Influence of laser pulse frequency and duty cycle on the microstructure and mechanical properties of L-PBF AlSi10Mg

This study investigates the effect of temporal laser modulation on the microstructure and mechanical properties of AlSi10Mg fabricated by laser powder bed fusion (L-PBF). Two pulsed-wave (PW) frequencies (5 kHz and 50 kHz) and a broad range of duty cycles (0.25–0.90) were applied to assess the influence of laser pulse modulation on solidification behaviour and resulting material performance. We show that, at 5 kHz and low duty cycles (0.25–0.50), PW processing produces a pronounced refinement of both grain structure and cellular–dendritic features relative to continuous-wave (CW) irradiation. This refinement is attributed to inter-pulse solidification and ultra-high cooling rates approaching 107 K.s-1 in PW regime, accompanied by a modest increase in dislocation density within aluminum cells, as revealed by TEM analysis, and a reduction in <001>//BD texture intensity. These microstructural modifications enhance the yield strength, but the formation of spatters, likely linked to pulse overshoot, and the resulting lack-of-fusion defects affect ductility. In contrast, increasing the modulation frequency to 50 kHz produces microstructures and mechanical properties comparable to those obtained under CW irradiation, indicating that the reduced pulse duration is insufficient to significantly modify melt-pool solidification. This behavior contrasts with the vibration-induced refinements reported for alloys such as 316L and In625 at similar high frequencies, underscoring the alloy-specific sensitivity of AlSi10Mg to temporal laser modulation. Overall, low-frequency pulsed laser modulation is shown to be a powerful strategy for tailoring the microstructure and strengthening response of L-PBF AlSi10Mg, while elucidating the process-induced defect mechanisms that ultimately control the strength–ductility trade-off.