Optimization of process parameters for 4643 Al alloy anodization in mixed oxalic/phosphoric electrolytes: Doehlert experimental design

Abstract

The anodization technology is commonly used for surface enhancement for aluminum and its alloys. It is widely used to improve the hardness and corrosion resistance of aluminum alloys. In the present work, the Doehlert experimental design was used to optimize the film generated on aluminum during anodization in oxalic or phosphoric solutions. The research assessed the oxide layer thickness (T_OL) and practical oxide layer efficiency (${\eta }_{\mathrm{POLE}}$) based on variables such as temperature, electrolyte concentration, current density, and exposure duration. According to the Doehlert experimental design, 25 tests are achieved for each response function. The anodized aluminum samples are tested in an aggressive saline solution via electrochemical techniques. The open-circuit potential measurements showed that steady-state potentials are approached after 40 minutes. The polarization measurements showed that corrosion current density decreased with an increase in layer thickness. Maximum protection efficiency was 97 % at optimum layer thickness. Electrochemical impedance spectroscopy measurements indicated that the metal's resistance increased with the thickness of the layer, corroborating the polarization findings. The outcomes of the experimental design and mathematical modeling show that all process-independent variables are significant. Furthermore, the interaction between the independent variables on the thickness of the oxide layer and the practical oxide layer efficiency is very considerable. The optimum T_OL and ${\eta }_{\mathrm{POLE}}$are 25.5459 μm and 0.976, respectively. These results were further validated through surface morphology analyses.