Influence of hot rolling and evolved microstructure on high cycle fatigue behaviour of Mg-4Zn-4Gd alloy

Abstract

The high cycle fatigue behaviour of bulk nanostructured Mg-4Zn-4Gd magnesium alloy, produced through hot rolling with different reductions such as 50% (corresponding true strain, εT −0.693), 75% (εT, −1.386) and 85% (εT, −1.897) was investigated. The solution treatment of the alloy was performed at 673 K for 24 h in order to achieve equiaxed microstructure prior to rolling. The microstructural characteristics of the alloy were examined through light microscopy. The influence of several microstructural features such as dislocation, deformation twins, micro/nano-precipitate, and ultrafine grains on tensile and hardness behaviour is used to understand fatigue life (Nf) of the processed material. Along with microstructural aspects, the effects of varying applied stress amplitude (σa) and cyclic hardening zone were also analysed to quantify its influence on fatigue life of the rolled materials. The 75% hot rolled specimen has shown maximum fatigue life (i.e. ≥ 1.5 × 106) at 75 MPa stress amplitude. The associated fracture mechanism was explored through scanning electron fractography for the specimen subjected to HCF regime. All the fatigue influencing factors were characterised by using transmission electron microscopy along with X-ray results.