Fatigue characteristics of the extruded AZ80 automotive wheel

Abstract

In order to provide a reliable theoretical foundation for fatigue resistant design of the magnesium alloy automobile wheel, specimens machined from rim and disc of the extruded AZ80 wheel were subjected to strain-controlled fatigue tests. Various characterizations (such as microstructure and texture analysis, stress-strain response monitoring, twinning/detwinning behavior evolution, and fatigue fracture morphology analysis) have been carried out to investigate the static and fatigue performance of the AZ80 wheel. The obtained microstructural analysis revealed that the rim sample exhibited finer and more homogeneous dynamic recrystallized grains with the average grain size of ~17.2 μm, while ~30.5 μm for the disc sample. The rim specimen achieved the ultimate tensile strength of ~339 MPa with a noticeable elongation to fracture of ~14.6%. In addition, the rim sample also showed superior fatigue properties as compared with the disc sample, which was related to the smaller grains and the weaker texture intensity. The twinning/detwinning behavior participated in the cyclic deformation above the strain amplitude of 0.4% for both samples, resulting in asymmetric hysteresis loops and residual twins. The fatigue crack initiation site was observed with second phase particles and secondary cracks near the surface for all specimens, and in particular, cleavage-like faceted area with twins was identified at strain amplitude of 1%.