MECHANISM OF HIGH-TEMPERATURE CREEP OF ALUMINUM-MAGNESIUM SOLID-SOLUTION ALLOYS

The purpose of the study described was to examine and develop the creep theory of alloys proposed by J. Weertman. Al-Mg alloys with 0 to 6. 9 at. % Mg were creep tested at 328 to 461 C under 0. 20 to 7 kg/sq mm stress. A creep rate equation was derived. Transmission electron microscopy was used to examine the substructure and the density of dislocations during creep. Transient deformation behavior after a sudden stress change was included in the investigation. It is concluded that the high temperature creep rate of alloys is controlled by the viscous motion of dislocations and is proportional to the cube of the stress, provided that the following conditions are satisfied: a large atom misfit parameter, a rather high solute concentration, a high stacking fault energy, and a uniform distribution of dislocations. Therefore, the high temperature creep rate of solid solution alloys is not always controlled by the viscous motion of dislocations.