Research On The Process And Properties Of Multi-Wires GMAW Additive Manufacturing Of High-Strength Aluminum Alloy

The 7000 series high-strength aluminum alloy is widely used in the manufacturing of structural components of the aerospace field.However,the overall structure of aviation components with large size and complicated structure.The traditional reducing processes have the disadvantages of low flexibility and material waste.Therefore,wire arc additive manufacturing（WAAM）technology with low cost,high efficiency,and strong flexibility has shown significant potential and advantages.However,high-strength aluminum alloys with high strength and poor plasticity,it is difficult processed into the wire used for WAAM.Therefore,based on the principle of in-situ alloying,a new method of heterogeneous multi-wires arc additive manufacturing for Al-Zn-Mg-Cu alloy is proposed.The Al-6.0Zn-2.5Mg-2.5Cu and Al-6.0Zn-2.5Mg-1.5Cu alloys are as design objectives,and the process,microstructure and property,and numerical simulation were researched.Firstly,based on the GMAW wire arc additive manufacturing system,a multi-wire WAAM system was builted by adding tooling fixtures and wire feeding mechanisms.In order to satisfy the forming requirements of multi-wire additive manufacturing components,the relative position and angle of the three wires were explored.After that,the effects of current and additive manufacturing speed on the forming quality of single layer and single pass deposition layers were analyzed,and the WAAM Al-6.0Zn-2.5Mg-2.5Cu alloy process parameters were chosen for thin wall components.The microstructure and mechanical properties of Al-6.0Zn-2.5Mg-2.5Cu alloy components were analyzed.The results of X-ray diffraction（XRD）showed that the the main precipitates in the components isη（Mg（Al,Zn,Cu）₂）phase.The microstructure consists of columnar crystals and coarse equiaxed grains,bounded by the fusion line.The upper portion of a deposition layer is mostly coarse equiaxed grains,while the lower portion is mostly columnar crystals.The microhardness of the components fluctuates in the range of110HV-130HV.Penetrating cracks and cluster porosities near the fusion line were found in the component,which had an impact on the tensile properties of the component.The main reason for the occurrence of thermal cracks and cluster porosities is that the unified regulation mode of the GMA inverter power supply makes it impossible to achieve decoupling control between the current and the single wire feeding speed,resulting in insufficient heat input during the deposition process of the three wires,leading to the appearance of thermal cracks and cluster porosities defects near the fusion line,which affects the tensile performance of the components.Aiming at the problem of insufficient heat input,the heat input is further increased by reducing the wire feeding speed and welding speed of the bypass ER2319 welding wire,thereby improving the metallurgical reaction of the three wires.The microstructure distribution of Al-6.0Zn-2.5Mg-1.5Cu alloy components manufactured with improved processes is consistent with Al-6.0Zn-2.5Mg-2.5Cu alloy,and the average grain size obtained from EBSD results is 57μm.The second phase in the alloy are determined asηPhase（Mg（Al,Zn,Cu）₂）andη′Phase by HRTEM.The average microhardness of components was 118 HV.The average tensile strength in the horizontal direction is266.7MPa,with an elongation of 2.7%.The average tensile strength in the vertical direction is 250.7MPa,with an elongation of 2.3%.Compared with WAAM Al-6.0Zn-2.5Mg-2.5Cu alloy components,the thermal cracking and porosity problems have been significantly improved.Finally,the numerical simulation of the WAAM process of Al-Zn-Mg-Cu alloy under two sets of different heat input was carried out.The simulation results of the temperature field show that the Al-6.0Zn-2.5Mg-1.5Cu alloy component has a larger melting depth and a slower cooling rate.The decrease in cooling rate in the melt pool effectively improves the porosity problem of the component.The residual stress distribution and deformation degree of the components under two different heat input conditions are consistent.The residual stress and deformation values on both ends of the deposition layer are relatively large,while the middle area is relatively small.The phenomenon of interlayer cracking and warping deformation exhibited by the prepared Al-6.0Zn-2.5Mg-2.5Cu alloy components is consistent with simulation results.The correlation between heat input and defect generation has been verified again through simulation,which can provide reference for the design of multi-wires arc additive manufacturing process parameters.