Corrosion of Extruded Mg Alloys: Effect of Major Alloying Elements

Vehicle lightweighting has been a key driver for vehicle manufacturers to reduce the carbon emission of the internal combustion engine and to increase the range of electric vehicles (Joost and Krajewski, Scr Mater 128:107–112, 2017). Mg alloys are one of the competitors in automotive applications (Shi et al. Sci Rep 10:10044, 2020; Luo et al. JOM 73:1403–1418, 2021). The objective of this work was to determine the corrosion susceptibility of three Mg alloy extrusions in NaCl (aq) and the role played by the major alloying elements. Alloys under study include AM30 (Mg-3Al-0.4Mn), ZE20 (Mg-2.4Zn-0.2Ce), and ZAEXM11000 (Mg-1Zn-1Al-0.2Ce-0.2Ca-0.4Mn). Cross-sectional examination of the extruded microstructures using microscopy techniques revealed two distinct metallurgical zones: (i) recrystallized coarse-grained skin layer and (ii) an uncrystallized fine-grained core. The relative corrosion susceptibility of each zone, as a starting surface, was investigated using potentiodynamic polarization and volumetric H2 gas evolution as a function of immersion time in 0.1 M NaCl (aq).