Low cycle fatigue and fatigue-creep interaction effects on softening behavior and life prediction of cast aluminum alloy at elevated temperature

In this study, a series of strain-controlled low-cycle-fatigue (LCF) and low-cycle-fatigue-creep (LCFC) experiments were conducted on a cast Al-Si-Cu alloy. LCF and LCFC experiments were performed at 250 ℃, 300 ℃ and 350 ℃ with three different strain amplitudes. The results showed significant softening behavior, with temperature affecting both the softening behavior and fatigue life. Interestingly, coupling creep at 250 ℃ was found to increase fatigue life. Microstructure evolution was investigated by using scanning electron microscopy, and it was found that the introduction of strain-dwell at the tensile peak caused the interaction of fatigue and creep, resulting in a large amount of plastic deformation that affected fatigue life. Two fracture models were proposed for LCF and LCFC tests at different temperatures, based on the microstructure evolution. Using the experimental data, a modified life prediction model was proposed, which demonstrated a better prediction ability than other traditional models in fatigue-creep life prediction under different temperature and strain amplitudes.