Influence of the interlayer film thickness on the mechanical performance of AA2024-T3/CF-PPS hybrid joints produced by friction spot joining

Friction Spot Joining (FSpJ) is an innovative friction-based joining technique for metal-polymer hybrid structures. Friction spot joints of aluminium alloy 2024-T3 and carbon fibre-reinforced poly(phenylene sulphide) composite laminate (CF-PPS) were produced with an additional PPS film interlayer. Two different film thicknesses were investigated in this study: 100 and 500 μm. Lap shear testing demonstrated that the joints produced with 100-μm film (2093 ± 180 N) were stronger than the joints with 500 μm (708 ± 69 N). Additionally, the fracture surface analysis revealed a larger bonding area for the joints with 100-μm film (53 ± 2 mm²) as compared to the joints with 500-μm film (40 ± 1 mm²). Considering the low thermal conductivity of PPS, the thinnest film is more likely to soften by the frictional heat during the joining process. Hence, the low viscosity of the molten PPS favours the wettability of the parts’ surfaces. Microstructural analyses proved that the metallic nub formation and the interdiffusion of PPS chains between film and composite matrix are also favoured for thinner film use. Thus, superior adhesion between the partners is achieved. Therefore, it was concluded that the addition of the thinnest film interlayer leads to stronger joints.