Promotion effect of secondary phase particles on grain refinement of deformed Mg-Y-Nd-Zn alloy

The promoting effect of secondary phase particles on the refinement of matrix grains in a series of Mg-Y1.5-Nd0.6-Zn.x (x=0, 0.2, 0.4, 0.8, 1.3) alloys deformed by friction stir processing (FSP) was investigated in this study. The volume fraction of secondary phase in the alloys increased with increment of Zn, and most of the secondary phases were broken into nano-sized particles and dispersed in the matrix during thermal mechanical processing. The resulting fine particles had a remarkable promoting effect on the grain refinement of the Mg matrix during mechanical processing, thermal deformation, and cooling with increasing volume fraction of the secondary phase. For example, the grains of Mg-Y1.5-Nd0.6-Zn1.3 alloy were refined to an average size of 28 nm, compared with the more than 100 nm grain size of the Mg-Y1.5-Nd0.6 alloy.