Factors influencing the equilibrium grain size in equal-channel angular pressing: Role of Mg additions to aluminum

Experiments were undertaken to compare the equal-channel angular (ECA) pressing of Al-1 pct Mg and Al-3 pct Mg solid-solution alloys with pure Al. The results reveal both similarities and differences between these three materials. Bands of subgrains are formed in all three materials in a single passage through the die, and these subgrains subsequently evolve, on further pressings through the die, into an array of grains with high-angle boundaries. However, the addition of magnesium to an aluminum matrix decreases the rate of recovery and this leads, with an increasing Mg content, both to an increase in the number of pressings required to establish a homogeneous microstructure and to a decrease in the ultimate equiaxed equilibrium grain size. It is concluded that alloys exhibiting low rates of recovery should be especially attractive candidate materials for establishing ultrafine structures through grain refinement using the ECA pressing technique.