength of 320Mpa,and elongation of 8.45%,which were increased by13.7%?30.6%?92%respectively compared with fabricated composites prepared by PTF.The best solution parameter of 2024 aluminum alloy was 490?×3h.On this condition,the tensile strength was 350MPa,yield strength was 285MPa,and the elongation was17.5%.Compared with the fabricated 2024 aluminum alloy,they increased by 14.6%,37.7%and 14.6%respectively.After solid solution treatment,compared with matrix alloy,the increase of composite material elongation was more obvious.The fracture of the composites without solution treatment was intergranular fracture.With the temperature of solution reached 475?,the fracture transformed into a mixture regime of transgranular fracture and intergranular fracture.The fracture mode changed again at 505?,it was dominated by transcrystalline fracture.Considering the effect of solution treatment and failure fraction of SiC _p,a strengthening model based on the load transfer mechanisms was obtained,and it indicated a good agreement between the experimental and calculated values of yield strength.