Study On The Wire And Arc Additive Manufacturing Technology Of 5356 Aluminum Alloy Under Cooling Constraints

Wire and Arc Additive Manufacture(WAAM)has the advantages of short manufacturing cycle,high deposition efficiency,high wire utilization and low cost.It was especially suitable for productions of large size and complex components with small batch and low cost.However,the poor arc stability and large heat input make the molten pool flow easily,which affects the forming accuracy of the parts.The serious heat accumulation leads to the uneven microstructure and mechanical properties of the formed parts,and the long cooling time between layers reduces the deposition efficiency.The repeated thermal cycle might easily cause the surface oxidation of the aluminum alloy formed parts.In this paper,5356 aluminum alloy was manufactured by double pulse arc additive manufacturing to study the forming process and microstructure of the forming parts.In the process of the WAAM,the cooling fixture which was self-designed was applied on both sides of the molten pool.The microstructure and performance of the aluminum alloy thin-wall parts formed by WAAM in cooling constraints were explored and analyzed.Firstly,the optimal process of double-pulse arc additive manufacturing of aluminum alloy was explored through a series of single-layer welding tests.The weld bead was well formed with welding current I= 130 A,arc voltage U = 20 V,welding speed v= 7mm/s and frequency f=4Hz.The 5356 aluminum alloy vertical-wall part was fabricated according to these parameters.The verticalwall part was well-formed,the side of wall was rough,the average layer height was about 1.6mm,and the cooling time between layers was 10 min.The inclined wall part can be formed with an angle of 45° when the angle of welding torch was 15°and the transverse displacement was 1 mm.When the fixture gap was8 mm,the side surface of the vertical-wall part fabricated with the same parameters was flat,the average layer height was about 3.1mm,and the forming quality and deposition efficiency were improved.The results showed that the grains on the surface and between the layers of the specimens were fine,columnar crystal and coarse equiaxed crystal distributed in the layer.The grains of vertical wall showed alternate distribution of equiaxed and columnar grains in the height direction,and the hardness changed periodically.The grains of the vertical-wall parts fabricated under cooling constraints were refined and the growth of columnar grains was restrained.The average hardness of the vertical-wall part without cooling was 77 HV,and the average hardness of the vertical-wall part with cooling increased to 85 HV.After aging treatment at 450 ? for 4 hours,the number of dispersed black particles decreased significantly,and the average hardness increased to 90 HV.The tensile properties of 5356 aluminum alloy vertical wall were anisotropic.The ultimate tensile strength in x-axis direction was about 6% larger than that in z-axis direction.The effect of cooling constraints on the tensile properties of 5356 aluminum alloy vertical-wall was small.It can be observed through EDS analysis that Mg and Si have obvious segregation in grains.