Mg alloy sheets with a nanocrystalline surface layer fabricated by wire-brushing

Wire-brushing was applied under varying conditions to surfaces of AZ31B Mg alloy sheets for the purpose of grain refinement. The microstructure, mechanical properties and corrosion resistance of the wire-brushed Mg sheets were investigated. The thickness of the maximum deformed areas from the wire-brushed surfaces were about 20 μm, and the deformed areas near the surfaces each consists of nanocrystals and ultrafine grains. A nanocrystalline surface layer consisted of equiaxed nanocrystals smaller than 100 nm, with the smallest mean grain size being 68.2 nm. The mean grain size in the nanocrystalline layer depended on the feed speed rather than the pressing load of the wire-brushing. Powdery Mg debris, which were produced at the surface of the sheet during wire-brushing, moved several millimeters during the wire-brushing. The 0.2% proof stress and tensile strength slightly increased after the wire-brushing, although the elongation decreased. The corrosion resistance of the wire-brushed sheet was approximately 4 times higher than that of the starting sheet.