Etch Film and Pit Structure of AA1050 Aluminum Plates Electrograined in Nitric and Hydrochloric Acids

Abstract

AA1050 aluminum lithographic plates were ac electrograined in nitric and hydrochloric acids. The surface morphology of the electrograined aluminum plate was characterized via scanning electron microscopy. In addition, detailed internal structure of the etch pits was examined using an epoxy replica method. The microstructure of the etch film was characterized by cross-sectional transmission electron microscopy. Experimental results indicate that the etch film overlaying the individual pit formed in nitric acid was a layered amorphous structure. Each layer of the etch film assumed the shape of the individual pit on which the etch film overlaid. Conversely, an amorphous etch film, which was not a layered structure, covered the fine pit formed in hydrochloric acid. The different filming behaviors observed were owing to the anions associated with the electrolytes, i.e., and of which the former aggressively induces the pitting corrosion on most aluminum alloys. Moreover, the morphology and size of the etch pits differed for the electrolytes employed. That is, the hemispherical individual pits led to the formation of convoluted pits formed in nitric acid, whereas the coalescence of fine pits caused the formation of convoluted pits during electrograining in hydrochloric acid. Our results further demonstrated that the individual pits formed in nitric acid were significantly larger than the fine pits formed in hydrochloric acid. © 2001 The Electrochemical Society. All rights reserved.