Assessment of Resistance to Delamination of Coil Coated Steel

Abstract

The evaluation of the protective properties of a coating relies mostly on field tests and on accelerated tests such as salt spray. The resulting damage can be evaluated through visual inspection or through mechanical tests such as pulloff, to describe the development of the corrosive phenomenon and the loss of adhesion of the coatings. Following the recent experience of the Bierwagen group, the present paper proposes an aging test in which temperature was used to accelerate natural weathering, and the damage of the coating was evaluated by electrochemical impedance spectroscopy. The tested samples were coil coated panels exposed to a 0.3%Na₂ SO₄ test solution. A two time constants equivalent electrical circuit was used to simulate the electrochemical behaviour of the coated systems. The evolution of circuit parameters was evaluated. In particular, it was possible to determine the adhesive properties of the samples through the evolution of the second time constant. These trends were then compared with the changes in the first time constant and with the state of the coating surface after the aging test. The advantages and the limits of the procedure are evaluated and discussed.