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 Basquin's 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.