Effect of strain ratio on cyclic deformation behavior of a rare-earth containing extruded magnesium alloy

Cyclic deformation characteristics of an extruded Mg–10Gd–3Y–0.5Zr (GW103K) magnesium alloy were determined via the strain-controlled low cycle fatigue tests with varying strain ratios at a constant strain amplitude. Unlike the rare-earth (RE)-free extruded magnesium alloys, the present alloy exhibited symmetrical hysteresis loops in tension and compression in the fully reversed strain-control tests at a strain ratio of Rε=−1. This was due to the presence of relatively weak crystallographic textures and the suppression of twinning–detwinning activities arising from the fine grain sizes and RE-rich particles. At a strain ratio of Rε=0 and 0.5, a large amount of plastic deformation occurred in the tensile phase of the first cycle of hysteresis loops due to the high positive mean strain values. With decreasing strain ratio, the hysteresis loops became wider. Fatigue life of this alloy was observed to be the longest in the fully reversed strain control at Rε=−1, and it decreased as the strain ratio was deviated from Rε=−1. A certain degree of mean stress relaxation was also observed in the non-fully reversed strain control (i.e., Rε≠−1 tests).