Temperature Field,Microstructure And Mechanical Properties Of 2219 Aluminum Alloy Manufactured By WAAM

Wire and Arc Additive Manufacturing(WAAM),using arc as heat source and wire as the additive material,fabricate three-dimensional metal parts layer-by-layer which are close to product shape and size requirements under program control.Compared with the metal additive manufacturing technology with the laser and electron beam as the heat source,WAAM has the advantages of high wire utilization,fast deposition speed,low manufacturing cost,and the capability of building large scale components.However,WAAM technology is the continuous build-up welding process in essence,and the problems encountered in welding also exist in the WAAM process.The poor weldability of aluminum alloys determines the challenges of forming quality,internal defects,and the control of microstructures in the forming of aluminum alloy by WAAM.2219 aluminum alloy belongs to Al-Cu-Mn series aluminum alloy.It is widely used in the field of aviation and aerospace because of its high strength,good heat resistance and processing performance.In this study,a double ellipsoidal heat source was used to simulate the temperature field of single-pass ten-layer walls during the WAAM process.The effects of different welding speeds on the microstructure and mechanical properties of the WAAM 2219 aluminum were systematically studied.In addition,in order to refine the structure and eliminate defects such as pores,friction stir processing(FSP)was applied during the WAAM process between layers.Microstructure and tensile properties of the walls manufactured by WAAM with inter-layer FSP after forming and T6 treatment were studied.Single-pass ten-layer walls(length 270mm × width 5.5-8mm × height 23-31.5mm)were fabricated within the welding speed of 400-700mm/min,and the temperature field of the WAAM process was simulated.Comparing the experimental results with the simulation results under the condition of welding speed of 600mm/min,the results show that the measured thermal cycle curves and melting zone characteristics are in good agreement with the simulation results.The maximum temperature of the molten pool increases with the number of layers(n)of the deposited metal and the temperature increase of the molten pool slows down when n?5.The n-th layer of deposited metal is significantly remelted during the deposition of the(n+1)-th layer of metal,and the remelted depth was about 82%of the layer height.The welding speed was increased from 400mm/min to 700mm/min,and the depth of the melting and remelting zone gradually decreased.When the 10th layer was deposited,the depth of the remelting zone was reduced from 5.02mm to 4.01mm,and the depth of the remelting zone was reduced from 2.12mm to 1.81.mm.The straight walls(length 270mm × width 5.5-8mm × height 70mm)of WAAM 2219 aluminum alloy were fabricated with the welding speed of 400-700mm/min,and the effects of welding speed on the forming quality,microstructure and mechanical properties of the straight walls were systematically studied.The results show that average layer height and total wall width of the formed straight walls decrease,effective width coefficient increase,porosity gradually decrease,microstructure of the inter and inner layers is obviously refined as the welding speed increases from 400mm/min to 700mm/min.As the welding speed increases,it had little effect on the tensile strength of WAAM straight wall,while the yield strength and elongation were increased and decreased,respectively.The tensile strength and yield strength are the highest when the welding speed is 600mm/min.The tensile strength,yield strength and elongation of the welding direction(X direction)are 250MPa,98MPa and 17.7%,respectively,while the tensile strength,yield strength and elongation of the building direction(Z direction)are 248MPa,95MPa and 15.4%,respectively.After the straight wall formed at 700mm/min welding speed was treated with T6(530? × 50min+175? × 12h),the average tensile strength and yield strength of the wall in the welding direction(X direction)were 415MPa and 298MPa,respectively.The average tensile strength and yield strength of the wall in the building direction(Z direction)were 346MPa and 194MPa,respectively.But the average elongation in the welding direction(X direction)decreased from 16.5%to 13.7%,and the average elongation in the building direction was reduced from 13.7%to 3.8%.The tensile properties of the walls in the building direction(Z direction)were significantly lower than that in the welding direction(X direction)at all welding speeds.The mechanical properties in the building direction(Z direction)of the walls fabricated by WAAM are mainly attributed to the morphology of the interlaminar eutectic phase and the porosity distribution characteristics.A 2219 aluminum alloy straight wall(length 330mm × width 12mm × height 45mm)was fabricated by using WAAM+inter-layer FSP modification process,that is,a FSP modification was applied after each deposition of n layers(n=3 in this study)of metal until the preset height was reached.In WAAM process,arc swing and forced water cooling were used.Due to the application of inter-layer FSP,the pores in the original sedimentary layer were eliminated,and the dendrite structure was transformed into equiaxed fine grain structure with an average grain size of 5.2 ?m,and the eutectic phase was broken and refined.The average values of tensile strength,yield strength and elongation in the welding direction(X direction)were 279MPa,108MPa and 23.7%,respectively,and those in the building direction(Z direction)were 277MPa,104MPa and 16.4%,respectively.After the same T6 treatment system,the average tensile strength,yield strength,and elongation of the 2219 aluminum alloy straight wall produced by the WAAM+inter-layer FSP process in the welding direction(X direction)are 426MPa,299MPa and 12.0%,respectively,which are close to the tensile properties of 2219 aluminum alloy straight wall prepared by the WAAM process after T6 treatment.The average tensile strength,yield strength,and elongation of the building direction(Z direction)are 382MPa,268MPa and 7.5%,respectively,which is higher than the 2219 aluminum alloy straight wall fabricated by the WAAM process after T6 treatment with 10%increase in tensile strength,38%increase in yield strength and 97%increase in elongation.