Effects of welding parameters and thermal insulation on the mechanical behavior and microstructure of friction lap-welded aluminum to glass fiber–reinforced thermoset composite with a thermoplastic PA6 interlayer

Friction lap welding was used to join aluminum with glass fiber–reinforced thermoset polymer (GFRP) using a thermoplastic interlayer. The effect of different welding parameters on joint strength and fracture surfaces was investigated, and the optimal welding parameters were determined using the Taguchi method. Results revealed that low heat generation led to weak mechanical interlocking between GFRP and the thermoplastic interlayer, while high heat generation caused degradation of the aluminum/thermoplastic polymer interface. The tool traverse speed was found to be the most influential parameter in terms of joint strength, followed by plunge depth and rotational speed. Moreover, thermal measurements were conducted during the welding process using thermocouples. An uneven thermal distribution was discovered across the overlap area due to dissimilar substrates. This issue was resolved by incorporating aluminum thermal insulation, resulting in improved heat distribution and a significant enhancement of 94% in joint strength. Scanning electron microscopy (SEM) was employed to identify joining mechanisms and examine the effect of welding parameters on joint microstructure. Furthermore, Fourier-transform infrared spectroscopy (FTIR) was used to investigate chemical bond formation at the aluminum/thermoplastic polymer interface. The results showed that the joining mechanisms involved mechanical interlocking between the thermoplastic interlayer and aluminum, as well as chemical bonding, penetration, and intertwining between the thermoplastic interlayer and the thermoset composite.