Tailored AA1050 alloy surfaces by electrograining

The effects of anodic and cathodic polarisation during ac electrograining of aluminium AA1050 alloy in nitric acid on the resultant surface appearance have been examined. A strong dependency of the surface convolution on the amplitude of the anodic and cathodic polarisation is revealed. Cathodic polarisation promotes pit initiation and suppresses pit growth; consequently, a high population of fine hemispherical pits is observed after electrograining with cathodic bias. The passive region of anodic polarisation below the pitting potential is associated with dissolution of segregates and second phase material from the filmed macroscopic alloy surface, which influences the pit initiation stage. Anodic polarisation above the pitting potential encourages pit growth. Thus, by controlling the extents of anodic or cathodic polarisation and by consideration of the local interfacial solution conditions, the means for developing tailored and optimised pit morphologies is revealed.