A novel method for observing the micro-morphology of keyhole wall during high-power fiber laser welding

Most of the laser welding defects are likely to be related to the welding process transport phenomena induced by the energy conversion process in the keyhole. The keyhole wall is the interaction interface between the laser and welded material, and studying its micro-morphology is significant for understanding the energy conversion process. Because the current measuring methods are limited, observation of keyhole wall micro-morphology is still a challenge. In this paper, a novel method was designed. The keyhole wall was preserved as the high-power fiber laser was suddenly shut off during welding process, and then it was measured by using a scanning electron microscopy (SEM). The results show that the laser beam directly acted on the keyhole front wall during welding. The concentric elliptical rings, wrinkles, and ripples were found on the laser-action region. These micromorphologies indicate that the energy coupling is mainly the absorption of the keyhole front wall, and the keyhole formation is similar to a laser drilling on the keyhole front wall during welding. The novel method can be used to investigate on the formation of the welding defects during high-power fiber laser welding in the future study. (C) 2015 Elsevier Ltd. All rights reserved.