Abstract
Aluminium alloy sheets with varying thicknesses have been intensively applied to thin-walled structures in the transportation industry. However, it is still a challenging work to assemble lightweight stacks with largely unequal thicknesses (i.e., A thick top sheet but a thin bottom sheet). In this research, a modified refill friction stir riveting (RFSR) technique was developed to connect AA7075-T6 aluminium alloy stacks with 3.2 mm top sheet and 1.0 mm bottom sheet. The joint geometric quality, microstructures, thermal softening state and tensile strength were experimentally investigated. The results reveal that the modified RFSR approach is capable of joining aluminium alloy stacks with largely unequal thicknesses. A reliable mechanical interlock was generated between the rivet and bottom sheet, benefiting from the drum-shaped buckling behaviour of the rivet shank in the modified RFSR process. Thanks to the high pressure in the rivet cavity and high rotation speed of top sheet material locked on the rivet shank, solid-state bonding with a high quality was always generated between the trapped top sheet and bottom sheet at varying feed rates. The feed rate demonstrated a strong controlling effect on the joint formation quality by altering the buckling degree of the rivet shank. Benefiting from the minor insertion depth of the rivet shank into the bottom sheet, the structural integrity of the thin bottom sheet was successfully retained. The maximum lap-shear force of studied joints was 4.78 kN with the feed rate of 1.0 mm/s, whilst the maximum cross-tension force was 1.49 kN with the feed rate of 4.0 mm/s.
Published Version
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