Closure mechanisms in Al-Si-Mg cast alloys and long-crack to small-crack corrections

Crack growth behavior of small and long cracks has been a subject of much research; the differences observed in the growth response were largely attributed to crack closure. In this study, cast Al-Si-Mg alloys of various residual stress levels and Si content/morphology were investigated, and the dominant closure mechanisms were identified. The near-threshold fatigue crack growth behavior of the alloys is controlled by two types of closure: residual stress-induced (due to residual stresses introduced during heat treatment) and microstructure/roughness-induced (due to variations in Si content/morphology). These closure mechanisms were individually discussed and closure corrective techniques were applied to long crack growth results. The near-threshold closure corrected long crack growth data compare favorably with small crack growth data.