MWCNTs/AZ31 surface composites fabricated by friction stir processing

Multi-walled carbon nanotubes (MWCNTs) were successfully dispersed into a magnesium alloy (AZ31) using friction stir processing (FSP). Distribution of the MWCNTs was changed on the basis of the travel speed of the FSP tool. The grain size of the MWCNTs/AZ31 surface composites was smaller than that of the FSPed AZ31 without the MWCNTs. The addition of the MWCNTs appears effective for fabricating the composites consisting of fine matrix grains. The maximum microhardness of these composites was ∼78 Hv, which is almost double that of the AZ31 substrate (41 Hv). It is considered that both the grain refinement of the AZ31 matrix and the reinforcement by the MWCNTs increased the microhardness of the surface composites.