High Temperature Fatigue Behavior of Eutectic Al-Si-Alloys Used for Piston Production

Pistons of IC engines are typically subjected during operation to high cycle fatigue loading cycles at high temperatures (up to 350 °C) in areas facing the combustion chamber. During operation the high temperature exposure results in a progressive loss of fatigue strength of the material at the weakest areas of the piston and may eventually results in a premature failure by crack initiation and propagation. The quantification of the temperature effect on fatigue strength inevitably require experimentation since such data are scarce. An extensive fatigue testing program of eutectic Al-Si alloys at room temperature and at several high temperatures (250 °C, 300 °C and 350 °C) is reported. Specimens were extracted from piston crowns and tested in a rotating bending test machine. The resulting fatigue strength loss at 107 cycles is quantified by a staircase approach. The influence of the test temperature is investigated in terms of chemical composition, process route and of mechanisms of fracture observed in the broken specimens.