Microstructural evolution in the ultrafine-grained surface layer of Mg-Zn-Y-Ce-Zr alloy processed by sliding friction treatment

A nanocrystalline surface layer with average grain size of 98 nm of Mg-6Zn-0.2Y-0.4Ce-0.5Zr (wt%) alloy was fabricated successfully by sliding friction treatment (SFT). The abundant second-phase particles are heavily broken and homogeneously distributed in the matrix after SFT. Electron backscattered diffraction (EBSD) indicates that the intensity of basal texture shows a gradually decreasing trend with the decreasing distance from the treated surface due to the new recrystallized grains with random grain orientation. The process of grain refinement is found to involve the following stages: (i) the twins and dislocations are activated under the low strain area; (ii) the high density of dislocations accumulated near the second-phase particles promote the formation of substructures and the shear bands; (iii) the increasing strain arouses the transformation of substructures; (iv) multiple stacking faults will induce the nucleation of new strain-free grains under the high strain; (v) the nanosized grains are acquired. The abundant fine second-phase particles give large contribution for the refining process due to the pinning effect on the dislocations.