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 pet Mg and Al-3 pet Mg solid-solution alloys with pu re Al. The results reveal both similarities and differences between th ese three materials. Bands of subgrains are formed in all three materi als in a single passage through the die, and these subgrains subsequen tly evolve, on further pressings through the die, into an array of gra ins 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 pressi ngs required to establish a homogeneous microstructure and to a decrea se in the ultimate equiaxed equilibrium grain size. It is concluded th at alloys exhibiting low rates of recovery should be especially attrac tive candidate materials for establishing ultrafine structures through grain refinement using the ECA pressing technique.