Up-Scaling and Stabilization of Processes for the Electrodeposition of Aluminum Alloys for Corrosion Protection

Abstract

Aluminum and its alloys have excellent properties (e.g. specific weight, corrosion resistance) that are beneficial for a wide range of industrial applications. By forming a natural oxide layer of a few nm thickness, these materials are able to protect themselves from the progression of corrosive attack. Unfortunately, this oxide layer limits the use of pure aluminum for cathodic corrosion protection. Adding the right alloying elements can help to prevent the formation of the oxide layer and thus self-passivation.Electrodeposition is an elegant and cost-efficient method to deposit thin films on substrates with complex shapes. The choice of the electrolyte, its composition and the deposition parameters allow the tuning of the layer properties. Electroplated aluminum materials open up the possibility of replacing environmentally hazardous materials such as cadmium. Aluminum cannot be electrodeposited from aqueous electrolytes due to its negative Nernst potential (-1.66 V vs. NHE). Non-aqueous media make this possible due to large electrochemical windows. However, they are often limited by expensive and highly flammable chemicals (e.g. SIGAL and REAL process). High investment costs for process and plant technology are the consequence. Ionic liquids (ILs) allow the deposition of reactive metals such as aluminum at room temperature. They have a very low vapor pressure and are non-flammable. In addition, they exhibit good solubility for numerous metal salts and lower differences in the deposition potentials of the metals.This paper discusses the use of imidazolium-based chloroaluminate ILs for the electrochemical deposition of aluminum alloys for cathodic corrosion protection of high-strength steel. As an essential part of upscaling IL-based processes, the use of multianodes, their limitations, and the use of additives to optimize the deposition process and the coating properties will be discussed.