Electrodeposition of purified aluminum coatings from dimethylsulfone–AlCl3 electrolytes with trimethylamine hydrochloride

Aluminum (Al) coatings have been electrodeposited from dimethylsulfone (DMSO2)–AlCl3 electrolytes, but the coatings usually contained trace amounts of chlorine (Cl) and sulfur (S) as impurities. Since these impurities make the coatings hard and brittle, and moreover may adversely affect the corrosion- and oxidation-resistances of the Al coatings, it would be desirable to decrease their contents in the Al coatings. Examination of the Al coatings electrodeposited from the electrolytes with the addition of various amounts of trimethylamine hydrochloride (TMA) revealed that the Cl and S contents of the Al coatings decreased with increasing concentration of TMA in the electrolyte. The addition of TMA also brought about changes in the surface morphology and crystal orientation of the Al coatings. Preferential adsorption of TMA on the surface of the Al deposit was inferred to be a cause of the exclusion of Cl and S from the Al coating. As a result of the decrease in Cl and S contents, the Al coatings were softened.