Corrosion Protection Fundamentals of Metal-Finished Steel Sheets for Automotive Applications 830871
Corrosion protection mechanism was investigated on newly developed-metal-finished steel sheets for automobile applications. Such alloying elements to zinc as Ni, Co, Mn, Mg and Al retard oxygen reduction reaction because of their stabilizing effect of Zn(OH)2 films, leading to improved corrosion resistance. Wet adhesion of cathodic primed full painted system is governed by alkali-induced dissolution of phosphate and zinc coatings during electrocoating. Fe in coating layer improves wet adhesion because of its high alkali-resistance. Both Fe and Ni have a pore blocking effect on phosphate films, with resultant a superior paint performance. The factors affecting perforation of jointed panels were also discussed.