Friction stir spot welding of 5052 aluminum alloy to carbon fiber reinforced polyether ether ketone composites

The hybrid structure composed of aluminum alloy and carbon fiber reinforced plastics could combine their advantages. In order to investigate the weldability of these two lightweight materials, the hybrid joints of 5052 aluminum alloy (AA5052) and carbon fiber reinforced polyether ether ketone composites (CF-PEEK) were fabricated by friction stir spot welding. The variance analysis revealed that the dwell time and plunge speed were the most significant factors. By optimizing the welding parameters, the ultimate tensile shear load reached 2690±64 N (the dwell time: 8 s, the plunge speed: 10 mm/min). The interface could be divided into pin-affected zone, shoulder-affected zone, resin adhesive zone and resin concentrated zone. Since resin concentrated zone could not provide interfacial bonding due to delamination, the shoulder-affected zone and pin-affected zone were decisive regions for mechanical properties. The bonding mechanism included three parts: adhesive bonding provided by re-solidified resin, macro-mechanical interlocking of aluminum alloy that entered CF-PEEK, and micro-mechanical interlocking of resin that was tightly trapped at surface slits as well as the carbon fibers beset into AA5052. This work clarifies the interfacial characteristics of AA5052/CF-PEEK hybrid joints and provides an approach to improve the mechanical properties.