AA 1050 Aluminum lithographic plates were electrograined in nitric and hydrochloric acids using various ac current waveforms. Detailed etch pit morphology and etch film microstructure were characterized by cross-sectional transmission electron microscopy (TEM). After electrograining, an etch film deposited on the Al surface and masked its real topography, which exhibited a pitted surface after removing the etch film. The etch film morphology strongly depended on the electrolyte composition, and the frequency and waveform of the ac current. For example, the etch film formed in nitric acid exhibited a layered structure, whereas that formed in hydrochloric acid was a single layer. Moreover, the layer thickness of the etch film decreased with increasing frequency and anodic/cathodic charge ratio of the ac current, indicating that the etch film formed during the cathodic half cycle. The layered etch film thus developed when the etch film overlaying the Al surface underwent dissolution /peeling during successive cycles.
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