Comparison Between Isothermal and Non-Isothermal Fatigue Behavior in a Cast Aluminum-Silicon-Magnesium Alloy

Abstract

In the present study, the out-of-phase thermomechanical fatigue (OP-TMF) behavior of a cast aluminum-silicon-magnesium alloy, the A356.0 alloy which has been widely used in diesel engine cylinder heads, is compared to room-temperature and high-temperature low cycle fatigue (RT-, HT-LCF) behaviors. For this purpose, strain/temperature-controlled isothermal and non-isothermal fatigue tests were performed based on realistic loading conditions in cylinder heads. Fatigue tests results showed that the plastic strain increased during cycles under constant mechanical strain amplitude, while the specimen failed. Under LCF loadings, the cyclic hardening occurred at low temperatures for the A356.0 alloy and the cyclic softening occurred at high temperatures, as it was also observed in TMF tests. The radial and longitudinal temperature gradients during TMF tests were almost 2 and 3°C, respectively. Comparing stress-strain hysteresis loops, tensile stresses at minimum temperatures under TMF loadings were more than tensile stresses at LCF cases, due to the out-of-phase loading condition in TMF tests. In this state, maximum temperatures occurred within compressive regimes and minimum temperatures occurred at tensile loads. In general, TMF lifetimes were less than LCF ones due to severe conditions and the temperature deviation in TMF tests.