Friction Stir Spot Welding for CFRP/Al Using CFRP Laminated Composites with an Outermost Layer of Thermoplastic Resin

Abstract

Friction stir spot welding (FSSW) using thermoplastic resins as an adhesive, which uses the friction induced heat to melt them, has been developed as a method for welding Al alloys and Carbon Fiber Reinforced Plastics (CFRP). Since this method requires a process of inserting thermoplastic resins as an adhesive, efficient method for higher production cycle and higher interfacial strength between CFRP and the adhesive are expected to be developed. In this study, we have developed a proper laminated composite in which PA12 resin is laminated on the outermost layer of CF/Epoxy prepreg for the usage in FSSW. A co-curing laminate in which the PA12 resin in the outermost layer was melted before the curing of the epoxy resin, a co-curing laminate in which the PA12 resin was melted after the curing process, and a laminated composite in which PA12 resin was laminated by press molding as the next process after molding the CFRP were prepared, and their mechanical properties were evaluated by a three-point bending test. Their maximum flexural loads at fracture were the same as CFRP. Furthermore, FSSW of the prepared laminated composites and aluminum alloy was performed and their welded strength was evaluated by a tensile shear test. The shear strength of 12.1 ± 0.6 kN, which was higher than that of FSSW when the thermoplastic resin was inserted between the Al alloy and CFRP, was obtained for the specimen using the laminated composite in which the PA12 resin in the outermost layer was melted before the curing of the epoxy resin in co-curing process.