Thermocapillary convection and phase change in welding

Abstract

Purpose

In welding there is an intricate coupling between the composition of the material and the shape and depth of the weld pool. In certain materials, the weld pool may not penetrate the material easily, so that it is difficult or impossible to weld, while other seemingly quite similar materials may be well suited for welding. This is due to the convective heat transfer in the melt, where the flow is driven primarily by surface tension gradients. This paper aims to study how surface active agents affect the flow and thus the welding properties by surveying some recent 3D simulations of weld pools.

Design/methodology/approach

Some basic concepts in the modelling of flow in a weld pool are reviewed. The mathematical models for a convecting melt, with a detailed model for the surface tension and the Marangoni stress in the presence of surfactants, are presented. The effect of the sign of the Marangoni coefficient on the flow pattern, and thus, via melting and freezing, on the shape of the weld pool, is discussed.

Findings

It is seen that it is beneficial to have surfactants present at the pool surface, in order to have good penetration. Results from a refined surface tension model that accounts for non‐equilibrium redistribution of surfactants are presented. It is seen that the surfactant concentration is significantly modified by the fluid flow. Thereby, the effective surface tension and the Marangoni stresses are altered, and the redistribution of surfactants will affect the penetration depth of the weld pool.

Originality/value

The importance of surfactants for weld pool shapes, and in particular the convective redistribution of surfactants, is clarified.

Citation

Amberg, G. and Do‐Quang, M. (2008), "Thermocapillary convection and phase change in welding", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 18 No. 3/4, pp. 378-386. https://doi.org/10.1108/09615530810853637