Factors influencing the flow and hardness of materials with ultrafine grain sizes

Ultrafine grain sizes were introduced into an Al-3wt%Mg solid solution alloy and a commercial Al-Mg-Li-Zr alloy through intense plastic straining by equal-channel angular (ECA) pressing at room temperature and at 673 K respectively. Tensile testing of pressed samples at room temperature revealed markedly different stress-strain curves for these two alloys, with the Al-3wt%Mg alloy exhibiting a high yield stress with little subsequent strain hardening and the Al-Mg-Li-Zr alloy exhibiting a lower yield stress and extensive strain hardening after yielding. These and other experimental results are interpreted in terms of the nature of the microstructure introduced by the ECA pressing procedure. It is concluded that significant variations may occur in the mechanical properties of nominally similar ultrafine-grained materials depending upon the pressing conditions and the extent of any relaxation which may occur during the straining process.