Thermo-mechanical fatigue behavior and life prediction of the Al-Si piston alloy

The thermo-mechanical fatigue (TMF) behaviors and corresponding damage mechanisms of Al-Si piston alloy were investigated in the temperature ranges of 120-350 degrees C and 120-425 degrees C in this study. For TMF cyclic stress response behavior, the rapid cyclic softening occurs in the initial stage and then the cyclic stress maintains stable at lower strain amplitudes; but the cyclic stress displays gradual decrease up to the final failure at higher strain amplitudes. For TMF damage behavior, the cracks mainly initiate from the broken primary silicon in the temperature of 120-350 degrees C range, and commonly nucleate from the boundary between primary Si and matrix in the temperature of 120-425 degrees C range. For both cases, creep may have obvious influence and result in the formation of many micro-voids, but the oxidation may only have a little effect. A new energy-based model for low-cycle fatigue (LCF) and TMF life prediction was proposed based on the hysteresis energy with strain rate modification, considering both fatigue and creep damages. The predicted results agree well with the experimental ones for the Al-Si piston alloy.