On the structural integrity of hypereutectic Al-Si alloy processed by laser-based powder-bed fusion

Hypereutectic Al-Si alloys possess good mechanical and functional properties, e.g., a comparably low coefficient of thermal expansion (CTE). Due to their utilization in safety-critical applications such as metal mirrors for space applications, examination of the mechanical response under complex loading scenarios is pivotal. Therefore, the present study presents first systematic results on the fatigue behavior of an Al-basis alloy with a Silicon concentration of approximately 40 wt.% processed by laser-based powder-bed fusion (PBF-LB/M). Monotonic tensile properties as well as fatigue behavior in the high-cycle (HCF) and low-cycle fatigue (LCF) regimes were assessed and compared with a melt-spun and extruded benchmark condition. To evaluate anisotropy, specimens were extracted parallel and perpendicular to the building or extrusion direction, respectively. Microstructural characterization and computed tomography were employed to correlate microstructure, inherent porosity and mechanical properties. The PBF-LB/M condition exhibits a pronounced increase in performance, reaching ultimate tensile strengths of up to ∼360 MPa compared to ∼220 MPa for the conventionally processed material. In the HCF regime, additively manufactured specimens show superior fatigue performance, with fatigue limits of up to ∼130 MPa. However, fatigue behavior is strongly affected by inherent defects, and a reduced resistance to fatigue crack propagation is observed under LCF loading. CTE investigations reveal only minor anisotropy and comparable values for PBF-LB/M conditions and conventional counterparts. In summary, the results demonstrate that PBF-LB/M processing enables a favorable combination of high-strength, enhanced high-cycle fatigue performance and low thermal expansion in hypereutectic Al-Si alloys, while highlighting the decisive role of process-induced defects. • Fatigue behavior of additively and conventionally hypereutectic Al-Si is examined. • HCF and LCF regimes were considered. • Fatigue behavior for all conditions is governed by inherent pores and defects. • Metallographic and radiographic testing reveal anisotropic fatigue properties. • Isotropic CTEs for both conditions are determined.