Low cycle fatigue response and fracture mechanism in a novel Al-3.5Si-0.5Mg-0.4Cu casting alloy

The LCF (low-cycle fatigue) behavior of a T6-treated low silicon cast aluminum alloy Al-3.5Si-0.5Mg-0.4Cu was investigated under axial symmetric tension-compression cyclic loading conditions. LCF behavior and results of experiment (under 6 different total strain amplitudes from 0.25 % to 0.5 %) are included. OM (Optical Microscopy), SEM (Scanning Electron Microscope), XRD (X-Ray Diffraction) and TEM (Transmission Electron Microscope) are employed to observe and analyze the fracture morphology and microstructure evolution. The results demonstrate that cracks were initiated from surface or subsurface defects. A higher total strain amplitude led to a smaller sum area of fatigue crack initiation region as well as a steady crack propagation regime, and a larger fatigue striation bandwidth. Furthermore, crack propagates along the interface between eutectic silicon and α-Al matrix under lower strain amplitudes. Otherwise, it extends through eutectic silicon particles if higher strain amplitudes are applied.