Effect of Thiourea on Electrodeposited Co–Mg–Nd Alloy Coating in Deep Eutectic Solvents

Abstract

Potentiostatic technique was used to investigate the effect of additive thiourea on the deposition mechanism of Co2+ in choline chloride–urea eutectic solvent system. The Co–Mg–Nd ternary alloy coating was prepared by linear scanning technique which was used to study the electrochemical behavior of Co2+, Mg2+ and Nd3+ in the system and the corrosion resistance of alloy coatings. The results show that Co2+ follows the growth mechanism of three-dimensional continuous nucleation in choline chloride–urea eutectic system. When the amount of thiourea added exceeds 300 mg, the nucleation mode of Co2+ approaches the three-dimensional instantaneous nucleation. The cathodic polarization curves of Co2+, Mg2+, and Nd3+ in the choline chloride–urea system shows a trend of weakening first and then increasing with the increase of thiourea content. At the addition of 100 mg, the cathodic polarization of the films was the strongest, which was conducive to deposite. According to the Ecorr and Icorr obtained by tafel curve, it is found that adding thiourea in the plating solution system could change the corrosion resistance of the coating. When the content was less than 100 mg, the corrosion resistance of the coating is the best. With the thiourea content increasing, the corrosion resistance of the coating is gradually weakening. It is found that the plating solution with 100 mg thiourea added can prepare Co–Mg–Nd ternary alloy coating with excellent coating morphology, high rare earth content and stable compound, by SEM, EDX and XRD analysis.