Joining of additively manufactured fiber-reinforced thermoplastic and metals by ultrasonic energy: Mechanical and corrosion behavior

Ultrasonic joining (U-Joining) is applied to create reinforced hybrid joints between unreinforced or fiber-reinforced polymers and surface-structured metals. While the feasibility of joining additively manufactured (AM) materials was already demonstrated, a detailed description of the process parameters’ effects is still missing. Therefore, this study aims to define the influence of the U-Joining parameters on the mechanical and corrosion properties of AM 20% short-carbon-fiber-reinforced poly-ether-ether-ketone (PEEK-20CF) and 316L stainless steel (316L SS) hybrid joints. Optimal joining parameters were determined via Box-Behnken design of experiments to maximize the joints’ ultimate lap shear forces (ULSF) and displacement at break (DaB), where the results increased from 1.4 ± 0.2 kN to 3.6 ± 0.3 kN (2.6 times) and from 1.2 ± 0.3 mm to 2.4 ± 0.1 mm (2 times), respectively. Microstructural analyses revealed a strong micromechanical interlocking between the parts due to the filling of crevices at the as-built AM metallic part’s rough surface by consolidated PEEK-20CF, which resulted in a mixture of adhesive, cohesive and net tension failure during the lap-shear tests. Finally, the corrosion resistance was also evaluated by potentiodynamic polarization curves, showing that the energy input during the joining cycle slightly reduced the pitting corrosion resistance of the 316L part.