Effect of non-equilibrium solid state phase transformation on welding temperature field during keyhole mode laser welding of Ti6Al4V alloy

The effect of non-equilibrium solid state phase transformation on numerical simulation of welding temperature field is researched during keyhole mode laser welding of Ti6Al4V alloy. The simulation of the welding temperature field considering equilibrium phase transformation is obtained by means of the model of the heat transfer and fluid flow after the keyhole presetting. Based on the simulation considering equilibrium phase transformation, the simulation considering non-equilibrium phase transformation is modified, in terms of partitioning the regions and endowing the physical parameters considering non-equilibrium phase transformation. Compared with those considering equilibrium phase transformation in the horizontal planes, the temperature contours greater than or equal to 1300 K considering non-equilibrium phase transformation are elongated, while the temperature contours between 1100 K and 1300 K considering non-equilibrium phase transformation are shortened. The difference of the welding temperature fields considering equilibrium and non-equilibrium phase transformations basically emerges in the cooling stage. The temperature fields considering non-equilibrium phase transformation after modifying once and twice are almost the same, signifying that the simulation considering non-equilibrium phase transformation after modifying once is sufficient. The computational results considering non-equilibrium phase transformation agree well with the experimental ones in contrast with those considering equilibrium phase transformation, showing that the simulation considering non-equilibrium phase transformation after modifying once is reliable and satisfactory.