Thermal diffusion in laser beam welding of metals

Abstract

A theoretical investigation of the temperature and hydrogen concentration as a function of space in an aluminium workpiece during laser beam welding is reported. The driving force for hydrogen transport is thermal diffusion. The diffusion current is brought about by a temperature gradient. The sign of the respective transport coefficient is negative for H in Al, which implies that hydrogen will accumulate in the heated regions. Analytical solutions are obtained for the temperature and concentration fields which comprise convective and conductive heat transfer, and hydrogen transport by convection, diffusion and thermal diffusion. The spatial characteristics are discussed in detail using various approximations for the upstream and the downstream region as well as for the region close to the keyhole.