Effect of the surface morphology of SLM printed aluminium on the interfacial fracture toughness of metal-composite hybrid joints

Selective laser melting (SLM) is a state-of-the-art additive manufacturing (AM) process for producing complex metal components. For metal components produced by the SLM process, a poor surface quality can be a concern, as the rough surface could initiate surface cracks early under static or fatigue loading and negatively affect the dimensional tolerance. However, the inherently rough surface has potential to eliminate the necessity for additional surface treatment for adhesive bonding. In this work, the influence of the printing angle (45º – 90º) on the surface morphology of SLM manufactured parts and thus its impact on the interfacial fracture toughness of aluminium/carbon composite joints bonded with epoxy adhesive was investigated experimentally. The surface roughness analysis showed that as the printing angle increased, the roughness of the upper surface of the SLM printed part increased in general, while the lower surface showed the opposite trend. The single-leg bending tests results showed that the inherent surface roughness of the printed part significantly improves the interfacial fracture toughness (from 289 J/m2 to 747 J/m2) and is much more effective in the prevention of interfacial crack propagation in comparison to the surface mechanically abraded after printing.