Study Of Microstructure And Properties Of Al AlSi10Mg Prepared By Slm And Its Residual Stress By Numerical Simulations

Selective Laser Melting(SLM)technology is widely used in the additive manufacturing of aluminum alloy materials due to its characteristics such as fast forming speed and good performance of formed parts.However,there are a lot of residual stresses inside the AlSi10 Mg formed by SLM,which leads to cracking and deformation of the formed parts.In this study,Simufact additive 4.0 finite element simulation software was used to simulate the prnting process of AlSi10 Mg workpieces printed by SLM to explore the temperature field distribution inside the part during the printing process,the influence of the printing parameters on the residual stress inside the part and the joint surface of the part and the substrate.Analyze the main factors affecting the residual stress through the orthogonal test.Perform stress relief annealing and artificial aging treatment on the printed parts,and research the effect of heat treatment on the residual stress,microstructure and mechanical properties of the printed parts.Through numerical simulation found that due to the influence of high-energy laser beam and heat conduction,each printing layer has three peak temperatures,and the difference between the three peak temperatures is large.A large temperature gradient is formed during the cooling and solidification process,resulting in greater internal stress.Through variable parameter simulation calculations and experiments,it was found that with the increase of substrate temperature,laser power,scanning speed and scanning distance,the residual stress inside the workpiece and the bonding surface first decreased and then increased.The substrate temperature has a significant effect on the residual stress of the thin-walled structure,and the laser power,scanning speed and scanning interval have a more significant effect on the residual stress of the thick-walled structure.The laser power is too low or the scanning speed and scanning distance are too high,it is easy to cause internal defects in the part to increase,affecting the forming quality of the printed part.Through orthogonal experiments,it was found that the most important parameters that affect the residual stress inside the print and the bonding surface are the scanning speed and the scanning interval respectively.The optimal parameter combination is laser power 450 W,scanning speed1100mm/s,scanning interval 70?m,substrate temperature 180?.Through microstructure observation and mechanical property test,it was found that the cooling speed of SLM prints is fast,the supersaturated Si atoms exist in the Al matrix,the Si phase is distributed in a network,the structure is fine and dense,and the microstructure shows three regions of coarse crystal area,fine crystal area,and heat-affected area.The tensile strength,yield strength and elongation of the parts reached 480 MPa,310MPa and 6% under solution strengthening and fine grain strengthening respectively.After annealing treatment,the structure of the coarse crystal region in the microstructure changes from an irregular shape to a long interwoven structure growing in a certain direction under the internal stress.The overall residual stress is reduced by 27.7%-32.3%;the solid solution strengthening and fine grain strengthening are weakened,and the strength and hardness of the parts are reduced.After aging treatment at 180 ?,the research found that: During the heat treatment,the Si phase will gradually precipitate out of the matrix,and the solid solution strengthening effect weakens.After 6 hours of aging treatment,the tensile strength,yield strength and elongation of the parts were 358 MPa,220 MPa and 4.85%,respectively,which reduces the performance gap between the parts and the T6 treated castings.Therefore,using the substrate after solution treatment,heating the substrate printing can effectively reduce the generation of stress and improve the binding rate.