Ultrafast laser micro-texturing of joining surface combined with ultrasonic vibration-assisted friction stir joining to fabricate Zr-based metallic glass parts

This study aims to fabricate Zr-based metallic glass (MG) parts directly through friction stir joining (FSJ) by addressing the poor machinability of Zr-based MGs. The joining mechanism, mechanical properties, and microstructure of FSJ joints were investigated to achieve high-strength joints. The result identified uneven temperature distribution at the joint interface as a critical factor for inadequate plastic deformation or viscous flow, affecting the joint strength. Therefore, a new strategy is proposed to regulate the interface temperature and material plastic deformation during Zr-based MG joining via ultrafast laser micro-texturing of the joining surface combined with ultrasonic vibration-assisted friction stir joining (UL-UVaFSJ). The results show that ultrasonic vibrations enhance longitudinal friction and energy transfer, promoting uniform temperature distribution with improved viscous flow. Additionally, ultrafast laser-fabricated micro-textures alter heat generation, reducing temperature unevenness at the source. These factors collectively yield a uniform temperature distribution at the joint interface, crucial for reliable joining. The factors also maintain the even plastic flow of Zr-based MGs in the supercooled liquid region (SCLR) for a critical duration, essential for successful joining. Transmission electron microscopy reveals true metallurgical joining with the proposed method. The joining strength of Zr-based MGs is 1.37 GPa, reaching 91.3 % of the as-cast material and enabling the successful fabrication of a high-strength, crystallization-free MG gear shaft. The findings are pivotal for large-scale MG part fabrication and will significantly promote their industrial application.