The mechanisms of corrosion inhibition of AA2024-T3 by vanadates were studied using chronoamperometry, polarization curves and adsorption isotherms. The electrochemical behaviour of clear solutions containing metavanadates and orange solutions containing decavanadates was clearly distinctive. Metavanadates reduced the kinetics of oxygen reduction to an extent similar to chromates. Corrosion inhibition of AA2024-T3 by metavanadates was very rapid and it might occur by the formation of an adsorbed layer. Reduction of clear metavanadate solution was very slow. Approximately 35 min were required to develop a monolayer of a reduced vanadate species. The adsorption of the inhibitor likely blocked reactive sites on intermetallic particles, discouraging the oxygen reduction reaction (ORR). Adsorption of the inhibitor on the Al matrix could also displace Cl -ions, increasing the stability of the passive film and reducing the breakdown of S-phase particles. In contrast, decavanadates were shown to be poor inhibitors of the ORR. A sharp current spike was observed after injection of decavanadates for both Cu and AA2024-T3 at various applied cathodic potentials. Integration of the current peaks suggested the formation of several monolayers of a reduced vanadate species. The formation of several monolayers was in line with the poor performance of decavanadates as inhibitors of AA2024-T3 corrosion.

The inhibition of Al alloy corrosion by vanadates was studied in this work. Vanadium speciation is very complicated and vital to the inhibition efficacy. Critical conditions for decavanadate polymerization from clear metavanadate solutions were investigated. Decavanadate only formed when metavanadate was added to solutions of pH 3 or less. It was not possible to change the pH of a metavanadate solution without forming decavanadates, creating an orange-colored solution. According to 51 V nuclear magnetic resonance, monovanadates were present only in clear metavanadate solutions; orange solutions always contained decavanadates and never contained monovanadates. Orange decavanadate solutions containing 0.5 M NaCl at pH 8.71 exhibited no significant inhibition of the oxygen reduction reaction and increasing decavanadate concentration was detrimental. In contrast, clear metavanadate solutions containing monovanadate exhibited strong inhibition of the oxygen reduction reaction, to a level similar to chromate. At a fixed pH, increased NaVO 3 concentration in clear metavanadate solutions increased inhibition efficiency.High-strength aluminum alloys are used widely in structural aircraft applications because of the combination of good mechanical properties and light weight.

The mechanisms of corrosion inhibition of AA2024-T3 by vanadates were studied in this work using the split cell technique and polarization curves. The electrochemical behavior of clear solutions containing metavanadates and orange solutions containing decavanadates was clearly distinctive. Injection of metavanadates to the cathode side of the different split cell setups greatly reduced the galvanic current, indicating a potent inhibition of the oxygen reduction kinetics. The galvanic current never exhibited a transient current peak, suggesting that metavanadates inhibit AA2024-T3 corrosion by a mechanism that does not involve electrochemical reduction. Injection of metavanadate to the anode side of the different split cells had no effect on the galvanic current. Injection of orange decavanadate to the cathode side of the AA2024-T3 split cell resulted in a large current peak, associated with the electrochemical reduction of decavanadate. However, decavanadates did not impart significant corrosion protection.

Magnesium and magnesium alloys are susceptible to stress corrosion cracking in various environments, including distilled water. There is compelling evidence to conclude that SCC is assisted, at least in part, by hydrogen embrittlement. This paper reviews the thermodynamics of the Mg-H system and the kinetics of hydrogen transport. Aspects of magnesium corrosion relevant to hydrogen absorption are also discussed. Crack growth mechanisms based on delayed hydride cracking, hydrogen adsorption dislocation emission, hydrogen enhanced decohesion, and hydrogen enhanced localized plasticity have been proposed and evidence for each of them is reviewed herein.

The morphology and kinetics of the localized corrosion of aluminum alloy (AA)2024-T3 (UNS A92024) at the open-circuit potential were investigated by in situ atomic force microscopy (AFM) scratching. The addition of metavanadate to chloride solutions resulted in outstanding corrosion inhibition. Samples exposed to 0.1 M sodium chloride (NaCl) with no inhibitor developed a trench-like attack at the periphery of large Al-Cu-Fe-Mn-(Si) intermetallic phases. The addition of dilute metavanadate markedly reduced the kinetics of the attack. In addition, most S-phase particles remained free of attack. Higher concentrations of metavanadate increased protection even further so that only high AFM tip forces could induce pitting corrosion. Corrosion attack was immediately observed when AA2024-T3 samples were exposed to chloride solutions containing orange decavanadates. The attack nucleated on the exposed surface but not under the AFM tip. The attack grew continuously, accompanied by gas evolution and formation of corrosion products. Optical inspection after the test indicated severe corrosion damage, confirming an overall poor performance of orange decavanadate solutions as corrosion inhibitors.