Time-variable current regimes for the surface modification of high-strength aluminium alloys by anodic oxidationWednesday (28.09.2016) 11:15 - 11:30 Part of:
High-strength aluminium alloys offer a great potential for saving weight by replacing steel as a construction material. The corrosion and wear resistance of these alloys can generally be improved by anodic oxidation. During the anodic oxidation, the aluminium substrate is electrochemically converted to alumina in an electrolytic process. The result is a surface of oxide-ceramic nature, which offers superior hardness and enhanced chemical resistance compared to the metallic substrate and can further be functionalised, e.g. by incorporating colorants, lubricants or corrosion inhibitors into the characteristic pore structure of the coating. However, strength-giving alloying elements in the aluminium substrate tend to disturb the anodic oxidation process with deteriorating effect on both the structure of the coating and its properties. In contrast, recent research indicates a beneficial effect of time-variable electrical regimes for the anodic oxidation process. In the present work, the effect of pulsed current, stepwise-increased current and current ramps during the anodic oxidation of AlCu4Mg1 (EN AW-2024) was examined in comparison to the electrolyte temperature and electrolyte composition by means of a design of experiments (DOE). The thickness of the produced oxide coatings, their morphology, hardness, pitting corrosion potential and resistance against indentation of foreign objects under relative motion (scratch test) as well as the amount of electrical energy used for the oxide coating formation were evaluated in dependence of the process parameters. The significance of the effects of the considered parameters on the mentioned properties was assessed by an analysis of variance (ANOVA). Both the statistical and the technological relevance of different approaches concerning time-variable electrical regimes during the anodic oxidation were testified.