Periodic strain burst behaviour of Al0.87 Mg alloy in cyclic creep at intermediate temperatures

Abstract

Intermediate-temperature cyclic creep of Al0.87% Mg alloy under different cyclic peak stresses was studied. In the secondary creep stage, periodic strain bursts occurred only in a certain region of both stress and temperature. The threshold stress of strain burst appearance was found to be almost independent of temperature, but its temperature range for a constant stress decreased with increasing applied stress. The period of strain bursts decreased with increase in both stress and temperature, whereas their amplitude changed with stress only. The average creep rate during strain bursts was observed to be more sensitive to both stress and temperature than that during conventional creep. A new model on strain bursts is proposed based upon the strain equation in terms of mobile dislocation density and also the collective motion of pile-up dislocations in front of forest dislocations under concentrated stress. Relationships of strain burst period and amplitude with (i) temperature, (ii) cyclic peak stress, (iii) average creep rate and finally (iv) cyclic stress frequency have been deduced and also verified by the experimental results.