Effect of zinc vapor forces on spattering in partial penetration laser welding of zinc-coated steels

• Published in: Journal of materials processing technology 2021-12, Vol.298, p.117282, Article 117282
• Main Authors: Hao, Yu, Chen, Nannan, Wang, Hui-Ping, Carlson, Blair E., Lu, Fenggui
• Format: Article
• Language: English
• Subjects: Drag; Fluid flow; High speed cameras; Laser beam welding; Laser welding; Mathematical models; Numerical models; Penetration; Spattering mechanism; Steel; Three dimensional models; Vapors; X ray imagery; Zinc; Zinc coatings; Zinc vapor force; Zinc-coated steel
• ISSN: 0924-0136; 1873-4774
• DOI: 10.1016/j.jmatprotec.2021.117282

A three-dimensional thermal-fluid numerical model considering zinc vapor interaction with the molten pool was developed to study the occurrence of zinc vapor-induced spatter in partial penetration laser overlap welding of zinc-coated steels. The zinc vapor effect was represented by two forces: a jet pressure force acting on the keyhole rear wall as the vapor bursts into the keyhole and a drag force on the upper keyhole wall as the vapor escapes upwards. The numerical model was calibrated by comparing the predicted keyhole shape with the keyhole shape observed by high-speed X-ray imaging and applied for various weld schedules. The study showed that large jet pressure forces induced violent fluctuations of the keyhole rear wall, resulting in an unstable keyhole and turbulent melt flow. A large drag force pushed the melt adjacent to the keyhole surface upward and accelerated the movement of the melt whose velocities reached 1 m/s or even higher, potentially inducing spatter. Increased heat input facilitated the occurrence of large droplets of spatter, which agreed with experimental observations captured by high-speed camera.