On creep behavior in powder metallurgy 6061 Al

An analysis of recent creep data on PM 6061 Al in terms of creep rate against effective stress suggests that the creep behavior of the alloy exhibits a transition from viscous glide to a high-stress region whose advent is related to the breakaway of dislocations from their solute atom atmospheres. This suggestion is supported by the following: (a) the close correspondence between activation energies estimated from experimental data and those reported for Al-based solid-solution alloys, (b) the good agreement between theory and experiment in the viscous glide region, and (c) the consistency between experimental data and the glide/climb criterion. On the basis of the present analysis, it is predicted that a transition in the creep behavior of PM Al alloys and their discontinuous composites from that of Class I (alloy Class) to that of Class II (metal Class) may occur when the effective stress is reduced below a critical value. This critical value for the effective stress is in part determined by the value of the threshold stress for creep which in turn is controlled by the volume fraction of oxide particles introduced in PM Al alloys and their discontinuous composites by powder metallurgy. In general, the above prediction should also be valid for solid-solution alloys that contain nanometer-scale stable particles.