Effect of low-temperature stress relieving heat treatments on fatigue behaviour and failure mechanisms of L-PBF AlSi10Mg aluminium alloy
Rui F. Fernandes, J.S. Jesus, Ricardo Branco, L.P. Borrego, J.D. Costa, J.A.M. Ferreira
Abstract
• Tailored heat treatments maintained Al-Si network; • Heat treatments enhanced ductility, reduce hardness and tensile strength; • Heat treatments improved low-cycle fatigue strength; • Mixed ductile–brittle fracture modes were identified. While the fatigue behaviour and failure mechanisms of additively-manufactured AlSi10Mg aluminium alloy subjected to post-processing heat treatments carried out at temperatures near the second exothermic peak (320 °C) has been already explored, studies on temperatures slightly below the first exothermic peak (260 °C) are still lacking. This paper addresses the effect of these low-temperature post-processing heat treatments on fatigue behaviour and failure mechanisms of AlSi10Mg aluminium alloy manufactured via powder bed fusion. Four material conditions were investigated: as-built, stress relief at 300 °C for 2 h, stress relief at 250 °C for 2 h, and hot isostatic pressing at 250 °C for 2 h under 100 MPa. Fatigue tests were conducted under strain-controlled conditions (R ε = -1) with strain amplitudes ranging from 0.1 to 1.5 %. Failure mechanisms, microstructure, hardness, ductility, and tensile strength were also evaluated. The results showed that microstructural changes induced by the heat treatments enhanced ductility, and reduced hardness, tensile strength and fatigue scatter. Heat treatments improved the low-cycle fatigue performance but were relatively ineffective in the high-cycle fatigue regime. Fatigue crack initiation was linked to manufacturing-related defects located near the surface or subsurface while failure mechanisms exhibited both brittle and ductile characteristics with a predominance of brittle modes.