Room and high temperature fatigue behaviour of the A354 and C355 (Al-Si-Cu-Mg) alloys: Role of microstructure and heat treatment

The results of microstructural analyses and rotating bending fatigue tests highlighted that (i) SDAS influences room temperature fatigue behaviour of the peak-aged A354 and C355 alloys, while its effect on the overaged alloys at high temperature is negligible; (ii) fatigue cracks nucleated mostly from large intermetallic compounds; (iii) at room temperature, C355 alloy is characterized by higher fatigue strength (151 and 135 MPa for fine and coarse SDAS, respectively) in comparison to A354 alloy (133 and 113 MPa); after overaging and testing at high temperature, the behaviour of the two alloys is comparable. A good correlation between ultimate tensile strength and fatigue resistance was found, independent of microstructure and aging condition.