Revealing optimal melting regimes for defect lean single-track aluminium laser powder bed fusion builds

AlSi10Mg is a typical alloy used in additively manufactured components such as heat exchangers with thin-wall features. However, printing of single-track thin walls remains a challenge owing to inherent process instabilities. Here, we use in situ synchrotron X-ray imaging to develop a process map identifying five distinct melting regimes with their characteristic defect formation tendencies. Quantification of melt pool shape, void formation and melting efficiency, point to an optimal, defect-lean keyhole regime for single track builds with a high melting efficiency of 25% and an energy reduction of ~30% from the commonly used conduction regime. The unstable keyhole region was found to be larger than that reported for other alloys, e.g. Ti-6Al-4V. We also reveal a transitional keyhole flickering phenomenon, causing irregular tracks due to rapid (~1 ms) switching between keyhole and conduction modes, which is explained with the aid numerical simulation and correlated with melt pool size, physical properties and the dimensionless Strouhal number. Process mapping enhances our understanding of processing strategies for thin-wall builds, informing robust, high-quality additive manufacturing methods.