Kinetics of recrystallization in Al-Mg alloys

In order to clarify the effect of Mg on recrystallization of heavily cold rolled Al, Al-Mg alloys containing Mg UP to 5 % were cold rolled 95 % reduction in thickness, and annealed at temperatures between 200 and 450 degrees C. Their recrystallization behavior was investigated with both optical and transmission electron microscopy. It was found that addition of Mg up to 1 % significantly retarded recrystallization, since solute Mg atoms strongly suppressed recovery, nucleation of recrystallized grains and migration of recrystallized high angle grain boundaries. Recrystallization was most strongly suppressed at 1 % Mg, and at Mg content above 1 %, recrystallization was remarkably accelerated with increasing Mg content. Transmission electron microscopy of cold rolled specimens revealed that although well-recovered subgrain structures were formed in pure Al, ill-defined small cell or subgrain structures with high dislocation densities were developed homogeneously in Al-Mg alloys. It was therefore concluded that, in Al-Mg alloys containing Mg more than 1 %, recrystallization was accelerated with increasing Mg content, since dislocation densities and therefore stored energies i.e. driving force for recrystallization was increased with increasing Mg content.