Ni-Co / nano-Al2O3 composite coat was electrodeposited from environmentally friendly citrate tub. The electrodeposition was established from agitated solutions, containing disparate amounts of nano-Al2O3 particles. The addition of nano -Al2O3 to the plating solution decreases the polarization for Ni-Co alloy plating. The quantity of Al2O3 in the composite rises with concentration of Al2O3 in the coating solution, current density and decreasing temperature. Composites were examined by scanning

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... ectron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive Xray (EDX) techniques. The obtained composites were crystalline and had face-centered cubic (FCC) structure. The thickness of composite diminishes with increasing the amount of Al2O3 in the composite however, the microhardness increases. The resistance of Ni-Co / nano-Al2O3 composite against corrosion in 3.5 % salt water was tested by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Ni-Co / nano-Al2O3 composites had a good corrosion resistance. There is a growing demand to ameliorate Metal Matrix Composites coatings (MMCs). Advances in technology need materials with particular properties. In general, composites possess topnotch characteristics such as eminent hardness, acceptable resistance to corrosion at higher temperatures, surpass wear and oxidation resistances. In addition to electrical and magnetic properties, self-lubrication, tensile and breakage strength, high thermal stability, chemical and biological compatibility relative to conventional pure metal or metallic alloy composites [1] [2] [3] . Nano-particles show various specific physical & chemical properties due to quantum size and quantum tunnel effects. Nano-composites plating technique, in which nanoparticles are inserted into to metallic composites, to enhance their physical & mechanical properties, illustrates how nanotechnology can be utilized for plating of composites. Composites can be obtained by a variety of techniques such as thermal spraying, plasma spraying, chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless deposition and electrodeposition [4] [5] [6] . Among these techniques electrodeposition technique has proved itself to be a promising technique to produce metal matrix composites in a single step. It produces harder and smoother surfaces. This enhances bonding among codeposited molecules and metal and allows fine control for the coating thickness [7 & 8]. Electrodeposited MMCs fundamentally composed of elastic metal / alloy matrix in which another fine indissoluble inert phase with a diversified particle size, ranges from micrometric and submicrometric to nano-metric one, is distributed [9 &10]. The particle size has a pronounced effect on the properties of the coating. In chief, the properties of the coat were improved greatly as the particle size of codeposited particles decreases [11] . In the last few years, a variety of nano-sized particles ranging from 4 -800 nanometers have been incorporated successfully into metallic composites. Currently, there is a growing trend to use particles less than 100 nanometers to obtain a new innovative of advanced materials [12 &13]. The particles that used in composites were categorized into 2 important categories: soft & hard particles. Soft particles act as self-lubricant substances to minify friction between sliding surfaces. On the other hand, hard particles such as SiO2, Al2O3, SiC, and Si3N4 amend the mechanical properties and microhardness of deposited metals and alloys [14] [15] [16] [17] . Ceramics in the form of oxides are inorganic compounds of metallic (Al, Ti, Cr) or metalloid (Si) elements with oxygen. They have the ability form a variety of composites with different metallic matrixes. They are utilized to increase the oxidation resistance, hardness and wear improvement over conventional composites. Several oxides such as alumina (Al2O3), silica (SiO2), chromia (Cr2O3), ferric oxide (Fe2O3), zirconia (ZrO2), ceria (CeO2), titania (TiO2), yttria (Y2O3), Dysprosium oxide (Dy2O3) and lanthana (La2O3) form different composites with various metallic matrixes [17] [18] [19] [20] [21] [22] [23] [24] . Alumina particles are one of the most studied ceramic materials [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] . It has many unique properties such as great chemical stability, utmost elastic modulus, large thermal stability, high hardness and corrosion resistance [25] [26] [27] . Moreover, it is an electrically nonconducting substance [28] . Wu and coworkers [26] prepared Ni-Co/Al2O3 composites using codeposition of alloys and Al2O3 from sulfamate tub. They studied the effect of plating conditions on the amount of Al2O3 particles in Ni-Co alloys. Chang and his team [29] deposited Ni-Co/Al2O3 composite coating using