Study On The Properties Of MnSi₂/316L Composites Manufactured By Selective Laser Melting

316L stainless steel has been widely applied in military industry,chemical industry,biomedicine,shipbuilding and transportation due to its excellent inter-granular corrosion resistance and high temperature oxidation resistance.However,its low hardness,low strength and other problems limit its further development.In order to improve the mechanical properties of 316L stainless steel,this study takes MnSi₂ powder as reinforcement particles and uses SLM technology to manufacture MnSi₂/316L stainless steel composite material.SLM manufacturing process is explored in order to improve the forming quality,mechanical properties and corrosion resistance of composite material.Based on GA genetic algorithm,multi-objective optimization of SLM forming process parameters was carried out.The main research contents and summaries are as follows:（1）Analysis of temperature field of 316L stainless steel composites manufactured by SLM.Jmatpro software was used to obtain the thermal physical parameters of composite materials varying with temperature,and simulation physical model was established.Relying on ANSYS finite element analysis softeware,the influence of process parameters on thermal cycle curve,molten pool temperature and molten pool size of MnSi₂/316L stainless steel composite was investigated.The results show that the addition of MnSi₂ enhanced particles can reduce the heat loss in the process of heat convection and heat conduction in the molten pool,thus increasing the peak temperature of the molten pool,and enhancing the dynamic characteristics of the molten pool by improving the heat conduction and heat convection effects.With the increase of laser power,the existence time of molten pool increases and the size of molten pool increases.The increase of scanning speed leads to the decrease of the molten pool existence time and size.The change of scanning space has relatively little influence on the temperature and size of molten pool,and the effect of adjusting the size of molten pool is relatively weak.（2）Effect of process parameters on manufacturing quality of MnSi₂/316L stainless steel composites.The uniformly dispersed composite particles were obtained by ball milling process,and then the effects of different MnSi₂ addition amount on the surface quality,micro-hardness,tensile properties and corrosion resistance of 316L composite material were investigated.The results show that the addition of MnSi₂ particles leads to the formation of replacement solid solution,which can refine grain.The optimum MnSi₂ ratio is 2 wt.%.Under this ratio,the molten channel of MnSi₂/316L stainless steel composite formed by MnSi₂/316L stainless steel composite is continuous and uniform,the surface defects are few,the equiaxial grains in the microstructure are fine and evenly distributed,the micro-hardness is 326.3 HV_0.2,the tensile strength is 480.5 MPa,and the ductility is 45.27%.It is a typical ductile fracture mode.The corrosion current density and polarization resistance of SMC-2 sample are 1.945μA·cm^-2 and25110.6Ω·cm² respectively.（3）Study on formability of MnSi₂/316L stainless steel composites by adjusting process parameters.On the basis of the MnSi₂ addition selected in the above chapter,a single factor experiment was designed to reveal the influence of various process parameters on the formability of MnSi₂/316L stainless steel composites from the three perspectives of surface density,mechanical properties and corrosion resistance.In the aspect of corrosion resistance,the occurrence of corrosion was further studied according to the sample surface density.The results indicate that the process window is preliminarily determined as follows:160-220 W of laser power,600-1000 mm/s of scanning speed,60-100μm of scanning interval.The corrosion form is pitting corrosion induced by chloride ion.The pitting corrosion mainly occurs at the pore boundary.（4）Optimization of process parameters of MnSi₂/316L composites fabricated by SLM.A response surface experiment scheme was designed.Micro-hardness,tensile strength and corrosion current density were used as response indexes of mechanical properties and corrosion resistance.The forming quality of SLM composites was comprehensively evaluated,and a second-order forming quality prediction model was established.On account of GA algorithm,a multi-objective optimization model was established to achieve the Pareto solution set of process parameters for MnSi₂/316L composites.The results indicate that when the laser power is between 180-195 W,the scanning speed is between 800-850 mm/s,and the scanning distance is between 70-80μm,the forming performance is excellent.Finally,the error between the actual response value and the theoretical response value is calculated through experiments to prove the reliability of the model.