Refill Friction Stir Spot Welding of Dissimilar AA6014 Al Alloy and Carbon-Fiber-Reinforced Polymer Composite

Both Al and carbon-fiber-reinforced polymer (CFRP) are being investigated as lightweight materials for automobile applications. To form effective hybrid materials from Al and CFRP, strong bonding between these two dissimilar materials is critical. Here, we analyzed the microstructure and tensile shear strength of joints between an Al alloy (AA 6014) and CFRP fabricated using refill friction stir spot welding (RFSSW). A maximum tensile shear load of 1.6 kN was measured for untreated AA 6014/CFRP specimens. Microscopy images of the Al-CFRP joints exhibited tight bonding along the joint interface without any noticeable defects. Moreover, Al-O-C, C-C, and C=O chemical bonds were detected on the tensile-shear fracture surfaces of both the Al alloy and CFRP sheets using X-ray photoelectron spectroscopy. Micro-mechanical interlocking and chemical bond formation were the key factors contributing to the tensile shear strength of the RFSSW joint. This study demonstrated that the RFSSW technique is a suitable bonding method for manufacturing metal-polymer hybrid structures.