Froming Process,Microstructure And Properties Of Selective Laser Melted Al-Mn-Mg-Sc-Zr Alloy

In recent years,the selective laser melting forming technology has made great contributions to the rapid development of modern industry.The forming characteristics of near net forming and rapid cooling provide a new way and method for the preparation of high-strength aluminum alloy complex structure parts.However,the influence of process parameters on cracks in the forming process of Al-Mn-Mg-Sc-Zr alloy by selective laser melting forming is not clear.The precipitation rules of Mn and Sc elements in complex thermal cycle and heat treatment process need to be clarified.In view of the above problems,Al-Mn-Mg-Sc-Zr alloy was formed by selective laser melting technology in this paper,and the influence of laser power and energy density on crack generation was mainly studied.The influence of heat treatment on the microstructure and properties of materials was explored.This study provides experience and guidance for selective laser melting forming of high strength aluminum alloy complex parts.The main research results are as follows.(1)By optimizing the process parameters of selective laser melting forming,the crack-free Al-Mn-Mg-Sc-Zr forming sample can be prepared by using the process with energy density of 138 J/mm3 and laser power of 370 W.The relative density reaches 99.30%.The ultimate tensile strength of the as-deposited and 300?/5 h aging heat-treated materials prepared by the optimized process at room temperature were 455 MPa and 556 MPa,respectively,and the elongation after fracture were 15.4%and 14.2%,respectively.The strength of the material was increased by 22%,and the elongation after fracture was not significantly reduced.The fracture morphology analysis shows that the fracture of tensile specimen is brittle fracture macroscopically and ductile fracture microscopically.(2)The influence of selective laser melting forming process parameters on the microstructure of the formed sample and the influence law on the crack generation were studied in depth.The increase of energy density and laser power will lead to the increase of porosity and reduce the density of the sample.Reducing the energy density eventually leads to the increase of thermal stress,resulting in cracking.Keeping the energy density constant,reducing the laser power will increase the interaction time between the laser and the powder,reduce the cooling rate,and precipitate coarse Al6Mn phase,which increases the risk of micro-stress concentration and leads to cracking.(3)Through the microstructure analysis of the as-deposited state materials,higher cooling rate can increase the solid solution content of each element in the aluminum matrix to obtain supersaturated solid solution.The primary Al3Sc particles provide more nucleation sites for the solidification process,and good grain refinement effect can be obtained with higher cooling rate.Nano-sized Al3(Sc,Zr)and Al6Mn particles are distributed at the grain boundaries,which inhibit the expansion of grain boundaries and refine grains during solidification.After heat treatment,the grain size was slightly coarsening,and a large number of dispersed nano-sized Al3(Sc,Zr)and Al6Mn particles were precipitated in the grain,which played a good precipitation strengthening effect on the matrix and improved the mechanical properties of the alloy.