Interpretation of the anodic and cathodic potential variations during the AC-graining of aluminium in hydrochloric acid

The variations of the anodic and cathodic amplitudes during the AC-graining of aluminium in hydrochloric acid electrolyte were investigated in this work in order to combine the amplitude variations with the electrochemical reactions that take place in the electrograining process. Aluminium samples were galvanostatically grained in 0.34M hydrochloric acid and the signal of the applied potential versus a reference electrode was recorded by a high frequency acquisition system. The potential variation during the AC-graining of the aluminium alloy AA1050 and of pure aluminium (99.99%) was examined as well as the influence on the potential variation of the applied pre-treatments. In addition, scanning electron microscopy and backscattering electron micrographs were also used to examine the aluminium samples. The smut layer formation at the initial stages of graining was investigated by X-ray photoelectron spectroscopy. It was concluded that the variations of the anodic and cathodic amplitudes were divided into three different regions. An interpretation of these regions was achieved by the combination of the potential measurements of the different example substrates with the subsequent observations of the grained surfaces. By using this interpretation of the potential variations, interesting information can be obtained about the influence on the electrograining process of the aluminium substrate, the applied pre-treatments and the electrograining conditions.