The influence of manganese on the AC electrolytic graining of aluminium

The AC electrograining of aluminium involves the application of an alternating 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 and substrate conditions employed. Here the influence of substrate conditions is investigated. The investigation was focused on the influence of manganese, manganese being the element which distinguishes the commercially two most commonly employed aluminium alloys for the manufacture of lithographic plates. The influence of manganese present in solid solution or in intermetallic particles was investigated for AC electrolytic graining in both hydrochloric and nitric acid. The degree of uniformity of the final morphology obtained by treatment in both hydrochloric and nitric acid increases with decreasing amount of manganese present in solid solution. For AC electrograining in hydrochloric acid the influence of manganese on the graining behaviour only becomes evident in the second stage of treatment, where hemispherical pits are created. During the etch attack, compositional or metallurgical features have only a minor influence. The influence of manganese on AC electrograining of aluminium in nitric acid is evident from the very first stage of treatment.