Microstructural evolution of AZ31 Mg alloy with surface mechanical attrition treatment: Grain and texture gradient

Nanocrystalline surface layers and gradient nanostructures are produced in AZ31 Mg alloy through surface mechanical attrition treatment (SMAT). The grain sizes in the surface layer of the alloy are significantly refined to a nanoscale after SMAT. A gradient nanostructure is formed in which the grain size increases gradually from surface to matrix. The microhardness of the surface layer and the tensile strength of the alloy are significantly improved, but with a certain loss of fracture elongation. SEM photographs of tensile fracture of samples after SMAT show that the fractures of the GNS layer are brittle fractures with poor toughness, while the plasticity of the matrix is better, and the fractures exhibit typical ductile features. To investigate the effect of SMAT on the textural evolution of AZ31 Mg alloy, electron backscatter diffraction is used to analyze the as-received sample and samples after SMAT. The non-basal plane orientation is increased and the basal texture is significantly weakened in the fine-grained layer after SMAT. The weakening of the basal texture reduces the anisotropy of the mechanical properties of Mg alloys, which is beneficial for their industrial application. (C) 2020 Published by Elsevier B.V.