Trends in corrosion–resistant precoated steel sheets for automotive applications

Trends in corrosion resistant precoated steel sheets for automotive application in Japan were investigated. There are two concepts of the use of precoated steel sheets for perforation corrosion prevention: the use of metal–coated steel sheets and the use of weldable prepainted steel sheets. As for the metal–coated steel sheets, one–side–coated galvanized, galvannealed and electrogalvanized steel sheets have long been used. Recently some kinds of electroplated alloy coated steel sheet have been developed. Among them, Zn–Ni–Co, double layer Zn–Fe and Zn–Fe/Zn–Ni double layer coated steel sheets have been put to practical use. As for the weldable prepainted steel sheets, Zincrometal has long been used. To solve the problems of Zincrometal in formability and galvanic protection effect, metal–organic composite coated steel sheet having a weldable paint film upon zinc alloy coating layer has been developed and put to practical use. Comparison of performances of these precoated steel sheet were discussed.