Daolun L. Chen

Abstract:

One of the most effective solutions for reducing environment-damaging emissions and improving fuel economy is to implement lightweight materials in ground vehicles. With the ultra-lightweight feature, high strength-to-weight ratio and superior damping capacity, magnesium has recently emerged as a promising material in the lightweight design and construction for energy efficiency in the automotive and aerospace industry. Despite the potential of substantial reductions in weight, most wrought magnesium alloys exhibit a high degree of mechanical anisotropy and tension-compression yield asymmetry due to the presence of strong crystallographic texture owing to their hexagonal close-packed structure and limited deformation modes. For the vehicle components subjected to dynamic cyclic loading, such problems could exert an unfavorable influence on the material performance. These problems could be tackled through texture modification via alloy composition adjustment, i.e., an addition of rare-earth (RE) elements into magnesium alloys. Despite the fact that the addition of RE elements sheds some light on the alteration in the mechanical anisotropy, the potential advantage of such RE-Mg alloys as structural components under cyclic loading condition has not been well appreciated. An understanding of cyclic plastic deformation is essential for the critical engineering application of Mg-RE alloys. The aim of the present study was, therefore, to identify the cyclic deformation characteristics of RE-Mg alloys under varying strain amplitudes, with particular attention to the effect of RE elements. It was found that the Mg-RE alloy contains a large number of precipitates and possesses a fairly weak texture, which gives rise to much relieved tension-compression yield asymmetry and enhanced fatigue fracture resistance in comparison with the RE-free extruded Mg alloys. The fatigue life of the present alloy was observed to be longer than that of the RE-free extruded Mg alloys. Details about the cyclic deformation behavior of RE-Mg alloys will be presented.