Thermal aging of painted galvanized steel after mechanical deformation

In the present work the effects of thermo-mechanical degradation on the protective properties of coil coated samples are studied. A cupping test was performed, with penetration depths of 2, 4 and 6 mm and a finite-element model was set to define the local strain for the different depths of penetration. Different thermal stresses were applied to accelerate the natural weathering: a thermal cycle with a maximum temperature of 45 °C was chosen to simulate the stress occurring in the outdoor exposure, a second thermal cycle (maximum temperature 95 °C) was proposed as 1-week accelerated testing procedure. The effects of the thermo-mechanical stress were studied by electrochemical impedance spectroscopy. The ageing procedure and the electrochemical measurements were useful to evaluate the barrier and adhesion properties for the various coating formulations and to define the influence of the different strain levels.