Hajime Ikuno

Thermo-mechanical Fatigue Behavior of Al-Si-Cu-Mg Casting Alloy

This paper describes the thermo-mechanical fatigue behavior of Al-Si-Cu-Mg casting alloy. The alloy is widely used for cylinder heads and pistons of automobile engines. Repeated cycling between driving and resting, or low-power and high-power driving cause thermal cycling in the engine materials. The thermo-mechanical fatigue property is therefore very important to develop high-performance engines. This study aims to characterize the cyclic stress-strain behavior of this alloy and to clarify the factors dominating the fracture life. Results obtained are : (1) The stress-strain behavior changes remarkably during thermal cycling. Cyclic hardening and cycling softening occur in the higher and lower strain ranges, respectively. (2) A thermo-mechanical fatigue fracture limit diagram is obtained by connecting fracture points on the inelastic strain range - number of cycles relationship. (3) Consequently, in 10 3 - 10 4 cycles, it is considered that poor ductility and inelastic strain increase due to overaging dominate the thermo-mechanical fatigue life of the alloy.