Coloured anodic coating on aluminium - produced by voltage impulses in sulphuric acid electrolytes in range 25-45 volts

摘要

Coloured coatings are produced on Al or Al alloys by anodic oxidn. in an H2SO4 electrolyte in which voltage pulses of 25-45 V are applied for durations of 5-70msec. The proportion of impulse frequency to duration ('n') is pref. 2-7 and the current density is 2-8A/dm2 and the specific resistance of the bath is controlled by addns. The process allows the prodn. of coatings of good colour that are obtd. by high voltages to be obtd. with H2SO4 electrolytes.