High‐Cycle Fatigue Behavior and Damage Mechanism of Multiphase Al–Si Piston Alloy at Room and Elevated Temperatures

Microstructure evolution, tensile properties, fatigue crack initiation and propagation behaviors, and corresponding damage mechanisms of a multiphase cast Al–Si alloy used for pistons at room temperature (RT), 350 and 425 °C are investigated. The results show that tensile and fatigue strengths decrease with the increase of temperature. Casting defects such as pores and oxide films are the most preferential sites for fatigue initiation at all the temperatures. The preferential propagation path for fatigue crack is mainly through the Al matrix and second phases at room temperature, through Al matrix at 350 °C, and along grain boundary and phase/matrix interface at 425 °C. This may be attributed to the reduction of strengths of matrix and phase/matrix interface at elevated temperatures. Relationship between fatigue strength and defect size is also discussed using critical stress intensity factor and probability distribution of defect size.