Study On Microstructure And Properties Of AlSi7Mg And Modified Materials Prepared By Selective Laser Melting

Aluminum alloys are essential structural materials because of their lightweight,high specific strength and specific stiffness,good electrical and thermal conductivity.It is difficult to optimize the shape and performance of complex aluminum alloy components by traditional forming methods.Selective Laser Melting(SLM)provides a new way for the integrated forming of high performance aluminum alloy complex components.However,the problems of crack,pore and high residual stress in forming of traditional high strength aluminum alloy make it difficult to fabricate by SLM.In this paper,based on AlSi7Mg in the traditional hypo eutectic Al-Si alloy,the regulation of SLM process parameters and annealing heat treatment on the microstructure and properties of AlSi7Mg was studied;a new type of high strength,high strain and high wear resistance composite material modified by nano-Si C particles,and a new type of high strength and high strain alloy modified by rare earth Sc were designed and prepared;the evolution of microstructure and the strengthening mechanism of mechanical properties of the new modified alloys were revealed;and taking the complex lattice structure of AlSi7Mg/nano-SiCp composites formed by SLM as an example,the research on shape optimization and control of complex components with high performance was carried out.The main conclusions are as follows:The effects of process parameters(laser power,scanning speed)on the density,microstructure,phase composition and mechanical properties of AlSi7Mg were studied.The residual stress was reduced by 87.6%after annealing heat treatment.At the same time,the tensile strength and elongation of the annealed sample reached to 226.32±3.06 MPa and12.87±1.68%,respectively,which were higher than those of traditional casted AlSi7Mg.AlSi7Mg/nano-SiCp composite powder was prepared by mechanical ball milling to improve the laser absorption rate of aluminum alloy powder.The high strength and high strain composite was fabricated by SLM,whose tensile strength and elongation reached to 502.94±6.4 MPa and 10.64±1.06%,respectively.Although the corrosion rate of the composite was higher,the inert phase nano-Al₄C₃ generated by the in-situ reaction and a small amount of residual nano-SiCp can block the matrix connectivity and make the pits difficult to expand and deepen.Based on Scheil solidification model,Sc modified AlSi7Mg alloy was designed,and AlSi7Mg-x Sc modified alloy powder was prepared by gas atomization method.The reaction of oxygen philic Sc elements with oxygen atoms to produce Sc₂O₃ can realize the deoxidation of molten pool.The in-situ reaction phase AlSc₂Si₂ had a semi-coherent relationship with Al matrix,and the synergistic effect of Al₂O₃ and Sc₂O₃ at the molten pool boundaries refined the grain,making the tensile strength and elongation reach to 411.05±4.21 MPa and 9.45±0.86%,respectively.Due to the lower thermal conductivity and higher melting point of the composite material,the degree of sticky powder in preparation of lattice structures during SLM process was improved.Therefore,compared with the BCC lattice structure of AlSi7Mg formed by SLM,the forming accuracy and compressive properties of the lattice structures of AlSi7Mg/nano-SiCp were improved.The research results of this paper provided new materials and theoretical basis for the engineering application of aluminum alloy fabricated by SLM.