Superplastic-Like Behavior in Medium Grained and Single Crystalline Al-Mg Solid Solution Alloys

Abstract

High temperature ductility of medium grained and single crystalline Al-6 mol%Mg solid solution alloys has been investigated. It is found that enhanced ductility occurs not only in polycrystalline specimens having grain diameter of 70 μm and 165 μm but also in single crystalline ones in the temperature range above 523 K; maximum elongation for 70 μm grained, 165 μm grained and single crystalline specimens are, respectively, 349%(at 723 K), 322%(at 723 K) and 326%(at 673 K). Experimentally determined strain rate sensitivity index of about 0.3, together with the activation energy for deformation, suggests the solute drag motion of dislocations as a rate controlling process, which in turn is accommodated by the grain boundary sliding. In other words, the high ductility observed here should be referred to as superplastic-like elongation, that is, the phenomenon that has been reported in some solid solution alloys with a large misfit parameter. The fact that the strain rate for largest elongation tends to increase with decreasing grain size may be ascribed to the relative increase in the contribution of grain boundary sliding to the total strain.