Pore suppression and performance improvement mechanisms in wire-arc directed energy deposition of 7075 alloy

The pore defects and grain coarsening are the main reasons for performance deterioration in wire-arc directed energy deposition (DED) of ultra-high-strength aluminium alloy. In this study, experimentation and numerical simulation were performed to investigate the Zn element loss, bubble behaviours, microstructure and performance and effects of wire feeding rate (WFR) in wire-arc DED of 7075 aluminium alloy. The results suggested that both the Zn-bubble and H-bubble did not flow upward directly, but flowed with the molten pool convection. A low WFR decreased the sources of Zn vapour and hydrogen instead of promoting the bubble escape, thus the porosity was decreased (up to 95.8% decrease with WFR = 4 m/min). Meanwhile, it reduced the grain morphology difference, and promoted the dispersed distribution of precipitated phases. After the heat treatment, the optimal performance reached 527.80 MPa of ultimate tensile strength and 7.57% of elongation, approaching the performance level of a forged 7075-T6 plate.