To provide a coated steel sheet which is provided with both of sufficient working performance and corrosion resisting performance even to application where a high working degree is applied, to provide a Zn-Al alloy plated steel sheet as the base material thereof, and to provide their production methods.
The method comprises: a first stage where an Al-Zn based alloy plating film comprising, by mass, 40 to 70% Al and Si by 0.5 to 5.0% of the Al content is formed on the surface of a steel sheet; a second stage where 0.3 to 2% elongation is imparted to the steel sheet after the formation of the plating film; a third stage where, after the second stage, the steel sheet is subjected to heat treatment so as to be held at 180 to 250°C for 10 to 30 hr; a fourth stage where a coating substrate layer is formed at least on one side of the heat-treated steel sheet; and a fifth stage where at least one layer of a coating film is formed on the upper layer of the substrate layer.
TOKI TAMOTSU
TAKAHASHI MICHIYASU
IKISHIMA KENJI
SUMITOMO METAL STEEL PROD
Akihiko Yamashita
Kishimoto Tatsuto