Creep and hot working of Mg alloy AZ91

Die cast Mg alloy AZ91 has been subjected to creep (< 10(-4)s(-1)) in both compression and tension and to hot working (10(-2)-10 s(-1)) in torsion. Constitutive analysis showed that the dependencies of maximum deformation resistance (minimum creep rate at constant stress or maximum flow stress at constant strain rate) on temperature T were fairly consistent across the entire range. The total creep strains within the operating life were compared to behavior of AS21. The torsion tests were concerned with the dependence of fracture strain on T and <(<epsilon>)over circle> and were compared to the behavior of AZ31. Twinning took place at low strains to reorient grains not suited for slip and occurred much more profusely in the hot working. As a result of dynamic recovery, subgrains developed primarily near the grain boundaries, being much larger in creep than those in hot working consistent with the stresses. In the creep specimens, the particles underwent considerable change over long periods, reducing the strain resistance. In contrast, during hot working the specimens underwent dynamic recrystallization that gave rise to considerably improved ductility and reduced strength at high T.