Taguchi optimization of PEO process parameters for corrosion protection of AA7075 alloy

In this study, oxide coatings were grown by plasma electrolytic oxidation (PEO) process to enhance the corrosion resistance of the AA7075 alloys. The effect of process parameters on the corrosion resistance of PEO-treated AA7075 alloys was investigated systematically by the Taguchi analysis method the means of the three-level effects of four factors (current density, frequency, duty cycle, and electrolyte concentration). Grazing angle X-ray diffraction (GAXRD) has been used to determine phases on the surfaces. The surface morphology, thickness, pore diameter, and elemental analysis of the coatings were characterized with scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The corrosion behaviour of the PEO coatings was investigated using the potentiodynamic polarization scanning (PDS) technique in 3.5% NaCl solutions at room temperature. According to the signal-to-noise (S/N) ratio, optimum parameter/level combinations were determined for the best corrosion resistance. The percentage contribution of each parameter was determined by the analysis of variance (ANOVA). The results showed that frequency is the most significant parameter affecting the corrosion resistance of the PEO coatings. On the other hand, the highest polarization resistance of 2332 × 103 Ω cm2, 476 times better than the uncoated AA7075 substrate, was achieved in the confirmation run grown under optimum conditions.