Ultrasonic vibration enhanced friction stir welding of titanium to aluminum

Abstract

Ti/Al hybrid structures offer advantages in lightweight design and cost reduction, but joining them is challenging due to differences in thermophysical properties. Friction stir welding (FSW) is a promising method but often leads to insufficient material flow and lack of penetration defects due to the need for low heat input to minimize intermetallic compounds (IMCs). To address these issues, ultrasonic vibration-enhanced friction stir welding (UVeFSW) was proposed for joining Ti/Al dissimilar materials in this study. The synergistic mechanism of ultrasonic vibration on the microstructure evolution and mechanical properties of Ti/Al dissimilar FSWed joints were systematically studied by multi-scale simulations and experiments. It shows that ultrasonic vibration promotes vertical material flow, reducing lack of penetration defects and enhancing mechanical properties. Transmission electron microscopy (TEM) analysis confirmed the formation of Al₁₈Ti₂Mg₃ and Al₃Ti at the interface, with molecular dynamics simulations indicating that Al₃Ti has higher interfacial strength. Ultrasonic vibration facilitates Ti diffusion, promoting the transformation of Al₁₈Ti₂Mg₃ into Al₃Ti and alleviating micro-stress concentration caused by excessive lattice mismatch. This highlights novel insights into the beneficial role of ultrasonic vibration in FSW process. UVeFSW addresses a critical challenge in Ti/Al FSW process by achieving an optimal balance between low heat input and adequate material flow, improving joint strength by 16.8 %, reaching 330.9 MPa. These results highlight the potential of UVeFSW for joining Ti/Al hybrid structures, offering valuable theoretical and practical insights for advanced engineering applications.