EFFECT OF BENZOTRIAZOLE ON THE EFFICIENCY OF ANODIZING OF AL-CU ALLOYS

The influence of benzotriazole, at concentrations to 10 g l(-1), on th e efficiency of anodizing of Al-3.5 wt% Cu alloy at constant current d ensity in 0.1 M ammonium pentaborate electrolyte has been investigated for two conditions of the alloy, namely solution-treated and solution treated and artificially aged. For the solution-treated alloy, the ad dition of benzotriazole has negligible effect on the voltage-time resp onse and, hence, also the efficiency of film growth, which was about 9 2% for film formed to 200 V. In contrast, benzotriazole increases sign ificantly the efficiency of film growth on the solution-treated and ag ed alloy, from similar to 45 to similar to 70% for films formed to 200 V. The increased efficiency is attributed mainly to the inhibition of oxygen evolution on CuAl2 particles by formation of a polymeric, Cu-I -benzotriazole film on the copper-rich phase. The influence of benzotr iazole, from comparisons of voltage-time responses for both heat treat ments of the alloy, is greatest at the commencement of film growth and subsequently diminishes, with little, or no, effect following film fo rmation to 150 V. The diminishing influence is associated with eventua l growth of relatively thick anodic film, which limits oxygen evolutio n. (C) 1997 Elsevier Science Ltd.