2021 Volume 61 Issue 10 Pages 2620-2628
Outdoor exposure tests of prepainted 55% Al–Zn steel sheets are performed for 24 months at five different exposure sites: Tokyo, Kagoshima, and Okinawa in Japan, and Arizona and Florida in the United States. The anticorrosive pigments in the primer with topcoat are strontium chromate (Cr), magnesium vanadate + zinc phosphate (MgV/ZnP), calcium silicate (Si), and magnesium vanadate (MgV). The edge creep is evaluated by measuring the creep width every six months. The electrochemical impedance and polarization curves of the non-coated 55% Al–Zn steel and carbon steel (CS) are measured in a 3% NaCl solution suspended with the anticorrosive pigments. The corrosion products at the cut edge are analyzed by scanning electron microscopy and energy dispersive X-ray spectrometry.
The edge creep for all the specimens did not progress at all in Arizona (dry desert), although red rust appears on the CS surface at the cut edge. At Kagoshima and Okinawa (marine atmospheres), the progress of the edge creep is fast for all the specimens. It is especially significant in Okinawa where temperature and humidity are high. When comparing the effects of the pigments on the edge creep properties, the results show that Si is poor at all exposure sites except Arizona, and MgV/ZnP shows edge creep properties comparable to Cr. From the anodic polarization characteristics of 55% Al–Zn steel and the cathodic polarization curve of CS, the effect of the pigments on edge creep is successfully described.
