Electrolytically colouring anodised aluminium - is carried out after two step anodising using first sulphuric acid then phosphoric acid electrolyte

摘要

In a first step, Al is anodically treated in an electrolyte contg. mainly H2SO4. In a second step, anodic treatment is continued in an electrolyte contg. mainly H3PO4, pref. at direct voltage 20-30 v, before the final electrolytic colour treatment. Colour treatment takes place by standard process, by applying a current between anodically treated Al and a counter-electrode, while Al is immersed in a bath contg. a selected metal salt. Used for Al panels or window frames exposed to weathering. 2-step process leads to a wide range of colours in colour-treatment step. A wider range of colouring electrolytes can be used.