Influence of crystallographic orientation and Al alloying on the corrosion behaviour of extruded α-Mg/LPSO two-phase Mg-Zn-Y alloys with multimodal microstructure

A highly corrosion resistant Mg-Zn-Y-Al alloy featuring an α-Mg/LPSO two-phase multimodal microstructure was developed. The extruded Mg-Zn-Y alloy showed orientation dependent corrosion behaviour, the longitudinal section exhibited a higher corrosion rate than the transverse section. The orientation dependence was attributed to the varying in-plane atomic densities of the crystallographic planes on the longitudinal and transverse sections. The LPSO phase was the cathode and galvanic corrosion occurred in the adjacent α-Mg. The Al alloying into the Mg-Zn-Y alloy facilitated the formation of a protective surface film, which decreased the corrosion rate in spite of geometrical and electrochemical heterogeneities.