Exploration of the effect of Zn-MgO-UPP coating on hardness, corrosion resistance and microstructure properties of mild steel

This paper investigated the effect of unripe plantain peel (UPP) nanoparticles reinforced Zn-MgO composite coating on the hardness, anti-corrosion and microstructure properties of mild steel. The anti-corrosion characteristics of the coatings were examined using the potentiodynamic polarization method, employing 3.65 % NaCl solution as the test medium. The hardness of the coatings was studied employing the Brinell hardness technique, while the microstructure characteristics were examined using XRD and SEM/EDS. The results of the study revealed that the as-received mild steel sample exhibited the corrosion rate and hardness value of 8.6272 mm year-1 and 136.8 kgf mm-2, respectively, while the Zn-MgO coated mild steel sample exhibited a corrosion rate and hardness value of 242.5 kgf mm-2 and 3.6362 mm year-1, respectively. The optimal performing Zn-MgO-UPP coated mild steel sample (sample coated with 20 g L-1 of MgO and 6 g L-1 of UPP) exhibited a corrosion rate and hardness value of 0.8317 mm year-1 and 245.8 kgf mm-2, respectively. The corrosion rate and hardness value of the Zn-20MgO-6UPP coated mild steel sample indicated that the UPP nanoparticles further improved the passivating and strengthening ability of Zn-MgO coating. Moreover, the XRD profile of the coatings possessed high intensities, which indi­cat­ed that the coatings exhibit microstructural and chemical homogeneity, high stability and good texture. It was observed on the SEM micrographs that the Zn-MgO-UPP coating exhi­bited a more refined microstructure compared to the Zn-MgO coating, indicating the grain refining tendency of the UPP nanoparticles. The EDS further indicated the presence of essential and dispersion strengthening elements in the coatings.