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2010-11-18 - Colloque/Présentation - communication orale - Anglais - 1 page(s)

Recloux Isaline, Poelman Mireille , Cornil Nathaël, Blandin Nathalie, Deronne Laurent, Le Disert Yves, Olivier Marie-Georges , "Electrochemical study of the corrosion behaviour at the edges of electrocoated steel" in 8th International Symposium on Electrochemical Impedance Spectroscopy, Carvoeiro, Portugal, 2010

  • Codes CREF : Corrosion des matériaux (DI2114)
  • Unités de recherche UMONS : Génie des Procédés chimiques et biochimiques (F505), Science des Matériaux (F502)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux), Institut des Sciences et du Management des Risques (Risques)

Abstract(s) :

(Anglais) Cathodic electrocoating is widely used as a primary protective layer in the automotive industry. The electrocoat products have excellent throw-power, i.e. can cover even difficult to reach areas of complex parts. Despite this unique ability, electrocoats cannot offer a completely uniform coverage. Indeed, at the beginning of the electrocoat baking, the painting tends to flow away from sharp edges resulting in low film build. The corrosion process may then firstly begin along these relatively unprotected areas through a delamination or a blistering phenomena. In order to avoid this particular and harmful corrosion, high-edge coverage electrocoats, containing rheological modifiers that control the flow during the baking, were developed. Different standard weathering tests are today defined to evaluate the edge corrosion. One of these is a 7 days salt fog exposure of coated steel knife blades. After exposure, the corrosion is evaluated by counting the rust spots along the edge of blade. However, as the method is rather qualitative and is strongly dependent on the operator who performs the evaluation, there is a necessity to develop new testing methods. Electrochemical techniques and in particular electrochemical impedance spectroscopy are good candidates to provide a more precise, quantitative and reliable evaluation of anticorrosion protection at edges. This work aimed at implementing all these tests on electrocoated steel knife blades in order to evaluate their edge corrosion sensitivity. Two e-coat differing by their content in flow modifier were compared. The pretreatment of automotive parts, under electrocoat, is also an important factor for the development of corrosion at edges. As part of this study, two different pretreatments were also applied on the steel knife blades and compared: a classical trication phosphatation and a new pretreatment named ZircobondTM developed by PPG Industries. The electrochemical methods used are potentiodynamic cathodic polarization, electrochemical impedance spectroscopy and ac/dc cycles. All the measurements were performed in 0.5 M aerated sodium chloride solution. An excellent correlation was observed between the electrochemical measurements and the salt spray results. Electrochemicals measurements, less consuming time, are even more sensitive. Indeed, while salt spray test didn’t allow to differentiate some electrocoats, electrochemical measurements, on the other hand, allowed to demonstrate the better performances of an e-coat containing a higher amount in flow modifier.