Compound Forming Of 316L Stainless Steel Based On Selective Laser Melting And Laser Welding:Microstructure And Mechanical Properties

Selective laser melting(SLM)is the most representative additive manufacturing technology,which can realize precise forming of complex metal components.However,the defects and dimensional accuracy of large-size SLM forming parts are difficult to control,which limits the application of SLM technology to large-scale parts.In order to break through the limitations of SLM technology and reduce the difficulty of manufacturing large and complex structural parts,the selective laser melting forming technology and welding technology are combined.Under the premise of ensuring the reliability of the structure,it can reduce production costs and improve production efficiency.It has a wide range of applications.prospect.In this thesis,316 L stainless steel is used as the research material.First,the performance difference between SLM formed parts and forging parts is studied,and then the laser welding between SLM forming parts and between SLM forming parts and forging parts is carried out in different directions.Research on joint process,organization and performance.The conclusions are as follows:Through the characterization of the material microstructure,element composition,and phase structure,it is found that under the influence of the forming method,the stacking plane and the scanning plane of the SLM forming part have a completely different microstructure.There is no difference between the element content and the element distribution of SLM formed parts and forged parts,and the phase structure composition is FCC structure austenite structure.Tensile test,hardness test,and electrochemical corrosion test are used to test the material properties.The results show that SLM formed parts have obvious anisotropy.The hardness and tensile strength of SLM formed parts are significantly better than that of forged parts,and the elongation rate of SLM formed parts is worse than that of forged parts.The main reason for the above difference in performance is the large difference in the grain boundary angles in the material.The small-angle grain boundaries in the SLM formed parts have obvious strengthening effect on the strength;while the large-angle grain boundaries in the forged parts are mainly large-angle grain boundaries,which have an impact on the toughness.Great contribution.The corrosion resistance of SLM formed parts is also significantly better than that of forged parts.Under suitable laser welding parameters,SLM formed parts exhibit good welding performance.Research on the structure and properties of welded joints found that compared with SLM forming base materials,laser welded welds exhibited coarser dendrite structure,lower microhardness and tensile properties.The tensile strength of the joint is close to that of the forging,and the elongation is about half of that of the forging.The anisotropy of SLM formed parts has a certain influence on the structure and mechanical properties of laser welded joints.The corrosion resistance of welded joints of SLM formed parts is better,and the welded joints of SLM formed parts and forgings have poor corrosion resistance;the forged parts are the most corroded part of the welded joint;the passive film impedance characteristics of all welded joints the same.In order to improve the plastic toughness of the joint,heat treatment is performed on the welded joint.The results show that the low-temperature annealing treatment can refine the grains in the weld to a certain extent,so that the microhardness can be slightly increased by 10%;the tensile strength of the welded joint can be increased by up to 9.5%,and the elongation rate can be increased by up to 61.9%;The corrosion performance does not change much,and the quality of the passivation film slightly decreases.After solution treatment,the microscopic morphology of the base metal changes greatly,the boundaries of each part of the joint become blurred,and the grains in the weld area grow and merge into large-size grains;the tensile strength of the joint does not change significantly but the plasticity increases by 68.9%?81.9%;The corrosion resistance of the joint is improved,but the quality of the passivation film is significantly reduced.