Low cycle fatigue of a rare-earth containing extruded magnesium alloy

The application of ultra-lightweight magnesium alloys inevitably involves fatigue resistance under cyclic loading. The present study was aimed at evaluating strain-controlled cyclic deformation behavior and the relevant effect of microstructure in a rare-earth (RE) element containing extruded Mg–10Gd–3Y–0.5Zr (GW103K) alloy. The microstructure of this alloy consisted of fine equiaxed grains with an average grain size of about 12 μm and a large number of RE-containing precipitates. Unlike the RE-free extruded magnesium alloys, this alloy exhibited essentially cyclic stabilization and symmetrical hysteresis loops without tension–compression asymmetry due to the presence of the relatively weaker texture and the suppression of twinning activities arising from the fine grain size and especially RE-containing precipitates. A detailed analysis for understanding the obstructive role of the precipitate to twinning has been presented. While this alloy had a lower cyclic strain hardening exponent than the RE-free extruded magnesium alloys, it had a longer fatigue life which can also be described by the Coffin–Manson law and Basquinʹs equation. Fatigue crack was observed to initiate from the specimen surface with some cleavage-like facets at the initiation site. Crack propagation was basically characterized by fatigue striations in conjunction with secondary cracks.