Effect of Cyclic Stress Reduction on the Creep Behaviour of Al-Ag and Al-Ag-Zr Alloys Containing γ′ and γ Precipitates

Abstract

Creep tests under the effect of cyclic stress reduction were conducted to Al-16 wt%Ag and Al-16 wt%Ag-0.1 wt%Zr alloys aged at 548 and 673 K. The steady state creep rate was found to be higher under cyclic stress reduction condition than that under static creep condition for the same maximum stress. An expression for the temperature dependence of the threshold stress for cyclic creep acceleration is offered. Cyclic creep acceleration is interpreted using the dislocation cross-slip model. TEM investigations confirmed that the addition of Zr to Al-Ag alloy accelerates the formation and coarsening of γ′ and γ-phases. The mean value of activation energy for both alloys aged at 548 K was found to be 35±0.3 kJ/mol, and 58±0.4 kJ/mol for alloys aged at 673 K.