Fatigue of rare-earth containing magnesium alloys: a review

Lightweighting in ground vehicles is today considered as one of the most effective strategies to improve fuel economy and reduce anthropogenic environment-damaging and climate-changing emissions. Magnesium (Mg) alloy, as a strategic ultra-lightweight metallic material, has recently drawn a considerable interest in the transportation industry to reduce the weight of vehicles due to their high strength-to-weight ratio, dimensional stability, good machinability and recyclability. However, the hexagonal close-packed crystal structure of Mg alloys gives only limited slip systems and develops sharp deformation textures associated with strong mechanical anisotropy and tension-compression yield asymmetry. For the vehicle components subjected to dynamic loading, such asymmetry could exert an unfavourable influence on the material performance. This problem could be conquered through weakening the texture via addition of rare-earth (RE) elements. Thus, a number of RE-containing Mg alloys have recently been developed. To guarantee the structural integrity, durability and safety of highly loaded structural components, understanding the characteristics and mechanisms of cyclic deformation and fatigue fracture of such RE-Mg alloys is of vital importance. In this review, the available fatigue properties including stress-controlled fatigue strength, strain-controlled cyclic deformation characteristics and fatigue crack propagation behaviour are summarized, along with the microstructural change and crystallographic texture weakening in the RE-containing Mg alloys in different forms (cast, extruded and heat-treated states), in comparison with those of RE-free Mg alloys.