Effect Of Substrate Temperature And Heat Treatment On Microstructure And Properties Of Al-Mg-Sc Alloy Plate Manufactured By Selective Laser Melting

Laser selective melting（SLM）has been widely used in the manufacture of complex metal components with high precision due to its high precision,excellent surface quality and no subsequent processing.In the process of preparing SLM,the instantaneous energy of laser is very high,and the temperature gradient difference is large when the molten pool solidifies,which may cause the thermal stress and residual stress in the printing alloy,causes the alloy to have the periodic crack or can not print the forming the question.By increasing the temperature of the substrate and preheating the substrate and powder before printing,the distribution of the temperature field can be improved and the formability of the printed member can be improved.But when the substrate temperature is high,the difference of temperature gradient from the bottom to the top of the substrate may cause the difference of microstructure and properties of the alloy components along the printing height direction.In particular,when a part is printed with a higher height or with a more complex structure,with the extension of the printing time,the heat effects and the length of time from the bottom to the top of the alloy member are different,as a result,the microstructure and mechanical properties of the alloy show inhomogeneity to some extent.Therefore,the Al-3.40Mg-1.08Sc alloy sheets prepared by SLM technique are taken as the research object,and the high strength aluminum alloy sheets are prepared at substrate temperature of 35°C and 200°C,respectively.The microstructure,mechanical properties and corrosion resistance of the alloy plates prepared at different substrate temperatures along the printing height direction were compared,the influence of substrate temperature on the nonuniformity of the structure and properties of the printed sheet along the printing height direction is revealed.Through the post-treatment process of heat treatment,the evolution rules of microstructure,mechanical properties and corrosion properties of the heat-treated alloy sheet from bottom to top are revealed,the uniformity of microstructure and properties of heat-treated alloy sheet along the printing height direction was investigated.It is expected to provide theoretical and experimental support for the preparation of Al-Mg-Sc alloy components with certain height by SLM.The main conclusions are as follows:When the substrate temperature is 35°C,the grain structure of Al-3.40Mg-1.08Sc alloy plate is uniform from the bottom to the top,which is the appearance of fine equiaxed grain and narrow columnar grain.When the substrate temperature is raised to 200°C,the temperature gradient produced by the substrate decreases from top to bottom,the grain size and distribution area of equiaxed grains in the alloy increase,and the aspect ratio and distribution area of columnar grains decrease,the number of the second phase in the bottom of the alloy plate increases obviously because of the heat effect of the substrate for a long time.The hardness distribution and tensile properties of the alloy sheet prepared at 35°C are basically the same along the printing height direction.However,the alloy plate prepared at 200°C has a certain aging effect because of the heat source near the bottom and middle of the plate,which is affected by the heat for a long time,the hardness and tensile properties of the alloy sheet prepared at 35°C were significantly higher than those of the alloy sheet prepared at 35°C:The hardness of the bottom is about 20HV higher than that of the top,and the tensile strength and yield strength of the bottom are about 50MPa higher than that of the top.Because the Cu-rich phase near the grain boundaries of Al-3.40Mg-1.08Sc alloy has higher electrochemical potential than the aluminum matrix,the surrounding matrix is preferentially dissolved,so the bottom of the molten pool with higher grain boundary density is the most severely corroded.At the substrate temperature of 35°C,the Cu and Mg in the alloy are continuously distributed along the grain boundary.While at the substrate temperature of 200°C,the cooling rate of the plate along the printing height direction increases gradually,and the size of Cu-rich phase near the grain boundary at the bottom is large and its distribution is discontinuous,the growth of intergranular corrosion channel is hindered.Therefore,the corrosion resistance of the alloy sheet prepared at 200°C is improved from top to bottom,and it is better than the alloy sheet prepared at 35°C.After Peak ageing treatment at 300°C/12h,no matter the substrate temperature is35°C or 200°C,the mechanical properties and corrosion properties of the alloy plate from bottom to top are basically the same,and they are obviously better than the initial state.Compared with the initial state,the improvement of the mechanical properties of the Al-3.40Mg-1.08Sc alloy sheet is mainly caused by the precipitation of Al₃（Sc,Zr）particles,and the improvement of the corrosion resistance is mainly due to the increase of the grain size,resulting in The corrosion resistance of the alloy sheet after aging is increased.