HYDROGEN ENRICHMENT IN LASER-BEAM WELDING OF ALUMINUM

A theoretical investigation of the hydrogen concentration distribution in an aluminium workpiece during welding is presented. The driving fo rce for hydrogen transport is thermal diffusion, whereby a diffusion c urrent is brought about by temperature gradients. The sign of the resp ective transport coefficient is negative for H in Al, which means that hydrogen will accumulate in the heated regions. An analytical solutio n is obtained under somewhat restrictive assumptions, which is complem ented by a numerical solution allowing for more realistic input. Both solutions agree qualitatively, yielding enrichment factors of two and more for the cases studied. It is predicted that higher processing spe eds will result in less enrichment. The significance of these results for the weld quality is discussed.