Study on mechanical properties and microstructure of CFRTP cutting fluid assisted stir friction welding joints

Abstract The bonding technology of carbon fiber‐reinforced thermoplastics has attracted much attention in industrial fields such as airfoils and car bodies. Cutting fluid‐assisted stir friction welding is a potential method for reducing machining defects and enhancing the tensile properties of welds. In this paper, cutting fluid‐assisted friction stir welding is implemented to bond carbon fiber‐reinforced polyetherimide (CF‐PEI) plates. The welds are evaluated by surface morphology, area calculation of the OM image, SEM of the fracture, carbon fiber state, and tensile analysis. From the weld surface morphology and OM images, the weld surface quality is improved, the material loss is reduced, and the weld bonding area is increased by cutting fluid assistance, which provides an environment for the movement of carbon fibers. The microanalysis results show that cutting fluid assistance helps in the interweaving of carbon fibers, and the process parameters affect the interweaving behavior of carbon fibers. The fusion interface is enhanced due to the mechanical interlocking of the carbon fibers. The maximum tensile strength reaches 32.5Mpa, equivalent to 77% of the base material, which increases by 49.4% compared with the conventional FSW. Highlights Cutting fluid‐assisted friction stir welding technology is applied to the welding of carbon‐fiber‐reinforced thermoplastic. The zones of the weld are delineated by the state of the carbon fiber and the characteristics of each zone are analyzed. Cutting fluid assisted technology reduces weld material loss and enhances the mixing of carbon fiber and base material. Summarize the weld enhancement mechanism by analyzing the carbon fiber microstates.