New insights on the pulsed wave L-PBF process. application to an AlSi10Mg aluminium alloy

We investigate the potential of pulsed-wave (PW) laser irradiation for processing AlSi10Mg alloy in an open-architecture laser powder bed fusion (L-PBF) set-up. Two PW frequencies (F = 5 kHz and F = 50 kHz) were compared with conventional continuous-wave (CW) processing. First, single-track experiments conducted on a pre-built substrate established stability windows for each mode, revealing narrower processing windows in PW regime, shifted towards higher scan speeds. During 3D builds, high-speed imaging and surface characterisation revealed that PW irradiation, particularly at 5 kHz, induced increased spatter and oscillatory melt pool behaviour, reflecting a less stable fusion regime. This led to an inferior surface finish and a reduced density of 97.5%, compared to approximately 99.5% under CW conditions. However, increasing the duty cycle to 80% restored density to nearly 99%, while maintaining the enhanced dimensional precision associated with PW irradiation. To elucidate the underlying heat-transfer transient behaviour, a numerical thermal model was developed and validated across various power levels, speeds, frequencies, and duty cycles. Numerical calculations, combined with analytical thresholds, enable the optimisation of the PW regime across all (F, dc) conditions and material properties. Overall, despite narrower process windows and increased melt-pool instability, PW irradiation enables the fabrication of nearly fully dense AlSi10Mg parts while offering improved heat-input control and dimensional accuracy, highlighting its potential as a viable strategy for process optimisation in L-PBF.