Cut-Edge Corrosion Behavior of Prepainted 55% Al–Zn Steel with Chromate-free Primers in Various Atmospheric Environments

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.