Mechanism of keyhole evolution and welding quality of electron beam welded magnesium alloy with scanning path variation via modeling and numerical study

• Main Authors: Yin, Qianxing, Yang, Ziyou, Li, Hui, Du, Hejun
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Article
• Language: English
• Published: 2024
• Subjects: Engineering; Scanning path; Fluid flow
• Online Access: https://hdl.handle.net/10356/181319
• Institution: Nanyang Technological University

Welding quality of electron beam welded joint is usually susceptible to the stability of keyhole during welding process. The more stable the keyhole, the better the welding quality. To reveal the evolution mechanism of keyhole and welding quality of the electron beam welded joint of magnesium-gadolinium alloy under different scanning path, numerical simulation was conducted for the changes in morphology of keyhole and liquid flow in molten pool. The magnesium-gadolinium alloy was welded by electron beam in vacuum with two different scanning paths, sinusoid path and cochleoid path, indicating the identical heat input, welding speed, and focusing state. The stability of keyhole was mainly related to the frequency of keyhole collapse. When the sinusoid scanning path was adopted, the fluids both inside the molten pool and at keyhole wall were disorder, corresponding to the numerous independent vortices and dramatically chaotic flows at their junctions. The maximum velocity of fluids ranged from 0.79 m/s to 1.02 m/s. The average and maximum depth of keyhole were 3.48 mm and 4.51 mm, respectively, meaning that the keyhole collapsed frequently. As the scanning path was changed into cochleoid mode, the electron beam scanned in a homogeneous manner without abrupt change in direction and speed like sinusoid path at its peaks and troughs. The maximum velocity of fluids was more uniform without drastic variation, ranging from 0.90 m/s to 1.01 m/s. The average and maximum depth of keyhole were decreased to 3.30 mm and 4.05 mm, respectively, indicating the more stable keyhole and alleviated collapse. Both the actual in-situ capture of molten pool signature and porosity inside the weld corresponded to the analysis of the change in keyhole stability.