Fatigue resistance of selectively laser melted aluminum alloy under T6 heat treatment

Due to complex microstructure and defect inherited from this ALM process, it is necessary to assess the fatigue resistance of the material constitutive of manufactured parts prior to certification. This work is precisely tackling this issue with a special attention paid to the role of microstructural parameters and defects on fatigue life. Specimens were built with two configurations (0° and 90°) in order to evaluate the impact of the induced anisotropy of microstructure on fatigue properties. X-Ray 3D tomography was used to characterize defect population by their size. Microstructure is furthermore characterized by considering four characteristic scales [1-3]: melt-pools, crystallographic grains, dendritic structure and the precipitates. The fatigue properties are determined by establishing S-N curves for as-built and heat-treated samples for R= -1. The defect size responsible for the fatigue damage initiation is determined in each sample so as to establish a relation between the fatigue limit and the defect size by means of Kitagawa type diagrams. It is shown that the defect size is the first order parameter in terms of the fatigue resistance. Through the Kitagawa diagrams for as-built and heat treated samples, we quantify the improvement of the fatigue resistance due to the peak hardening treatment.