Transient fatigue crack growth behaviour of additively manufactured AlSi10Mg aluminium alloy under various post-processing treatments

This study investigates the transient fatigue crack growth (FCG) behaviour of AlSi10Mg aluminium alloy specimens produced by laser powder bed fusion and subjected to different post-processing treatments, including as-built, as-built shot-peened, stress-relieved, and stress-relieved shot-peened conditions. FCG tests were performed under constant amplitude (R = 0.05) and single tensile overload conditions, with overload ratios of 1.5, 2.0, and 2.5 applied at stress intensity factor ranges of 4, 7, and 9 MPa√m. Shot peening had minimal influence on near-threshold FCG rates in as-built specimens, though it slightly increased the threshold value. At higher ΔK values, as-built and as-built shot-peened specimens exhibited similar FCG behaviour, while shot peening provide no additional FCG resistance in stress-relieved specimens. Overload-induced crack closure was strongly influenced by the magnitude of the overload ratio, with as-built specimens showing FCG retardation even under lower overload ratios (OLR = 1.5). In contrast, stress-relieved specimens exhibited minimal sensitivity to such conditions. Higher overload ratios (OLR = 2.0 and 2.5) induced greater crack wake plasticity, resulting in pronounced crack retardation in both as-built and stress-relieved conditions. However, as-built specimens fractured under higher overload magnitudes, highlighting the superior ductility and toughness of stress-relieved specimens. Fracture surface analysis revealed plastic deformation mechanisms induced by overloads, confirming an enhanced crack closure after overload application.