Tuning the microstructure and mechanical properties of AlSi10Mg powder bed fusion (PBF-LB) parts by local laser heat treatment

Abstract Laser powder bed fusion (PBF-LB) is increasingly adopted for producing complex aluminum components for lightweight aerospace and automotive applications. However, its broader application is limited by the relatively low fatigue strength of as-built parts. Adjusting the microstructure and mechanical properties of PBF-LB parts to increase their fatigue strength remains a key research focus. Most research concentrates on conventional heat treatment methods which affect the components microstructure globally and are time- and energy-expensive. In contrast, laser heat treatment (LHT) enables to locally tailor the microstructure and mechanical properties efficiently. Still, the potential of LHT for PBF-LB manufactured aluminum components and the underlying mechanisms remain largely unexplored. Therefore, this study investigates the microstructural evolution of PBF-LB manufactured AlSi10Mg parts subjected to a post-PBF-LB LHT. The influence of the key process parameters - laser power, relative movement speed of the laser beam on the part (feed rate), and beam diameter – on the microstructure and hardness – as well as the resulting mechanical properties are evaluated. Hardness, tensile strength, and fatigue performance are compared to the as-built and T6 heat-treated condition. The findings reveal that after LHT the microstructure closely resembles that of conventionally stress-relieved material. The controlled coarsening of silicon particles facilitates dislocation movement, allowing the tuning of hardness and ductility. LHT achieves tensile strengths comparable to T6 heat-treated specimens while offering increased ductility. In the low-cycle fatigue regime (< 1E5 load cycles) LHT specimens achieve the lowest fatigue strength due to the retained heterogenic scan track structure facilitating crack propagation. In the high-cycle fatigue regime (1E5-1E7 load cycles), LHT-treated samples demonstrate improved fatigue strength compared to the as-built condition and equal to T6 treatment owing to a superior defect tolerance. Overall, LHT provides an effective approach for localized microstructural adjustment and tuning of mechanical properties, representing a promising approach to achieve tailored part properties for PBF-LB manufactured parts.