The correlation between grain structures and the corrosion behaviors of as-extruded Mg-Sm-Zn-Zr alloys

This work investigates the relationship between grain structure and corrosion behaviors of extruded Mg-Sm-ZnZr alloys. The results show that the phase composition and distribution are immune to the varied extrusion ratio, however, the grain orientation, grain boundary, and dislocations are changed, resulting in different corrosion behaviors. The corrosion initiates from the grain boundaries, especially low-angle grain boundaries, and dislocations, while the quasi-passivated surface suppresses the effect of grain orientation. The uniform distributed grain boundaries and dislocations generate uniform protective film with higher corrosion resistance, while the concentrated distribution enhances the film breakdown, causing exposed Mg substrate and accelerated corrosion.