Development of Ultra-Fine Grained Structure in an Al-5.4 %Mg-0.5 %Mn Alloy Subjected to Severe Plastic Deformation

It was shown that extensive grain refinement takes place in an as-cast Al-5.4%Mg-0.5%Mn-0.1%Zr alloy subjected to severe plastic deformation under multi-directional forging up to a total true strain of similar to 9 at 250 and 300 degrees C. At a strain of similar to 3, the deformed microstructure is mainly characterized by the formation of new grains along original boundaries and the development of well-defined subgrains within interiors of original grains. Upon further straining the misorientation of deformation-induced boundaries increases; new grains appear homogeneously both within grain interiors and along original boundaries. Decreasing temperature accelerates the transformation of low-angle boundaries (LABs) into high-angle boundaries (HABs). The resulted grain size evolved in this alloy was slightly less than that produced in an Al-6%Mg-0.35%Sc by severe plastic deformation under similar conditions. In addition, in the alloy belonging to Al-Mg-Mn-Zr system the formation of a fully recrystallized structure was found at a lower cumulative strain in comparison with the alloy belonging to Al-Mg-Sc system. This unusual difference associated with the fact that the Al-5.4%Mg-0.5%Mn-0.1%Zr alloy was initially subjected to solution treatment at a relatively low temperature of similar to 360 degrees C. Effect of homogenization annealing on phase composition of this alloy is discussed. [doi:10.2320/matertrans.L-MZ201115]