Investigation on adhesive joining of additively manufactured ULTEM 9085 and ALSi10Mg: effect of adhesive type and substrate characteristics

In this work, the adhesive bonding behaviour of joints between FDM-manufactured ULTEM™ 9085 and LPBF-produced AlSi10Mg was experimentally investigated under as-built surface conditions, deliberately avoiding any surface pre-treatment to assess the intrinsic bonding capability of different adhesive systems. Three commercially available structural adhesives with distinct chemistries were considered: an epoxy (Araldite ® 420 A/B), a methacrylate (Plexus MA832) and a cyanoacrylate (LOCTITE ® 401). Single-lap shear tests were carried out according to ASTM D3163-01, while the fracture mechanisms were investigated through optical microscopy, SEM observations and EDS microanalysis. The mechanical response was interpreted considering the combined contribution of adhesive chemistry, the controlled characteristics of the FDM-manufactured ULTEM™ substrate and the different as-built surface conditions of the LPBF AlSi10Mg adherends. Araldite ® 420 A/B exhibited the highest lap-shear strength together with predominantly cohesive fracture behaviour and limited sensitivity to the investigated surface conditions. Plexus MA832 showed the lowest mechanical performance, with failure mainly occurring at the polymer/adhesive interface, whereas LOCTITE ® 401 exhibited intermediate strength associated with a mixed cohesive/adhesive fracture mechanism. Overall, the study demonstrates that, in hybrid AM polymer–metal joints, the dominant factor controlling adhesion shifts from adhesive bulk properties to interfacial compatibility or substrate morphology depending on the adhesive system. These findings provide useful insights for the design of reliable and sustainable joining strategies using as-built surfaces.