On the low-cycle fatigue behavior of friction stir welded Al-Si12 parts produced by selective laser melting

The solid-state friction stir welding (FSW) process was used to join Al-Si12 parts fabricated via the selective laser melting (SLM) technique. The effect of the welding process on microstructural evolution and mechanical properties of the samples is investigated in present work. Microstructural studies demonstrate that FSW is capable of changing Si phase morphologies (i.e. shape and size) resulting in various mechanical properties. The stir zone of the welded joint shows significantly lower micro-hardness in comparison to the as-built SLM samples. Correspondingly, the friction stir welding process results in significant reduction of tensile strength, while ductility is strongly improved. The fully-reversed strain-controlled low-cycle fatigue (LCF) tests imply that at low strain amplitudes the FSW and SLM samples show almost the same fatigue life, while at the high strain amplitudes the SLM samples show superior LCF performance. Fracture analysis of fatigued samples reveals that the near-surface pores lead to the crack initiation in both SLM and FSW cases.