Analysis of mechanical properties and microstructure of single and double-pass friction stir welded T-joints for aluminium stiffened panels
Douglas Wagner, Matteo Bernardi, Felix Grassel, Ting Chen, K. Schimanski, Luciano Bergmann, Benjamin Klusemann
Abstract
• Single-pass welds exhibit a lack of bonding which affects joint efficiency. • The lack of bonding characteristics are connected to the process parameters. • Double-pass welds eliminate the lack of bonding. • A second welding pass achieves 90% joint efficiency in skin direction. • A second welding pass achieves 95% joint efficiency in stiffener direction. This study investigates the application of Friction Stir Welding (FSW) for fabricating stiffened structures in AA2219-T31 using a T-lap configuration. These structures are vital in various applications where weight is a crucial factor, including aircraft fuselages, railway cars and automotive parts. This study assesses the formation dynamics of lack of bonding in single-pass welds, including the examination of microstructure, hardness, mechanical properties, and fracture locations. A second welding pass was employed over the initial weld to eliminate the lack of bonding. The implementation of a second welding pass significantly improves joint efficiency, achieving up to 90 % of the ultimate tensile strength in the skin direction and 95 % in the stiffener direction, establishing a new benchmark for AA2219-T31 T-joints. Additionally, no significant differences in grain size were found between single- and double-pass welds, highlighting the lack of bonding as key factor affecting the strength of the joints. The proposed method offers valuable insights for future industrial applications to avoid defects such as lack of bonding.