PURPOSE: To improve formability, weldability and corrosion resistance by forming an Al oxide film containing a specified amt. of Mg oxide on the surface of an Al material and further forming a lubricating inorg. compd. layer comprising hydrated borate of alkali metal thereon.
CONSTITUTION: An Al oxide film having ≤20% Mg oxide content is formed to 10-200 film thickness on the surface of an Al material. Then, a lubricating inorg. compd. layer comprising hydrated borate of alkali metal is deposited in an amt. of 10-1000mg/m2 thereon. It is preferable that the dissolution residue of the lubricating inorg. compd. layer with water washing or alkali degreasing is <1mg/m2. By controlling the proportion of Mg oxide in the surface oxide and film thickness, good weldability and enough corrosion resistance is obtd.
ISHIDA YOJI
NANBAE MOTOHIRO
TANI TOSHIO
KATO OSAMU
UESUGI KOJI
KAWASAKI STEEL CO