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

This study investigates the influence of temporal laser modulation on the microstructure and mechanical properties of AlSi10Mg fabricated by laser powder bed fusion (L-PBF). Two modulation frequencies (5 and 50 kHz) and duty cycles ranging from 0.25 to 0.90 were examined using multiscale microstructural characterization, tensile testing, and thermal simulations. The response was found to depend strongly on the modulation frequency. Low-frequency PW processing (5 kHz) with duty cycles of 0.25–0.50 promotes inter-pulse solidification, leading to pronounced refinement of both grain and cellular microstructures compared with conventional continuous-wave (CW) processing. Thermal simulations predict cooling rates approaching 107 K s−1, consistent with the experimentally observed reduction in grain size and cellular spacing. The refined microstructure is accompanied by a weakened <001>//BD texture, the emergence of a <111>//BD texture component, and a slight increase in dislocation density, while the cellular chemical distribution remains essentially unchanged. However, the interrupted melting also promotes spatter generation and lack-of-fusion defects, leading to reduced ductility. In contrast, PW modulation at 50 kHz maintains a quasi-continuous melting regime, producing microstructures, crystallographic textures, and mechanical properties comparable to those obtained under CW processing, indicating that the shorter laser off-times are insufficient to significantly modify melt-pool solidification dynamics. Overall, these findings demonstrate that modulation frequency governs the transition between interrupted and quasi-continuous solidification, providing an effective strategy for tailoring the microstructure and strengthening mechanisms of LPBF AlSi10Mg, provided that process-induced defects are effectively controlled.