Plasma Electrolytic Oxidation (PEO) has received much attention in research for the production of oxide coatings with excellent tribological performance and corrosion resistance. This study looks into a further application of PEO as an alternative to conventional anodizing techniques for the preparation of aluminium parts for bonded structures in the automotive industry. Adhesive bonded aluminium parts have become increasingly important to the industry where lightweight structures are imperative to performance. Conventional anodizing processes have been applied to adhesive bonded aluminium components to promote increased bond durability and corrosion resistance tracing back to the first half of the 20th century. However, Conventional anodizing procedures generally use strongly acidic electrolytes which have a substantial environmental impact. Anodizing procedures are generally multi-stage processes which can be resource intensive and time consuming. PEO offers an alternative route for the production of well adhered oxide coatings where weak alkaline electrolytes can be utilised in place of the highly acidic electrolytes associated with conventional anodizing processes. PEO has the further potential to reduce the number of additional treatments prior to and after the anodizing stage offering scope for resource and time saving.
Work has been carried out to produce thin PEO coatings on aluminium alloys with a view to providing good adhesive bonding and corrosion resistance. Through the use of varying processing parameters and different electrolyte compositions, coatings with properties designed to promote enhanced bond strength are being developed. Topological features of the developed PEO coatings, including surface porosity which is important for the promotion of mechanical interlocking in the adhesive bond have been analysed. Work has been undertaken to analyze the chemical composition of the coatings formed and how this effects the properties in terms of adhesive bond strength and corrosion resistance. As a result, a scientific description as to how the surface features of PEO coatings contribute to adhesive bond durability is being summated, which will lead to further optimisation of PEO coatings for this application in the future.