Grain size and texture effects on deformation behavior of AZ31 magnesium alloy

Cold rolled AZ31 magnesium alloy sheet was subjected to friction stir processing to generate four average grain sizes ranging from 0.8 to 9.6μm. The processed material exhibited a strong basal fiber texture with the c-axis tilted about 35–55° towards the processing direction. The grain size and texture dependence of mechanical behavior were evaluated by using tensile testing along two orthogonal directions. Remarkably high ductility of ∼65% was achieved in relatively coarse grained material that fractured without developing necking when tested in the processing direction. The ductility decreased significantly to ∼10% for ultrafine grained material as the tensile yield strength increased from ∼53MPa to ∼180MPa. Grain size had limited influence on ductility of processed material tested in transverse direction, but reduced the uniform elongation to ∼2% for ultrafine grained material which exhibited ∼320MPa yield strength. Accompanying the significant anisotropy in tensile strength in two directions, the deformation of processed AZ31 in the processing direction was mainly accommodated through basal slip and extension twinning (except for ultrafine grained material); however, the deformation of material in transverse direction was dominated by non-basal slip. Influences of grain size and texture on mechanical behavior were studied in terms of work-hardening and deformation mechanisms.