Improvement of corrosion protection system for aluminium body bus used in public transportation

In this work, the corrosion protection of aluminium body bus is investigated starting from the failure analysis of paint protection system of bus that served Italian urban area for a few years. Considering the service failures found on the panels of several busses, it is possible to observe that the delamination damages and paint blisters are localized in correspondence with the aluminium sheets joints. Therefore, the joints are the critical points, which promote the start of the degradation process. Probably, the insufficient performances of the organic coating leads to an increase of the degradation phenomenon in time, with the formation of blisters and detachment of paint parts. The improvement of the protection system is obtained using a primer, deposited through a cataphoresis process, and a modified joint geometry. The cataphoretic primer shows superior corrosion protection properties in respect to the standard-deposited layer, and improves the adhesion properties and delamination resistance of the organic coatings system. The new join geometry eliminates the presence of interspaces between the panels avoiding possible infiltrations of aggressive solution, and improves the blistering and delamination resistance of the paint.