<p>During laser welding of Al-Si coated press-hardened steel, Al readily diffuses into the molten pool, negatively affecting weld quality. However, the transport behavior of Al remains insufficiently understood. A new model was established to simulate full-penetration laser welding of Al-Si coated press-hardened steel in this study. The melting and flow of Al-Si coating were systematically analyzed, and the formation mechanism of Al segregation was clarified under different welding speeds (2 and 6&#xa0;m/min). Simulation results revealed that molten pool flow was primarily governed by Marangoni circulation, with a particularly strong vortex observed near the keyhole region. Marangoni circulation transported the molten Al-Si coating from the keyhole region into the molten pool. As the Al migrated toward the rear of the pool, decreased flow velocity combined with rapid solidification resulted in Al segregation. At 2&#xa0;m/min, the strong Marangoni circulation and slow solidification improved the flow and dilution of Al element. When the welding speed was increased to 6&#xa0;m/min, The Marangoni circulation weakened, and the molten pool flow velocity decreased because of the reduced heat input and accelerated solidification. Additionally, the flow velocity at the fusion line was significantly lower than that at the weld center, resulting in obvious Al segregation at the fusion line. The simulation results agree well with experimental observations, offering key insights into Al flow and segregation mechanisms.</p> Graphical Abstract <p></p>