Structural behaviour of Metal–Composite joints produced by friction stir spot welding

In this study, the joining of AA6082–T6 to glass fibre reinforced polyamide 6 by friction stir spot welding was investigated. The study encompassed the comparison of two surface pretreatments, the conventional grinding and the mechanical grooving pretreatments. The morphological analysis demonstrated that, depending on the surface pretreatment, the metal–composite interaction at the interface presented markedly different characteristics, resulting in the creation of different joining mechanisms. In addition, the joining mechanisms observed at the shoulder actuation zone (SAZ) are significantly different from the mechanisms found outside this region. Inside the SAZ, welds produced with conventional grinding showed aluminium-fibre micro–mechanical interlocking, and outside the SAZ, the joining was promoted by aluminium-polymer micro–mechanical interlocking. In contrast, welds produced with mechanical grooving exhibited aluminium-fibres meso–mechanical interlocking, which are better established inside the SAZ, and are influenced by the fibre orientation. Furthermore, by using mechanical grooving, a larger tool and a slower plunge rate, welds with a tensile–shear force of 11547 ± 317 (N) were obtained, with the failure of the aluminium plate. These results are comparable to the best outcomes reported in the literature, with the advantage of eliminating the need for interlayers or additional external surface pretreatment equipment.