Abstract: A twice-anodized aluminum substrate is anodized sequentially in first and second aqueous electrolytes. In the first, the substrate is conventionally anodized to produce (i) a porous anodic oxide layer having open pores and a passivation layer thereunder. The substrate, now singly-coated, is then anodized in the second electrolyte of an aqueous solution of an organophosphorus compound which generates a residue which is chemisorbed and covalently bonded to the substrate to form (ii) a monomolecular essentially continuous monolayer on the outer surface of (i), and at the same time, the second anodizing step produces (iii) a barrier layer of non-porous aluminum oxide under (i). The thickness of this barrier layer can be increased as a function of the voltage used while maintaining the thickness of (i) substantially constant, and (ii) protects (i) from dissolution.

Abstract: A process for zinc electroplating of aluminum strip which can be performed continuously at a high speed and a high current density. The process comprises subjecting aluminum strip to anodic electrolysis in an acidic solution which may be an acidic plating bath solution or a pickling solution before the strip is subjected to cathodic electrolysis in an acidic zinc plating bath to perform zinc electroplating.

Abstract: The present invention provides a process for surface treatment in which the surface of aluminium or its alloy can be put in a desired color and the improved wear resistance and corrosion resistance can be obtained. Anodic oxidation coatings obtained by conventional alumite treatment is porous and thus is small in wear resistance and in corrosion resistance and is insufficient in durability of coloring. The process of the present invention is characterized in that the process comprises the steps of: forming anodic oxidation coatings by conventional method on the surface of the aluminium or its alloy, thereafter applying an alternating voltage of 10 V.about.30 V within a sulfate solution or nitrate solution of a desired metal to a member on which said anodic oxidation coatings was formed by the above step, whereby said metal is electrolytically impregnated into said anodic oxidation coatings.