Aluminum Barrel Plating on Steel Bolts Using Chloroaluminate Ionic Liquids

Abstract

Al electroplating using ionic liquids (ILs) has been extensively studied for various potential applications, including corrosion-resistant coatings. When Al electroplating is to be performed commercially for many small objects, adopting the barrel plating method is reasonable for improving productivity and reducing manufacturing costs. However, little is known about the barrel-plating conditions for the formation of Al coatings. In this study, the barrel plating conditions for forming Al coatings on steel bolts using ILs composed of 1-ethyl-3-methylimidazolium chloride (EMIC) and aluminum chloride (AlCl₃) were investigated. Hull cell tests showed that the IL with an AlCl₃/EMIC molar ratio of 1.2 has a higher covering power than the IL with a higher AlCl₃ ratio. Barrel plating using the IL with an AlCl₃ ratio of 1.2 enabled complete coverage of the bolt with the Al coating. The uniformity of the Al coating on the bolts was further improved by adjusting the rotation speed of the barrel. Furthermore, a simple pretreatment procedure for steel bolts was proposed to obtain an electrodeposited Al coat that adheres well to steel bolts.