THE INFLUENCE OF MANGANESE ON THE AC ELECTROLYTIC GRAINING OF ALUMINUM

The AC electrograining of aluminium involves the application of an alt ernating voltage or current between aluminium electrodes in a suitable electrolyte, to produce uniformly roughened surfaces for lithography. The resultant morphology is dependent upon the electrical, solution a nd substrate conditions employed. Here the influence of substrate cond itions is investigated. The investigation was focused on the influence of manganese, manganese being the element which distinguishes the com mercially two most commonly employed aluminium alloys for the manufact ure of lithographic plates. The influence of manganese present in soli d solution or in intermetallic particles was investigated for AC elect rolytic graining in both hydrochloric and nitric acid. The degree of u niformity of the final morphology obtained by treatment in both hydroc hloric and nitric acid increases with decreasing amount of manganese p resent in solid solution. For AC electrograining in hydrochloric acid the influence of manganese on the graining behaviour only becomes evid ent in the second stage of treatment, where hemispherical pits are cre ated. During the etch attack, compositional or metallurgical features have only a minor influence. The influence of manganese on AC electrog raining of aluminium in nitric acid is evident from the very first sta ge of treatment.