A comparative study on microstructure and mechanical properties of wire-arc directed energy deposited Al–Zn–Mg–Cu alloy based on the cold metal transfer technology

Abstract

Wire-arc directed energy deposition (DED) of Al–Zn–Mg–Cu alloy faced a tough challenge because of the occurrence of crack and pore defects caused by the high content of alloying elements. Three cold metal transfer (CMT) arc modes were studied to fabricate Al–Zn–Mg–Cu alloy components via the wire-arc DED process, with the aim of optimizing the deposition process and revealing the action mechanism of arc mode on the microstructure and mechanical properties. The effect of the CMT arc mode on the forming accuracy and arc/droplet behaviors was investigated with the assistance of the microscope and high-speed camera. The characteristics of grain morphology, crystallographic texture, and precipitated phase were quantitatively analyzed. The results show that the forming accuracies of deposited samples degenerate when using CMT and CMT pulse modes due to abnormal electrical waveforms and overflow/curve phenomenon. The finest grain size is realized under CMT advance mode because of its induced stirring effect on the molten pool, expanded constitutional supercooling zones, and extremely low heat input. The continuous and coarse precipitated phases in CMT and CMT pulse modes are transferred into dispersive ones in CMT advance mode. Moreover, the quantity and size of pores are also reduced in CMT advance mode. The combined action of microstructure optimization and defect reduction is conducive to improving the mechanical properties. Finally, the preferable ultimate tensile strength (∼278.15 MPa) and top elongation (∼6.50 %) of as-deposited Al–Zn–Mg–Cu alloy are achieved.