Application of experimental design for AA6351 aluminum alloy anodization and coloring

In this work, we used statistical methodologies to study the influence of anodizing and coloring parameters on surface protection of AA6351 aluminum alloy in Na₂SO₄ 0.5 mol L⁻¹ at pH 4 employing electrochemical measures as response. The parameters used (independent variables) were the anodization current density (A), anodization time (B), dye concentration (C), and electrolyte concentration (D). The response surface methodology (RSM) was used for the optimization of the aluminum anodization process and coloring. The charge transfer resistance (CTR) was used as the response. For this analysis, a factorial 2⁴ experimental design was developed, and all parameters were varied at two different levels in addition to the central point. The adjustment of the statistical model and the influence of the parameters used was investigated using the analysis of variance (ANOVA), and the quadratic model had the best fit. This analysis showed that A is the most significant parameter among those used. Furthermore, the RSM used indicated that the optimal conditions for the protection of anodized and colored aluminum occurred when a higher anodizing current density was applied for short periods and low dye concentrations. The RSM results also showed that the inverse is valid and that parameter C does not influence the results. To validate the results of this study, the open circuit potential and potentiostatic anodic polarization were measured, and electrochemical impedance spectroscopy was also used. In addition, optical micrography and scanning electron microscopy were used to investigate the effects of the different parameters on the surface modification. Therefore, the statistical model reveals how to obtain an anodized and colored aluminum less expensively than current methods by selecting the optimal amount of energy and chemicals for the treatment process. (paper)