Effect of T6 Heat Treatment on Corrosion of Al-SiC p Composite & Inhibition Evaluation of Benzimidazole & Its Derivatives

Abstract

Aluminium alloys, particularly 6061, reinforced with SiC have been the focus of the attention because of their application potential in an extensive range of demanding applications, such as automobiles, aerospace, and defense. There are many other applications which involve exposure of the composites to the potential corrosive environment. Because of the duplex nature of the composites, they are prone to accelerated corrosion compared to their monolithic counterpart. Corrosion of these composites not only limit their service life but also lead to deterioration of their unique mechanical properties for which they are designed. Studies reveal the role of micro structural changes and processing routes on the corrosion behaviour. Also, aging treatment was found to have an influence on the corrosion rate as the heat treated samples showed higher corrosion rates as compared to the non-treated samples. Corrosion studies in organic acid solutions are rare in comparison with similar studies in mineral acids. Acetic acid is a frequently used organic acid in many industrial processes. At high temperatures, these acids dissociate, generating new aggressive ions which cause faster corrosion and they can provide sufficient protons to act as true acids. Adding inhibitors to the corrosion medium is a general practice for the corrosion protection. Heterocyclic organic compounds which contain oxygen, sulphur, phosphorous, nitrogen and aromatic rings are considered to be the most active and resourceful inhibitors in the acidic corrosive medium for the metals, alloys, and composites. Latterly, benzimidazole and its derivatives have established a considerable reputation on their corrosion inhibition properties for metals and alloys, owing to the existence of aromatic rings and nitrogen atom. In the present study benzimidazole (BI), 2-methylbenzimidazole (2-CH3-BI), and 2- mercaptobenzimidazole (2-SH-BI) are used as inhibitors. Aging profile of T4 and T6 treated Al-SiCp was obtained using Rockwell B hardness. Under-aging, peak-aging, and over-aging temperatures and time were found out. Samples were corrosion tested and found to be susceptible to corrosion in acetic acid where peak-aged samples exhibited higher corrosion and over-aged samples8 showed minimum corrosion. Three inhibitors were tested for their efficiency. Results proved that they are excellent inhibitors. The maximum inhibition efficiency obtained using BI was 66%, 69% offered by 2-CH3-BI and 75% was achieved in the presence of 2-SH-BI. Inhibition efficiency of inhibitors followed the order of 2-SH-BI > 2- CH3-BI > BI. Activation energy, enthalpy, entropy, and free energy of adsorption were calculated for all experimental conditions. Results suggest that inhibitors get adsorbed on the composite surface by mixed adsorption, where chemisorption is predominant.