Experimental Investigation, Modeling and Optimization of Parameters in Hard Anodizing of 6063 Aluminum Alloy Using Central Composite Design

Aluminum alloy forms a protective layer of aluminum oxide when exposed to air, which gives it corrosion resistance. But, the layer can be easily damaged, causing metal corrosion. The hard anodizing method is used to solve this issue. Determining the appropriate anodizing parameters, including current density, process time, and electrolyte concentration, is crucial for attaining the desired thickness and hardness of the anodized layer. An experimental design approach utilizing the response surface method (RSM) was employed to investigate the effects of these variables. Quadratic models were presented to predict the hardness and thickness of the layer with an average error of 2.84% and 3.89%, respectively. The models were verified through analysis of variance (ANOVA) to assess the effect of each parameter and their interactions. Oxalic acid concentration, the interaction between process time and oxalic acid concentration, and the square of current density and process time have a significant impact on hardness. Layer thickness is mainly influenced by current density, process time, and the interaction between process time and oxalic acid concentration. Optimization results show that a current density of 1.19A/dm(2), a process time of 160 min, sulfuric and oxalic acid concentrations of 26.25 gr/li t and 36.88 gr/li t, respectively, leads to hardness of 434 HV and thickness of 93.6 mu m. A scanning electron microscope (SEM) image under optimal conditions shows that aluminum porous arrays created by an anodizing process in mixed sulfuric acid and oxalic acid electrolyte, with a hexagonal shape observed across a wide range of grain domains.