Plating Al coating on high-strength steel in chloroaluminate ionic liquid under pulse current modes

Aluminum coating is a potential candidate for cadmium coating replacement due to its excellent corrosion resistance and nontoxicity. Among the fabrication methods of Al coating, plating Al via ionic liquids has drawn major attention of researchers because of the superiority of controllability, stability and low energy consumption. However, the evolution rules of plating aluminum on high-strength steel via pulse current modes at room temperature requires deeper investigation. In this work, pulse current density and pulse duty factor are regulated to reveal the plating patterns of Al on 300M high-strength steel in AlCl₃-EMIC (2:1 in mole) ionic liquid. It is found that higher current density can significantly facilitate the nucleation of Al grains and the compactness of morphology, while an enlarged pulse duty factor tends to result in more regular Al crystals. When the current density and the pulse duty factor are fixed at 20 mA cm⁻² and 80 %, the densest and most uniform aluminum coating is obtained. The component of Al coating is verified to be pure Al crystals with good adhesion and the plating process achieves a high current efficiency of 97.27 %. Under the protection of Al coating, the impedance and galvanic corrosion current density of 300M steel substrate are optimized by two orders of magnitude, and the corrosion current density is markedly decreased from 5.58 μA cm⁻² to 0.77 μA cm⁻².