Simulation On Temperature And Stress Field And Experimental Investigation Of Magnesium Alloy By Selective Laser Melting

In this paper,we use finite element analysis software ANSYS,APDL command flow language to carry on the loading of moving gauss heat source and the application of birth and death element.Firstly,the effects of scanning velocity,laser power and whether the substrate preheating or not on the forming temperature field of magnesium alloy by Selective Laser Melting(SLM)were studied.Through the simulation of the temperature field,we find: in the process of SLM forming,the temperature field of molten pool is a typical ellipsoid,the maximum temperature and the size of molten pool is affected by the laser power and the scanning velocity,which increases with the increase of laser power,and decreases with increase of scanning velocity.Substrate preheating can greatly improve the temperature field distribution,improving the temperature of the powder and the substrate,and then reduce the temperature gradient.Based on the numerical simulation of temperature field,the influence of scanning velocity,laser power and whether the substrate preheating or not on the stress field and residual stress of magnesium alloy was studied by finite element thermos-structural indirect coupling method.The result indicates that: in the region of laser forming during the selective laser melting,the melting materials are higher than that of the melted area due to the thermal expansion and contraction.And when the laser leaves,the melted region will contract to form a depression during the liquid metal cooling for solid.In the forming region the material is in the state of tensile stress,the subsequent scanning causes the tensile stress to be released to a certain extent.The stress concentration generally occurs at the position where the powder is combined with the substrate and reaches the maximum at the beginning of the scanning position,which is the same as the position of the warpage and delamination in the experiment.The residual stress of the forming parts is proportional to the scanning velocity and is inversely proportional to the laser power,in other words,the residual stress in the forming parts increases with the increase of scanning velocity and decreases with the increase of laser power.The thermal stress and residual stress in the process of forming the magnesium alloy by SLM are correspondingly decreased since the preheating of the substrate changes the temperature field distribution and reduces the temperature gradient.The experimental results show that the density of the magnesium alloy sample is more than 96% under the conditions of laser power of 200 W,scanning velocity of 300mm/s and substrate preheating temperature of 80℃,the microstructure is in a typical honeycomb with a more uniform distribution and finer grain size,and the particle size is between 3~7μm.Subsequently,under this process parameter,magnesium alloy skeleton part is formed,which indicates the feasibility of using SLM to form magnesium alloy parts.Finally,residual stress of specimens of magnesium alloy were measured using the micro-indentation method.It is found that the residual stress increases with the increase of the scanning velocity and decreases with the increase of the laser power,which is consistent with the trend of the numerical simulation.It shows that the numerical simulation is able to predict the residual stress in the SLM forming products to a certain extent.