Anodic oxidation of the AlCu4Mg1 aluminium alloy with dynamic current control

The anodic oxidation process is a common method for the surface modification of aluminium and its alloys. The increasing application of high-strength aluminium alloys therefore represents a challenge, since alloying elements, amongst them copper, significantly disturb the coating formation during anodising. Hence, flaws arise in the oxide layers and lead to the deterioration of their performance. Recent investigations have indicated the possibility of extenuating the negative influence of the alloying elements on the coating formation by applying time-variable electrical regimes. In case of the current density as the control factor in the coating process, this approach is related to as dynamic current control. For the anodic oxidation of AlCu4Mg1 (EN AW-2024), the effect of dynamic current control on the oxide layer properties is investigated by using a design of experiments (DOE). The parameter variation includes starting ramps, a step-wise change of the current density in the process and pulse current at electrolyte temperatures of 5 °C and 15 °C. A solution of 20 vol% sulphuric acid with an addition of oxalic acid or nitric acid is used as the electrolyte. The produced oxide coatings are examined with regard to their thickness, hardness, their performance in the scratch test and their current density-potential behaviour in diluted NaCl solution. Further, the electrical energy consumption during the anodisation is considered. The results are evaluated with the help of an analysis of variance (ANOVA).