Control of fine grain structures and strengthening-toughening mechanisms in magnesium alloys fabricated by wire-arc directed energy deposition

• A novel spiral oscillation (SO) strategy during WA-DED of AZ31 Mg alloy significantly enhances strength-ductility synergy, with YS, UTS, and elongation improved by 9.7%, 38.1%, and 147%, respectively. • The SO strategy promotes columnar-to-equiaxed transformation (CET) and reduces maximum texture intensity by 74.2%, leading to refined microstructure and reduced mechanical anisotropy. • Second-phase particles, primarily Al8Mn5 and Al8Mn4Y, are more uniformly distributed, contributing to the improved mechanical properties. • This work provides a promising pathway for microstructural control in WA-DED Mg alloys, expanding their application potential in lightweight structural components.