Thermo-mechanical fatigue behavior of cast 319 aluminum alloys

Stress-strain behavior and durability of cast 319 aluminum-copper alloys are studied at high temperatures and under thermo-mechanical fatigue (TMF), exposing rate sensitivity and microstructural changes. The decrease in strength during cycling was attributed to the significant coarsening of the precipitates at high temperatures, which was confirmed with transmission electron microscopy. The results show that the stress-strain response is similar under out-of-phase (OP) and in-phase (IP) thermo-mechanical fatigue. However, TMF-IP fatigue lives are substantially lower compared to TMF-OP lives, which are very close to the isothermal low cycle fatigue (LCF) life obtained at a similar inelastic strain range. In fact, it is observed that TMF IP loading induces significant creep damage, while transgranular fracture predominates in all other testing conditions.