Microstructural and interface properties of aluminium alloy coatings on alumina applied by friction surfacing

Two large groups of materials, namely metals and ceramics, are used in mass quantities in today’s industry because of their outstanding properties. To achieve higher product performance dissimilar materials need to be combined in assemblies, but their joining is challenging. Using friction surfacing technology Al₂O₃ ceramic substrates were coated with an aluminium alloy (AlMg4.5Mn0.7). Earlier research by the authors suggested that two major bonding mechanisms, namely mechanical interlocking and van der Waals forces, are responsible for the bonding strengths achieved between the coating and the substrate. Further scanning electron microscopy, scanning transmission electron microscopy, high-resolution transmission electron microscopy and energy dispersive X-ray spectroscopy analysis at a sub nanometre resolution were conducted and are presented in this article. These analytical methods revealed that the aluminium coating and the Al₂O₃ (Formula presented.) grains form a sharp boundary without evidence of either a chemical reaction or diffusion at the interface and suggest that the main bonding mechanisms for the Al/Al₂O₃ (Formula presented.) system are van der Waals forces. In addition, mechanical interlocking may serve to hold in position the interface surfaces, to preserve their close proximity, allowing the van der Waals forces to persist.