Abstract : The growing demand for lightweight hybrid structures has intensified research on joining aluminium with polymers and fibre-reinforced thermoplastic composites, particularly for applications in the transport sector. However, the large physical, chemical and thermal differences between these materials hinder the use of conventional joining techniques. The objective of this study is to provide a critical and comprehensive review of aluminium–polymer and aluminium–composite joining based on friction stir welding (FSW) technologies, with emphasis on joint configuration, material positioning and tool design. The analysed literature is systematically classified according to friction stir butt welding (FSBW) and friction stir lap welding (FSLW) approaches. The review demonstrates that FSBW generally results in low joint efficiencies, poor surface quality and frequent internal defects, and no relevant studies addressing metal–composite joining by this technique were identified. In contrast, FSLW exhibits significantly higher potential, particularly when the aluminium plate is positioned on top of the polymeric material. The use of short-pin or pinless tools is shown to be especially effective, as it limits polymer degradation, reduces tool wear and preserves fibre integrity in reinforced composites. Even so, surface pretreatments and interlayer strategies are identified as key factors for further enhancing joint strength and reliability. In sum, is should be stated that FSLW with aluminium on top represents the most robust and versatile strategy for joining aluminium to polymers and fibre-reinforced thermoplastic composites.
Pereira et al. (2026) studied this question.