Sub-structure strengthening and work hardening of an ultra-fine grained aluminium–magnesium alloy

The mechanical properties of an Al–Mg1 alloy, processed to obtain grain sizes in the range from less than a micrometer to relatively coarse sizes, have been investigated by tensile and compression testing. A characteristic feature of the stress–strain curves of fine-grained Al–Mg-alloys is a sharp yield point followed by Lüders-band elongation. The flow stress at each given strain level followed a Hall–Petch type grain size dependence. However, the slope of the Hall–Petch curve is larger at the yield point than at strains beyond the yield-point elongation. The compression testing revealed a new phenomenon, namely that the range of stage-III deformation decreased with decreasing grain size, and disappeared completely for a grain size of about 0.5 μm.