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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.

The numerous industrial application of mild steel despite its susceptibility to degradation on exposure to the environment has called for the continuous search for materials that can protect its surface from contaminants which could affect its inherent properties. This paper therefore examined the corrosion-resistance, hardness and microstructure properties of unripe plantain peel (UPP) nanoparticles reinforced Zn-ZnO-MgO composite coatings deposited on the surface of mild steel. The corrosion properties of the coated steel samples were investigated using the potentiodynamic polarization technique, utilizing simulated seawater (3.65% NaCl solution) as the test medium. The hardness of the coated steel samples was studied using the Brinell hardness method, while the microstructure properties were investigated using XRD and SEM/EDS. The as-received mild steel sample was observed to exhibit a hardness value and corrosion rate of 136.8 kgf/mm2 and 8.6272 mm/year, respectively, while the Zn-10ZnO-10MgO coated mild steel sample exhibited a hardness value and corrosion rate of 246.5 and 1.7698 mm/year, respectively. Relative to the other samples, the Zn-10ZnO-10MgO-6UPP coated mild steel (sample coated with 10 g/L of ZnO, 10 g/L of MgO and 6 g/L of UPP) exhibited a highest hardness value and lowest corrosion rate of 254.8 kgf/mm2 and 0.6645 mm/year, respectively. These corrosion rate and hardness values of the Zn-10ZnO-10MgO-6UPP coated mild steel sample showed that the unripe plantain peel nanoparticles further enhanced the strengthening and passivating ability of Zn-ZnO-MgO-UPP coating. The SEM micrographs revealed that the Zn-ZnO-MgO-UPP coating possessed a more refined microstructure relative to the Zn-ZnO-MgO coating, signifying the grain refining ability of the unripe plantain peel nanoparticles. The EDS additionally indicated the occurrence of crucial and dispersion strengthening elements in the coatings. The XRD profile of the coatings exhibited high intensities, which signified that the coatings have high stability, good texture with microstructural and chemical homogeneity.