Effect of cyclic stress on the high temperature creep behavior of AlMg alloys

Abstract

The effect of cyclic stress on high temperature creep and also the dislocation structures developed during cyclic creep for three AlMg solid solutions have been studied. When the steady state creep rate is the range of 10 −8 s −1, cyclic creep with complete unloading ( R = 0) exhibited only the transition from class M to class A creep instead of the two transitions from class M to class A and then to class M again ihe corresponding static creep. The threshold stress for the transition in cyclic creep was found to be close to or larger than that for the class A to class M transition in the static creep. With increase in magnesium content, cyclic creep retardation became stronger at lower stresses. However the transition from retardation to acceleration in the cyclic creep has been observed at higher stress levels only in the high magnesium alloys. Also found were two types of relationships between the unloading amount and steady state creep rate. The micromechanisms of cyclic creep, especially the interaction of dislocations with solute atoms, have also been discussed.