Research On Welding Characteristics Of Typical Materials Manufactured By Selective Laser Melting

The combination of selective laser melting(SLM)and welding technology provides a new way to build large and complex 3D-printing parts,which is expected to improve the yield and forming efficiency with low cost and has a wide potential for further applications.However,since the SLM components are very different in microstructure and properties from those manufactured by conventional processes of casting and forging,whether the SLM components have good weldability and the influence of SLM characteristics on welding process are unknown.Therefore,welding characteristics of three typical materials such as 304 stainless steel,GH4169 alloy and Ti6Al4 V alloy manufactured by SLM were studied in this thesis.The main conclusions are as follows:Firstly,the weld qualities of laser welding and laser-arc hybrid welding are evaluated.Laser welding joints reach B-class standards and the hybrid welding joints reach A-class standards,respectively.Secondly,the microstructure of welds and the influence of the anisotropy and defect in the SLMed base metal are discussed.The microstructure of welds belongs to typical molten pool solidification structure.Fine cell crystals grow epitaxially from base metal at the fusion line,and the microstructure at the edge is composed by the hybrid columnar crystal of cell and dendrite.Different microstructures are obtained in the weld center caused by different materials and processes.For 304 stainless steel and Ti6Al4 V alloy,the microstructure in the center of weld is the vertical columnar crystal,and for GH4169 alloy is equiaxed dendrites or equiaxed crystal.Anisotropy has an influence on the weld structure by affecting the welding heat process.When the welding direction is the same as the building direction of SLM process,the welds with uniform width and fine grains can be obtained.Finally,the mechanical and corrosion properties of welded joints are studied.The tensile properties of 304 stainless steel and GH4169 alloy welded joints reveal a drop trend compared with the SLMed base metals.The maximum tensile strength of the 304 stainless steel joints is 94% of that of the base metal and is close to that of the conventional forgings.The maximum tensile strength of the GH4169 alloy joints is 94.4% of the base metal.Ti6Al4 V alloy joints get higher tensile strength than the base metal.Microhardnesses of welds with different materials show a good match with those of tensile properties.Anisotropy has an obvious effect on the mechanical properties.When the welding direction is the same as the SLM building direction,the mechanical properties are the best.All welds exhibit stronger corrosion resistance than the SLMed base metals.The reason may be that a small amount of pores in the SLMed base metals can increase the actual corrosion area and easily become a pitting source to reduce the stability of the passivation film.The effect of anisotropy on corrosion performances is not obvious.