Achieving high productivity in wire-arc directed energy deposition of magnesium alloy thin-walled structures via active cooling

Wire-arc directed energy deposition (DED) with high heat input typically requires long inter-pass intervals to avoid deteriorating metallurgical and mechanical properties. However, this significantly extends process time, thereby sacrificing the manufacturing rate (MR). This trade-off is particularly pronounced in thin-walled structures due to low heat dissipation. While solid-contact active cooling (SCAC) can improve the metallurgical and mechanical properties of magnesium alloys in wire-arc DED, its potential for aggressive MR enhancement remains under-explored. This study experimentally reveals that SCAC enables the fabrication of AZ31 thin walls with a refined microstructure and acceptable tensile properties even under a very short interval (average 2.5 s) corresponding to an extremely high MR (882 cm 3 /h). While natural cooling (NC) exhibited continuous heat accumulation leading to bead sagging despite a 120 s interval (MR = 90 cm 3 /h), SCAC reached thermal equilibrium early, enabling nearly continuous deposition. Additionally, narrowing the gap between the cooling copper blocks reduced the molten pool volume. Furthermore, the refinement of grains and precipitates by SCAC promoted a transition from a predominant quasi-cleavage mode to an extensive ductile fracture mode. Consequently, SCAC increased the yield strength, tensile strength, and elongation by up to 12 MPa, 13 MPa, and 10%, respectively, along the travel direction. Microstructural analysis suggests that the yield strength enhancement is primarily governed by grain refinement. This work demonstrates that active cooling strategies, including but not limited to SCAC or magnesium alloys, possess the potential to maintain the overall mechanical properties while significantly enhancing productivity in wire-arc DED.