<title>Thermocapillary convection in a melted pool during laser surface remelting</title>

Abstract

The melted pools produced during some laser material processing (welding, surface treatment, etc.) are subjected to high convective motions which very significantly affect the thermal coupling between the laser beam and the working piece. This flow is produced by the surface tension gradient which results from the non-uniform temperature distribution at the free surface of the material. This physical phenomenon is known as the Marangoni or thermocapillary convection. The thermocapillary convection induces a strong mixing effect which reduces the gradients of any quantity transported in the melted material (such as temperature, composition, etc.). The shape factor of the melted pool, and therefore the free surface stability, are greatly modified by these convective motions. For some experimental conditions, distortions of the free surface could exist after resolidification, producing a rough state of the surface. We present in this paper a numerical simulation of thermocapillary convection in a melted pool produced by a stationary heat flux on a rectangular target (the resolution is limited to the 2-D problem). After a short presentation of the physical and mathematical model, the temperature fields and the streamlines obtained for various physical conditions are analyzed.