The alloy coatings such as zinc–nickel are used to improve the lifetime of zinc sacrificial coatings. zinc–nickel alloy coating has a longer history than other zinc alloy coatings and is considered as the most corrosion resistive zinc alloy. One of the important properties of this type of coatings is the ductility properties of coated steel pieces; as after thermal treatment and shaping operations, the corrosion resistance is enhanced up to an optimal level. Because of such properties, this alloy is investigated in coating the pieces such as connecting bolts, brake system components, and fuel system. Resistance to heat, ultraviolet light, hydraulic fluids, and fuels are other characteristics of such coatings. The use of zinc–nickel alloy coatings is growing in the bolts and threaded parts industry. Since these coatings do not prevent galvanic corrosion in contact with aluminum, they are widely used in industries that deal with aluminum bodies. However, the zinc–nickel alloys are considered as the most expensive coatings. These alloys are coated both by acidic and alkaline baths that provide different coating properties. This paper reviews the studies conducted on zinc–nickel alloy coatings, analyzing baths and their properties, the effect of different parameters on electrodeposition, as well as Zn–Ni multilayer and composite coatings and their properties.

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