| Selective Laser Melting technology is one of the most popular near net shape forming methods in recent years.This method can directly use metal powder to form parts,and the material utilization rate is very high.It is also suitable for parts with complex cavity.In this paper,Ti6Al4V(TC4)powder was used as the experimental material,the process parameters and mechanical properties of TC4 alloy formed by Selective Laser Melting were studied,the effects of process parameters and heat treatment process on the density,microstructure and mechanical properties of SLM formed TC4 titanium alloy were also discussed.the research content and main conclusions of this paper are as follows:The effects of main process parameters(laser power,scanning speed,scanning distance and powder thickness)on the forming quality,microstructure and mechanical properties of SLM formed TC4 alloy samples were studied to determine the optimum process parameters of SLM forming TC4 alloy samples.They were as follows:laser power 400 W,scanning speed interval 1800mm/s~2200mm/s,scanning spacing 0.07 mm,and powder thickness 0.05 mm.The density of SLM formed TC4 alloy sample was up to 99.5% within the range of the process forming region.The results show that the surface micromorphology and mechanical properties of the specimen present a tendency to get better first then turn bad with the increase of the process parameters.Under the optimized process parameters,the effects of different energy densities on density and microstructure of SLM formed TC4 alloy specimens in different placement directions were studied,and their mechanical properties were studied at room temperature tensile test.The results showed that when the energy density was 57J/mm3,the tensile strength and yield strength of x direction SLM forming TC4 alloy reached the maximum,respectively 1210 MPa,1128MPa,the elongation rate was 2.16%;while the y direction on the tensile strength and yield strength were 1190 MPa and 1107 MPa,the extension rate was 2.05%.With the increase of the energy density,the defects of spheroidization and over melting were easy to appear in the alloy sample,which reduces the properties of the alloy sample.By changing the parameters,discussed the relationship between the sample properties of SLM formed TC4 alloy under the condition of the same energy density(50J/mm)It was found that the quality and performance of the sample were quite different because of the different combination of the process parameters while under the same energy density.The effects of different heat treatment processes on the microstructure,phase distribution and mechanical properties of SLM formed TC4 alloy samples were also studied.The study found that when SLM forming TC4 alloy under 2h annealing temperature of 800℃,850℃and 900℃,the martensite ɑ’ phase were decomposed,as the annealing temperature gradient increased,the microstructure in alpha’ phase decomposed into strip with width decreased.At 800℃/2h after annealing,part of martensite discomposed into fine and dispersed(ɑ +β)phase,improving TC4 titanium alloy hardness and strength.With the increase of annealing temperature,the hardness and strength of the alloy samples decreased gradually,but the elongation of the sample was improved.After annealing treatment,the residual stress of TC4 alloy specimen was gradually increasing,and the residual stress was the lowest at 800℃/2h annealing condition,and its value was 43 MPa.SLM forming TC4 alloy after solid solution and aging heat treatment did not appear the equiaxied alpha phase,with the solid solution temperature increasing,alpha phase width gradually increased,the strength and hardness of the alloy increased first and then decreased,and a certain strengthening effect was achieved.The tensile strength and yield strength of the alloy specimens reached the maximum value of 1314 MPa and 1221 MPa under the condition of 960℃/1h+560℃/4h solid solution and aging stage,and the elongation was 2.3%.Comparing the microstructure and room temperature tensile properties of the samples under different heat treatment,it was known that the annealing process at 800℃/2h furnace was the best heat treatment process,and the tensile strength of the formed samples could reach 1349 MPa and the elongation could reach 2.5%.Through the study on the process and properties of SLM forming TC4 alloy in this paper,TC4 alloy samples with high quality and high performance was successfully prepared and the influence of process parameters and heat treatment process on the microstructure and mechanical properties of SLM formed TC4 alloy samples was revealed.It provided a certain technical basis and theoretical basis for the application of TC4 alloy powder in the industrial application of laser melting rapid prototyping. |
