# Progress in Electrodeposition of Zinc and Zinc Nickel Alloys Using Ionic Liquids
## 5 Substrate Effect  
In recent years, research has focused on the development of lightweight metals and their alloys in applications such as aerospace. The wide spread use of lightweight metals such as magnesium, aluminium, and their alloys have been gaining significant attention owing to their lightweight, density, and so on. Additional properties that contribute to the lightweight metal alloys' versatility in the automotive, electronic, and aerospace industries include a high thermal conductivity, high dimensional stability, good electromagnetic shielding characteristics, high damping characteristics, good machinability, and easy recyclability. These properties make magnesium and aluminium alloys of particular interest to the automotive and aerospace industries, where the weight reduction provides a simple means to achieve higher fuel efficiencies without sacrificing structural strength. Despite their widespread use and valuable properties, these metals are reactive and corrode aggressively in a humid atmosphere and corrosive environment, such as marine, and in an aqueous environment containing anions such as chloride (Cl\({}^{-}\)), fluoride (F\({}^{-}\)), bromide (Br\({}^{-}\)), and sulphates (SO\({}_{4}\)2\({}^{-}\)). Alloying with metals such as manganese (Mn) and certain rare earth elements improves their corrosion resistance. However, these alloys are known to be susceptible to galvanic corrosion owing to the segregation of the constituents on one hand and the presence of a humid atmospheric or aqueous environment on the other. The possibility of galvanic corrosion arises when dissimilar metals are in electrical and electrolytic (salt solution, acids or alkalis) contact. The more active metal (lower electrode potential) is likely to undergo corrosion. Galvanic corrosion is influenced greatly by the difference of electrode potentials, ratio between the areas of anode and cathode, and electrical conductivity of the electrolyte. While techniques such as dissimilar material joining (DMJ) have been gaining significant attention owing to their multi-functional advantages, riveting (involving hole drilling) is considered to be the widely used technology in the automotive sector. However, the risksand costs associated with the hole making operations (drilling, stamping, and so on) are mostly from the galvanic corrosion problems [61]. Moreover, anions such as Cl\({}^{-}\), Br\({}^{-}\), I\({}^{-}\), and SO\({}^{2-}\)\({}_{4}\) promote local and generalized corrosion, and result in severe pitting in the metal losing its mechanical stability. To overcome these challenges, one of the most effective ways to prevent the substrate from corrosion is to provide a uniform, pore free metallic coating, which not only acts as a corrosion resistant coating in harsh environment, but also prevents it from physical damage with good adhesion [62]. However, there are certain challenges associated with the plating of Zn and Zn-Ni on substrates that are reactive in nature. For example, the extreme reactivity of magnesium shall inhibit good adhesion of the Zn and Zn-Ni deposit and result in peeling of the coating. Another challenge in the plating of such substrates is that the quality of the coating is affected by the formation of intermetallic species at the grain boundaries and the creation of non-uniform surface potential across the substrate. Therefore, the development of non-aqueous based systems for plating of such substrates shall not only eliminate the aggressive reactions observed in the case of acidic solutions, but also improve the quality of the Zn and Zn-Ni coatings, and improve the corrosion resistance of the components used for aerospace and automotive applications. Electrodeposition of Zn and Zn-Ni alloys on these substrates from ILs can be employed to protect the substrates from corrosion and hydrogen embrittlement (due to hydrogen generation in case of aqueous systems). [PERSON] et al. [63] studied the electrodeposition of Zn onto pure Mg substrate and Mg-alloys, AZ31 and AZ91, using two different types of ChCl-based ILs.