Achieving high strength and defect suppression in CFRP/aluminum alloy single-sided friction riveted joints via novel threaded rivets

In the single-sided joining of thermoset carbon fiber-reinforced polymer (CFRP) and aluminum alloy, the complete penetration of the workpieces is typically required, which can lead to challenges such as difficulty in drilling through stacked layers, damage to the joint, and potential safety concerns during service. This study employs the single-sided friction riveting (SSFR) process to achieve a reliable joining between CFRP and aluminum alloy, with an emphasis on elucidating the intrinsic differences in microstructural characteristics and mechanical properties of the joints induced by threaded structures of rivets. The external threaded rivet reduces heat generation, thereby inhibiting crack formation at the thread tips and expanding the process window for defect-free joints. A systematic comparative analysis of internal and external threaded rivets on joint mechanical performance was conducted, and the key load-bearing areas were identified. Cracks in defective joints prevent the aluminum alloy filled in the thread from effectively bearing the load during tensile-shear tests. The tensile-shear failure mode of internal threaded joints was primarily characterized by the plastic deformation of the load-bearing side aluminum alloy, leading to rivet pull-out, while external threaded joints failed mainly due to tearing of the load-bearing side aluminum alloy, causing rivet pull-out. The peak tensile-shear force of defect-free internal threaded joints is 7.0 kN, with a failure displacement of 6.4 mm, which is 6.1 % and 52.4 % higher than that of external threaded joints, respectively. This work demonstrates that optimizing the rivet thread design and process parameters can effectively improve the forming quality and enhance the mechanical performance of SSFR joints.