Enhanced corrosion resistance of ultrafine-grained AZ61 alloy containing very fine particles of Mg17Al12 phase

Ultrafine-grained (1.1-1.5 μm) AZ61 alloys containing nanoscaled β-Mg17Al12 phase particles (70-140 nm) were prepared using high-ratio differential speed rolling (HRDSR) and their corrosion behaviours were studied in a 0.1 M NaCl solution. The grain size reduction by HRDSR improved the corrosion resistance by enhancing passivity of the surface film. Post-annealing further increased the corrosion resistance by decreasing dislocation density in matrix. When significant grain growth took place, however, the corrosion resistance was decreased because of the pronounced negative effect of the increase in grain size. Refinement of β phase to nanoscale size decreased the susceptibility to microgalvanic corrosion.