Fatigue crack growth characteristics in cast Al–Si–Mg alloys: Part I. Effect of processing conditions and microstructure

Fatigue strength and crack propagation behavior are critical attributes when designing structural components for high-integrity applications. Significant efforts have been directed in the past decade towards determining the effects of casting defects on fatigue response and many causal relationships are available in the literature. What has been missing, however, is a fundamental knowledge of the contribution of various constituent phases and features, specific to the alloy being considered, in governing fatigue crack initiation and propagation. In this work, model systems of Al-based cast alloys were investigated for fatigue crack growth under constant stress ratios using compact tension specimens. Grain size, secondary dendrite arm spacing (SDAS), modification, amount of Al–Si eutectic phase, α-Al phase, and other phases were controlled (kept constant/varied as needed to decouple effects) to determine their impact on fatigue crack growth. In addition, heat treatment effects and the influence of quenching residual stresses (macro-stresses) on fatigue crack growth have also been studied. The effects of critical casting parameters on the fatigue properties of cast Al components used for low-cycle fatigue as well as high-cycle fatigue applications will be critically reviewed and discussed.