Evolution and stability of 2-mercaptobenzimidazole inhibitor film upon Al alloy 6061

Abstract

Organic corrosion inhibitors have become competent alternatives to hazardous chrome conversion coatings due to their rapid adsorption over metal surfaces in corrosive environments. Literature suggests a wide range of organic corrosion inhibitors with high inhibition efficiency, barrier properties, and adsorption mechanisms. However, the long-term durability and protectiveness of an organic inhibitor film need to be understood with in-depth insights on its interaction with heterogenous alloy surfaces like AA6xxx, reduction of galvanic activities and time-resolved degradation due to ionic diffusion. The present article is focused on the time-resolved adsorption and degradation of 2-mercaptobenzimidazole (2-MBI)-induced inhibitor layer/film over AA6061 in 0.1 M NaCl solution. Electrochemical and surface analysis data indicate that the presence of 2-MBI drives the rapid formation of a 20–30 nm thick protective film comprised of constitutional elements of C, S, and N from 2-MBI upon the surface of AA6061 substrate. This film mitigated the corrosion cells associated with nano- and micro-sized Fe and Si-rich intermetallic particles (IMPs) in AA6061. XPS reveals two distinguished bonding states of S and N in the inhibitor film and chemical interactions between 2-MBI and the surface of AA6061. The protective film maintained 65% inhibiting efficiency after 1 day, which progressively degraded due to electrolyte ingress and eventually with a drop in inhibition efficiency down to 21% after 14 days. Inhibitor-induced film over AA6061 reduced the corrosion susceptibility of Fe, and Si-rich IMPs up to 1 day given the subsequent adsorption by S and N heteroatoms. However, this film became thick and defective after 1 day, which undermined its barrier properties against ingress of aggressive ions and facilitated water adsorption. Graphical abstract

Corrosion inhibitor screening for AA6014 aluminum alloy under different ambient conditions using a novel multielectrode methodology

“…The amphoteric nature of aluminium oxides under high pH conditions could degrade the oxide layers, exposing bulk Al to anodic dissolution. 42 The presence of chloride ions disrupts the stability of the passive layer, potentially reducing the passive range. Conversely, when the solution incorporates an effective inhibitor, it can expand the pH range beyond the typical stability thresholds of aluminium oxide.…”

“…For the alloy AA6014, it has been reported that Mg 2 Si acts as an anode due to the anodic corrosion potential of the Al matrix. 6,42 Consequently, these intermetallic particles preferentially dissolve concerning the Al matrix in neutral and acidic conditions. Fig.…”