Study On Microstructure And Properties Of Periodic Porous Structure Formed By Selective Laser Melting

Porous materials are increasingly valued and applied due to their dual properties of structure and function.With excellent properties such as light weight,high specific strength,energy absorption and shock absorption,electromagnetic shielding,etc.,cellular materials are widely used in aerospace,medical equipment,weaponry and automobiles molds,architectural art and other fields.Selective Laser Melting?SLM?can quickly prepare complex structural parts that cannot be prepared by traditional processing methods,such as periodic porous heterogeneous density structure,rhombohedron porous structure,etc.and has the advantages of strong forming ability,precise control and high production efficiency.In this paper,SLM technology was used to prepare periodic porous AlSi10Mg alloy with a porosity of 54%,17-4PH stainless steel alloy and high-temperature nickel-based Inconel718alloy,and the effect of heat treatment on its microstructure and mechanical properties was studied.The results are as follows:?1?The microstructure evolution and mechanical properties of the SLM formed porous AlSi10Mg alloy after heat treatment were obtained.The results showed that the structure of SLM formed AlSi10Mg alloy is continuous network eutectic silicon.The microhardness of the cross section is 121.9 HV,and the the longitudinal section is 94 HV.The static compression test results show that the elastic modulus and yield strength of SLM formed AlSi10Mg alloy is 2.032 GPa and 37.31 MPa,respectively.In addition,The plasticity of this porous structure is poor,and the pillars connected to the central node are broken.After AlSi10Mg alloy was heat-treated at 520?×2 h?AC?+160?×6 h?AC?,the silicon particles in the alloy is irregular.Compared with the as-built sample,the hardness values of the horizontal and vertical sections were reduced by 52%and 37%,respectively.The elastic modulus?0.34 GPa?and the yield strength?7.97 MPa?are reduced by 83%and 79%,respectively,because in the solution solution stage,the Si particles that play the role of solution strengthening are precipitated from the matrix and formed the irregular silicon particles,and the solid solution strengthening effect is weakened.During the aging stage,the Si particles grow further,the structure becomes coarse,and the strength of the alloy decrease.?2?The changes of microstructure and mechanical properties of SLM formed 17-4pH stainless steel alloy after heat treatment were revealed.The results show that:the structure of the SLM formed 17-4pH stainless steel alloy contains a large amount of martensite and a small amount of austenite,and the hardness of the cross section and the longitudinal section is different by 5%.Static compression show that the elastic modulus and yield strength of the porous structure are 3.53 Gpa and 116.72 Mpa,respectively.After heat treatment at1040?×2 h?AC?+480?×4 h?AC?,there are martensite and a small amount of residual austenite in the alloy,and the second phase,such as M₇C₃,?-Cu and NbC,existed.The hardness of the cross section is increased by 142%,and the longitudinal section is increased by 51.7%.After compression,the yield strength and elastic modulus are increased by 21%and 35%compared to as-built sample.This is beause the dispersed distribution of?-Cu and NbC are precipitated in the matrix structure during the heat treatment process,which produce precipitation strengthening.These strengthening phases will pin the dislocation,hinder the movement of the dislocation,and increase the strength of the alloy.?3?The changes of microstructure and mechanical properties of SLM formed Inconel718 alloy after heat treatment were obtained.The results show that the SLM formed IN718 alloy contains a large amount of white precipitate phase-Laves phase;the hardness of the cross section is 5.9%higher than that of the longitudinal section.After static compression,the porous structure has a yield strength of 133.49 MPa and an elastic modulus of 4.63 GPa.After 980?×1 h?AC?+720?×8 h?FC,50?/h?+620?×8 h?AC?standardized heat treatment,the alloy contains several phases,including??phase,??phase,?phase and a small amount Laves phase.??phase is distributed in the grain boundary and within the crystal,and?phase is distributed in the grain boundary.Compared with the as-built sample,the hardness of the cross and longitudinal sections is increased by75%and 77%respectively.After compression,the strength and elastic modulus are increased by 46%and 27%,respectively,and the toughness is reduced.The reason of this change is that the??and??strengthening phases are uniformly precipitated in the matrix during the heat preservation process,and the dislocation slippage is hindered by the strengthening phase,then the strength of the alloy increase and plasticity decrease.