Numerical insight into heat transfer in surface melting and ablation subject to femtosecond laser processing aluminum

In the present work, the heat transfer in surface melting and ablation subject to femtosecond laser processing aluminum is investigated by a proposed algorithm concentrating on the energy consumed by latent heat of melting. The electron temperature-dependent material optical and thermophysical properties are employed in solving the two-temperature model (TTM). The evolutions of electron temperature and ion temperature pave a spatiotemporal way for evaluating the surface melting and ablation. The validation of proposed model is carried out by comparing the numerically calculated ablation depth with the experimentally measured ablation depth. The fraction of liquid by taking the latent heat of melting into account is put forward to describe the surface melting. A mushy zone characterizing the surface melting is identified. The electron-ion coupled heat transfer is found to trigger the rapid expansion of the mushy zone and melting depth in ultrafast surface melting. The energy consumed by latent heat of melting accounts for the delay of melting initiation moment and smaller melting depth, but it is inappreciable to ablation. Moreover, the energy loss through thermal radiation is numerically proved to have a neglectable impact on surface melting and ablation.