The effect of changing the type of surfactant as an electrolyte additive in the hard anodizing of aluminum alloy 2024

Today, due to the large use of aluminum alloys, it is tried to be protected against corrosion. Each alloy has a special feature that is used in a specific industry. Aluminum 2xxx is one of these alloys., which is rich in copper [1]. The presence of copper causes cracking and reduces corrosion resistance by creating oxides. Naturally formed oxide film on the surface of aluminum reduces corrosion rate to significant extent, but this layer may not be able to fully protect aluminum from corrosion due to the presence of corrosive agents [2]. aluminum can be electrochemically oxidized in an aqueous solution to form an oxide layer that is thicker than the native one.1 This phenomenon has been called “anodization” because the aluminum part to be processed constitutes the anode in an electrolytic cell. Anodizing current, applied potential or current, time as well as the type of electrolyte and its concentration are factors affecting the oxide layer [3]. The change in the type of electrolyte has a great effect on the oxide layer. One of these additives is alcohol such as ethylene glycol. alcohol functions as an antifreeze agent in the electrolyte; the alcohol acts as a cooling agent; and the alcohol prevents non-uniform growth of the anodic film (i.e., burning) even at a relatively high current density or voltage [4]. Another of these additives is the use of anionic surfactant. When aluminum is anodized, it exhibits positive charge on its surface and is attracted by an anionic surfactant on the surface of nano-porous aluminum oxide. As a result, the absorbed surfactant prevents the surface from dissolution thus leads to longer pore channel length [5]. Surfactants include ionic and non-ionic types, where the ionic type includes anionic and cationic. They are different from each other in their head or tail group and a change in it can cause a change in their properties [6]. In the present study, an attempt was made to study the effect of changing the type of surfactant in the presence of Ethylene Glycol (EG) on anodizing. For this purpose, hard anodizing was performed on 2024-T3 at -2°C for 1 h and 55 V. A combination of 2 M Sulfuric Acid (SA 2M) and ethylene glycol 10% v/v (EG 10%) was used as electrolyte. Once, half CMC of SDS surfactant and half CMC of SDBS surfactant were added to this solution in two separate samples and then under the mentioned conditions of hard anodizing. Both SDS and SDBS have a ten-carbon chain, but SDBS has a benzene ring in its head group.