Process for electrolytically coloring aluminum or aluminum alloy workpieces comprises anodizing the workpiece to form a covering layer, treating layer with a direct current and coloring the workpiece in an electrolytic solution

摘要

Electrolytic coloring of aluminum or aluminum alloy workpieces comprises anodizing the workpiece in an aqueous strongly acidic electrolytic solution using a direct current or alternating current with a current density of 0.5-3.0 A/dm2 forming an oxidic porous covering layer; treating the covering layer with a direct current in a bath having a high conductivity of 200-600 mS/cm; treating with an alternating current in a modifying bath and coloring the workpiece in an electrolytic solution containing a metal salt as coloring agent. Process for electrolytically coloring aluminum or aluminum alloy workpieces comprises anodizing the workpiece in an aqueous strongly acidic electrolytic solution using a direct current or alternating current with a current density of 0.5-3.0 A/dm2 forming an oxidic porous covering layer; treating the covering layer with a direct current in a bath having a high conductivity of 200-600 mS/cm; treating with an alternating current in a modifying bath and coloring the workpiece in an electrolytic solution containing a metal salt as coloring agent. The value of the direct current density is adjusted to at least three times the current density used during anodization but bot less than 2.0 A/dm2. The electrolytic solution used in the modifying bath contains a strong acid and an organic compound selected from polyalcohols, hydroxy acids or dihydroxy acids.