Optimization of anti-corrosion ability of micro-arc oxide coating on AZ91D alloy using experimental strategies

The effects of anodizing variables in a micro-arc process (MAO) for improving anti-corrosion ability of an oxide coating on AZ91D alloy were systematically examined using fractional factorial design (FFD), path of steepest ascent study, and the central composite design (CCD) coupled with the response surface methodology (RSM). The FFD study indicates that the main and interactive effects of treatment time and hexamethylenetetramine (HMTA) concentration are the key preparation factors influencing the oxide coating. Empirical models for roughness value (Ra) and corrosion resistance (Rs) are fitted against these two variables in the CCD study. These models, represented as contour diagrams, show that an oxide coating with a Ra value of 1.5 μm exhibited the maximum corrosion resistance.