In situ X-ray phase contrast imaging of the melt and vapor capillary behavior during the welding regime transition on aluminum with limited material thickness

The X-ray phase contrast imaging is a powerful method to understand the fundamental behavior of the melt and keyhole during the laser beam welding process. In this paper, the keyhole-induced vapor capillary formation in the melt pool is investigated by using an adjustable laser beam source. For this purpose, the aluminum A1050 specimen with a thickness of 0.5 mm is molten only with the heat conduction welding regime by using the ring-mode laser beam. Once the specimen is molten through, the core multi-mode laser beam is then applied to vaporize the melt and a transition to keyhole welding regime occurs. Therefore, the core multi-mode laser beam with an intensity value of 33.3 MW/cm2 is investigated. The correlation between the keyhole-induced vapor capillary and the melt behavior is further investigated in this paper which was recorded with a high sampling rate of 19 kHz. In addition, a theoretical calculation about the keyhole depth is discussed in this paper.