Achieving ultrafine grain size in Mg–Al–Zn alloy by friction stir processing

Ultrafine-grained (UFG) microstructures with an average grain size of 100–300 nm are achieved in solution-hardened AZ31 Mg–Al–Zn alloy prepared by friction stir processing equipped with a rapid heat sink. The mean hardness of the UFG region reaches ∼120Hv, which is more than twice as high as that of the AZ31 matrix. The grain refinement kinetics are analyzed and the results are self-consistent.