Microstructure characterization and corrosion behavior of hollow ZK60 Mg profile containing longitudinal welds

The porthole die extrusion was carried out using ZK60 Mg alloy. The inhomogeneous microstructure was formed on welding and matrix zones of extruded profiles. High extrusion speed induced a temperature rise and made β 1 ’ precipitate disappear, resulting in an obvious grain growth, change of dynamic recrystallization (DRX) mode, and higher DRX degree. The corrosion rate firstly increased due to the occurrence of localized pitting, and then decreased owing to the formation of a denser and more protective film. Low extrusion speed was harmful on the corrosion behaviors, especially in welding zone, due to the smaller grain size and more precipitates. • Inhomogeneous microstructure was formed due to the non-uniform temperature and velocity. • The mode of DRX and number/type of precipitates were depended on extrusion speed. • High extrusion speed increased the size and fraction of DRXed grains in matrix zone. • Corrosion rate firstly increased and then decreased during the immersion of Mg profiles. • Corrosion resistance especially in welding zone was enhanced by high extrusion speed.