Research On CMT Arc Additive Forming Process And Microstructure And Properties Of Stainless Steel Complex Structure

Wire Arc Additive Manufacturing(WAAM)is a type of wire additive manufacturing technology,because it uses welding arc as a heat source,has high heat input efficiency,high forming efficiency,and can be used for high-efficiency and lowcost forming of larger structural metals.Therefore,it is an important research field in the direction of metal material 3D printing.The basic principle of Arc Additive Manufacturing is to obtain the desired solid structure through the layer-by-layer melting accumulation of the welding wire.In this project,the arc additive technology of cold metal transfer(CMT)is used,and 304 stainless steel is used as the substrate material to study the welding line energy,welding bead angle and interlayer overlap rate encountered by arc additive in the manufacture of complex structures.The effects of other process parameters on its macroscopic molding,microstructure and mechanical properties.The main conclusions are as follows:In the arc additive single-layer single-pass structure,as the wire feeding speed increases,the single-layer single-pass weld width also increases,while the weld bead height first increases and then decreases;as the welding speed increases,the singlelayer single-pass weld bead height and weld width are reduced accordingly.In the arc additive manufacturing structure,the bottom is the fusion zone formed by the first layer of weld bead and the substrate.There is an obvious remelting layer between the layers.With the increase of the welding line energy,the columnar crystals in the arc additive components grow more neatly,the intergranular distance increases,and the secondary dendrites of the columnar crystals grow more continuously and obviously with the increase of the line energy.As the overlap ratio between layers decreases,that is,the inclination of the component increases,the vertical upward growth of the columnar crystals is restricted and forced to tilt,which eventually makes the columnar crystals less continuous,short and easily broken.With the increase of the included angle of the weld bead,the growth restriction of the columnar crystals in the angle region decreases,so the growth space of the columnar crystals increases,the continuity is stronger,and the intergranular distance increases.The hardness of the arc additive straight wall/curved structure gradually decreases along the height direction,from about 210 HV to about 150 HV,a decrease of about28.5%,and finally fluctuates around 150 HV.As the line energy increases,the microhardness of the arc additive structure decreases.The angle of the weld bead and the overlap ratio between the layers have little effect on it,but it will make the hardness change between layers fluctuate more.The tensile strength of the arc additive manufacturing structure is generally greater than the standard tensile strength of the same material by 40～90MPa,which is about7%～17%.However,its elongation is generally less than the standard 5～10%.In the test,when the welding line energy increases by 150J/cm,the tensile strength increases by about 7.3%.