Effect Of Mg And Si Content On Microstructure And Mechanical Properties Of Al-Mg-Si Alloy Fabricated By SLM

Al-Mg-Si alloy is widely used in automotive,aerospace,and other fields because of its good processability,high specific strength,and high corrosion resistance.However,it faces the challenge of hot crack in the processing by selective laser melting（SLM）.This work reduces the hot crack sensitivity of Al-Mg-Si alloy through composition design,carries out low-temperature aging,and explores the microstructure and mechanical properties of SLM fabricated Al-Mg-Si alloy.The following conclusions are drawn:（1）With the increase of volumetric energy density（50～130 J/mm³）,the relative density increases first and then decreases.The optimized process parameters are as follows:250 W of power,1000 mm/s of scanning speed,40μm of hatch spacing,getting a low crack density of5.96×10^-3μm/μm².The printed 6063 aluminum alloy（AA6063）is a supersaturated solid solution.After aging at 160℃/4h,the ultimate tensile strength,yield strength,and elongation are 241 MPa,120 MPa,and 4%respectively.The properties are higher than those of casting and forging.The anisotropy of crack propagation causes the strength and ductility of the vertical plane to be higher than that of the horizontal plane.（2）Adding 1.7 wt%Si increases the hot crack tendency of AA6063,and the crack density is 26.13×10^-3μm/μm²,crack initiation along large angle grain boundary.Excess Si is enriched at the boundary of molten pool and grain boundary,resulting in grain boundary brittleness and grain coarsening.The scanning strategy of checkerboard+strip improves the mechanical properties of the sample,and the peak strength is 57 MPa.（3）The microstructure of Al-4.4Mg-3.1Si alloy fabricated by SLM is dense,the relative density is 99.4%,and there is no crack.The alloy has columnar crystal morphology,fine grain,and high-strength mechanical properties.The ultimate tensile strength is 452 MPa,the yield strength is 421 MPa,and the elongation is 3.2%.Aging treatment promotes the precipitation of Mg₂Si phase in Al matrix,and the precipitated phase changes from printed short rod to spherical,accompanied by the coarsening of Si particles.After aging at 300℃/4h,the ultimate tensile strength is reduced to 211 MPa,the yield strength is154 MPa,and the elongation is increased to 11.5%.After aging,the effects of solid solution strengthening,dislocation strengthening,and dispersion strengthening are reduced,which reduces the strength and improves the ductility.