Study of Electrochemical Behavior of Commercial AA5052 during Anodizing in Phosphoric Acid Solution in Relation to Mg Species Content in Films

Abstract

The effect of anodizing temperature (10–50°C) at each particular stage of the anodizing process of the commercial AA5052 in 0.4 M H3PO4 at 30 V is studied in relation to the concentration of Mg species in the oxide layer. An advantageous behavior of the alloy is observed in comparison with pure aluminum, especially at 30°C. However, an impediment of anodizing is observed, leading to a reduction of the benefits of AA5052, which is correlated with a reduction in the Mg/(Mg + Al) atomic ratio for the oxide layer compared to the bulk alloy estimated by SEM/EDS analysis. These phenomena become more intense as the anodizing time and temperature rise. For example, a thrice higher oxide layer thickness at stage III in comparison with pure aluminum becomes twice higher at stage IV at 30°C. The duration of stage III is affected, but not that of stages I and II, which are completed in a short time and in which only a slight retardation of the increase in the density of the consumed electric charge was observed. The porosity increases with time but at the end of stage III reduces slightly, at T above 30°C, in spite of the general aspect that it remains stable or increases slightly with temperature.