Characterization of friction stir-based linear continuous joining of aluminium alloy to structural polymer

Dissimilar continuous joining of lightweight metal alloys to structural polymer is a major manufacturing challenge, demanding feasible and reliable solutions. Through-slot extrusion joining (TSEJ) is a friction stir-based processing technique investigated in the manufacturing of continuous linear joints between aluminium alloy AA5754 overlapping structural polymer polyether ether ketone (PEEK). An intermediate rigid and thin titanium extrusion die protects the polymer locally from thermal degradation and promotes the formation of a continuous double hook-like feature of extruded aluminium into the polymer component along the joint path. The structure of the joint provides macro-mechanical interlocking between the joined components. A set of four tools, and other key process parameters, were investigated for process stability, tensile-shear strength, and microstructure. The best TSEJ condition is chosen for microstructural analysis via optical microscopy and scanning electron microscopy. Three distinct failure modes were identified. The best condition provided an average tensile-shear load of 110 kN/m. The tool position with bias toward the flow side of the extrusion slot shows to improve the strength of joints. The microstructural analysis along the interface of AA5754 to PEEK exhibits micro-mechanical interlocking, intercalated layers of these materials and adhesion as joining mechanisms.