Development of Ultra-Fine Grained Structure in an Al-5.4%Mg-0.5%Mn Alloy Processed by ECAP

Microstructural changes during equal channel angular pressing (ECAP) at the temperatures of 250 and 300 C to the strains similar to 4, similar to 8 and similar to 12 were studied in a coarse-grained A1-5.4%Mg-0.5%Mn-0.1%Zr alloy. At a strain of similar to 4, the microstructural evolution is mainly characterized by the development of well-defined subgrains within interiors of initial grains and the formation of fine grains along original boundaries. Further straining leads to increase in the average misorientation angle, the fraction of high-angle grain boundaries and the fraction of new grains. However, only at 300 degrees C, the plastic deformation to a strain of Sigma epsilon similar to 12 leads to the formation of almost uniform submicrocrystalline (SMC) grained structure with an average crystallites size of similar to 0.5 mu m. At 250 degrees C, the microstructure remains non-uniform and consists of subgrains and new recrystallized grains. The mechanism of new SMC structure formation after ECAP is discussed.