Effect of the active cooling and dwell time to tensile properties of AZ31 wall components by wire-arc directed energy deposition

Wire-arc directed energy deposition (DED) has been a promising additive manufacturing technology for safety and rapidly fabricating magnesium (Mg) alloy components. However, high heat input from the electric arc can degrade geometric accuracy and cause grain coarsening. This is a critical issue for Mg alloys because their mechanical properties are strongly influenced by grain size. One common solution is to pause the deposition process until the component cools to an appropriate temperature, which significantly reduces the manufacturing rate. To address this issue, our study proposes a novel active cooling method for the Mg alloy deposition process: solid-contact active cooling (SCAC). This method involves direct contact between copper blocks and the fabricated component. We fabricated AZ31 alloy walled components using three cooling methods: no active cooling (NAC), SCAC with copper blocks (SCAC-C), and SCAC with internal water circulation (SCAC-W). The manufacturing rate reached up to 364 cm³/h. NAC with a short interpass dwell time resulted in frequent weld sagging, coarser grains, and decreased tensile properties. In contrast, SCAC-C with a short interpass dwell time led to finer grains and improved surface quality, even though the copper blocks reached 500℃. The SCAC-W was the most effective, as the water-cooled copper blocks remained below 50℃, resulting in the finest grains and the best tensile properties. These results demonstrate that the SCAC method, particularly the SCAC-W, can prevent grain coarsening and degradation of tensile properties while achieving a significantly higher manufacturing rate.