Using two-pass friction stir processing to produce nanocrystalline microstructure in AZ61 magnesium alloy

Despite their interesting properties, nanostructured materials have found limited use as a result of the cost of preparation and the difficulty in scaling up. Herein, a two-pass friction stir processing (FSP) technique is employed to refine grain sizes to a nanoscale. Nanocrystalline AZ61 Mg alloy with an average grain size of less than 100 nm was successfully obtained using FSP. Corresponding to this, the highest microhardness of the nano-grained region reached triple times that of AZ61 substrate. In principle, by applying multiple overlapping passes, it should be possible to produce any desired size thin sheet of nanostructure using this technique. We expect that the FSP technique may pave a way to large-scale structural applications of nanostructured metals and alloys.