The modeling of keyhole digging during ablative laser beam interaction with aluminum/magnesium joint
A lateral observation of laser-induced keyhole through the quartz window is an easy and cheap experimental method. It opens an interesting perspective for the study of keyhole asymmetry in case of dissimilar metal combinations. To quantify the effect of quartz window on the observed phenomena and to predict the keyhole shapes observed in aluminum/magnesium interface, a simplified 2D model of thermal ablation was developed. The main numerical achievement of this work consists in the simulation of keyhole with high depth to width ratio thanks to the adaptive mesh stiffening used in deformed geometry formulation. The model was able to correctly reproduce the keyhole dimensions in case of homogenous and binary metal/quartz combinations and allowed estimating the effect of quartz on the keyhole depth. In case of aluminum/magnesium metal combination, the model renders the keyhole evolution with laser offset from the joint line that would take place in absence of quartz window. In case of the beam centered on the joint line, the mismatch in vaporization temperatures induced the preferential formation of deep and thin keyhole on magnesium side. The displacement of the keyhole on magnesium induced further slight increase of penetration, when the displacement on aluminum reduced abruptly the keyhole.
