Method for electrolytic coloring of aluminum surfaces using alternating current

摘要

PCT No. PCT/EP93/03574 Sec. 371 Date Jul. 28, 1995 Sec. 102(e) Date Jul. 28, 1995 PCT Filed Dec. 16, 1993 PCT Pub. No. WO94/15002 PCT Pub. Date Jul. 7, 1994Anodized aluminum surfaces are electrolytically colored using alternating current in a process in which two different coloring baths are sequentially employed. One bath contains copper(II) ions and an additive which improves throwing power thereby providing uniform distribution of the depth of color. The other bath contains tin(II) ions, silver ions, or both tin(II) and silver ions. If tin(II) ions are included, additives which stabilize tin(II) ions and improve throwing power are also included. Either bath may be used first. The use of two separate coloring baths provides colored aluminum surfaces which have excellent resistance to corrosion. Workpieces with reddish-gold hues and darker tones can be produced.