ABSTRACT
The aim of this study was to investigate the properties of an electroless Ni-P-Al2O3-Mo2C coating on a 90wt% Al-10wt% Mg alloy. A thermal process was conducted at 400 °C for 1 hour to assess the impact of temperature on the coating properties. The structure of the bilayer coatings was analyzed using X-ray diffraction (XRD), and the surface topography of the hybrid coating was observed using a scanning electron microscope. It was found that at a concentration of 2 g/L, the Al2O3 and Mo2C distributions in the Ni-P coating bath exhibited a more uniform nodular or columnar structure. The hardness of the deposit was measured using a Vickers hardness tester, and the Ni-P-Al2O3-Mo2C coating sintered with a nanoparticle concentration of 2 g/L showed the highest hardness value of 692 VHN. This value was 19.32% higher than the unsintered Ni-P-Al2O3-Mo2C external layered coating. Furthermore, potentiodynamic polarization studies were performed in a 3.5% NaCl solution to evaluate the corrosion behavior of the hybrid coating under ambient conditions. The results indicated that the Ni-P-Al2O3-Mo2C coating formed at 2 g/L provided the highest corrosion protection, as confirmed by the highest positive Ecorr value of -0.2.4 V, attributed to the maximum particle deposition rate. Overall, the combination of NiP3, Al2O3, and Mo2C phases in the coating exhibited synergistic effects, leading to improved anti-corrosion and mechanical properties.
KEYWORDS: Electroless Ni-P coating, Heat treatment, Microhardness, Corrosion resistance, Hybrid coatings
2024 – Egyptian Journal of Chemistry