Research On The In-situ Alloying Process And Mechanism Of Aluminum Alloy Manufactured By Multi-Wire Indirect Arc

A new heterogeneous twin-wire indirect arc in-situ synthesis process for Al-Zn-Mg-Cu alloy was developed to address the issues of the lack of mature commercial welding wires and low forming efficiency in the Al-Zn-Mg-Cu alloy arc additive manufacturing.Heterogeneous twin wires（Al-Cu and Al-Mg）and a bypassing Zn wire were used to achieve in-situ additive manufacturing of Al-Zn-Mg-Cu alloy.The arc behavior and droplet transfer of heterogeneous twin-wire indirect arc,the process of heterogeneous indirect arc in-situ synthesis,and the microstructure and properties analysis of Al-Zn-Mg-Cu alloy produced by heterogeneous multi-wire indirect arc additive manufacturing were researched in this thesis.Aiming at the problem that the stable process interval of the indirect arc in the‘point-to-point’mode is difficult to determine,the theoretical analysis of the force acting on the twin-wire indirect arc,the force acting on the droplet,the energy transfer and the arc deflection is carried out based on the electromagnetic theory and mechanics theory.The influence of the angle between the twin wires,the current amperage and the wire feeding speed on the stability of the twin-wire indirect arc was obtained.Experimental research found that as the angle between the two wires decreased,the electromagnetic force acting on the arc increased and the arc stiffness increased.The current amperage increased,the arc length gradually increased,and the droplets transfer mode produced by the anode welding wire were spray transfer,and the droplets transfer mode produced by the cathode welding wire were globular transfer.When 2319 welding wire was used as the anode and 5356 welding wire was used as the cathode,with a twin-wire angle of 90°,and the wire feeding speed matched with the current amperage,the arc burned stably with a‘heart’shape.When the wire feeding speed did not match the current amperage,the arc deflection occurred,leading to the deterioration of arc stability which was consistent with the theoretical analysis law.The process of heterogeneous twin-wire indirect arc in-situ synthesis was explored based on the determined process parameters for stable arc.The effects of wire feeding speed and additive manufacturing speed on the morphology of single-layer single-pass forming were obtained through single layer forming process experiments.An Al-Mg-Cu alloy was prepared by heterogeneous twin-wire indirect arc multi-layer deposition.The alloy containedα-Al and S（Al₂Cu Mg）phases.The average hardness of the alloy was 73.7HV,and the average tensile strength parallel and perpendicular to the building direction were 224.6 MPa and 235.2 MPa,respectively.The feasibility of in-situ synthesis of target alloy by heterogeneous twin-wire indirect arc additive manufacturing was verified.The heterogeneous three-wire indirect arc additive manufacturing experiments for in-situ alloying of Al-Zn-Mg-Cu alloy were carried out based on the research heterogeneous twin-wire indirect arc additive manufacturing.The Al-5.7Zn-3.4Mg-1.6Cu（wt.%）alloy was formed by in-situ metallurgical reaction.The alloy contains second phases such as S（Al₂Cu Mg）,η（Mg（Al,Zn,Cu）₂）andη′.The composition ratio and constituent phases are in accordance with the targeted Al-Zn-Mg-Cu alloys.The interlayer region of the sample existed a fusion line composed of fine equiaxed and cellular grains,with columnar and equiaxed grains distributed at the upper and lower sides of the fusion line,and inclined columnar crystals dominating in the center region.Due to the high wire melting efficiency（5.1 kg/h）,the single layer deposition size is large,the undercooling of the sample is small during additive manufacturing,resulting in large grain size.The average grain size of the center and interlayer of the middle region is 146.2μm and 126.0μm,respectively.The average hardness,tensile strength,and elongation of the samples were 98.6 HV,243.9 MPa,and 5.9%,respectively,which were slightly higher than those of the cast 7050 aluminum alloy.The in-situ synthesis of Al-Zn-Mg-Cu alloy was achieved by heterogeneous multi-wire indirect arc additive manufacturing.