Active Corrosion Protection by Epoxy Coating on Li2CO3-Pretreated Anodized Aluminum Alloy 2024-T3

The fast leaching and robust barrier property of inhibitors are the basic fundamentals for the formation of active protective coatings to protect aluminum alloys. Herein, an active protective surface was developed based on an epoxy coating and an underlying lithium carbonate (Li2CO3)-treated anodized aluminum alloy 2024-T3. The morphology of the Li-LDH layer was studied to know its formation mechanism. The electrochemical studies revealed that the fast and adequate leaching of lithium led to a substantial increment of corrosion resistance of the scratched coating in 3.5 wt% NaCl from 1 to 8 days. Time of flight secondary ion mass spectroscopy (ToF-SIMS) results indicated that Li was distributed in the lateral direction and covered the scratched area. The 3D images indicated that different lithium compounds were formed and 90% of the scratched area was covered with the lithium protective layer over immersion time. A combined approach of morphology observations, electrochemical measurements, and ToF-SIMS showed the lithium protective layer offered good corrosion resistance. On the contrary, lithium provided fast and adequate leaching from the coating, demonstrating good active protection for aluminum and its alloys.

Evaluation of Corrosion Inhibition Efficiency of Aluminum Alloy 2024 by Diaminostilbene and Azobenzene Schiff Bases in 1 M Hydrochloric Acid

The Schiff base compounds N,N ′ -bis(salicylidine)-4,4 ′ –diaminostilbene(SDS) and N,N ′ -bis(salicylidine)-4,4 ′ -diamino azobenzene(SDA) were synthesized, and their molecular structure was determined by FT-IR and 1H NMR. The corrosion inhibitions of Schiff base compounds on aluminum alloy 2024 in 1 M hydrochloric acid were evaluated by potentiodynamic polarization, impedance techniques, weight loss method, and scanning electron microscopic technique. The potentiodynamic polarization (PDP) studies revealed that SDS and SDA compounds acted predominantly as cathodic inhibitors. The electrochemical impedance spectroscopic (EIS) parameters confirmed the adsorption of SDS and SDA molecules over the surface of aluminum alloy 2024 alloy by forming an inhibitive layer. The weight loss studies showed that the inhibition efficiency of these compounds increases directly with concentration and decreases with an increase in solution temperature and immersion time. The thermodynamic parameters were calculated to investigate the mechanism of corrosion inhibition. The SDA was found to be more effective than SDS and followed the Langmuir adsorption isotherm model. The scanning electron microscopy (SEM) results revealed that the deterioration of the alloy surface is minimal in the presence of an inhibitor. Both Schiff base molecules exhibited superior corrosion inhibition for aluminum alloy 2024 alloy in HCl medium.

Developing a Benzimidazole-Silica-Based Hybrid Sol–Gel Coating with Significant Corrosion Protection on Aluminum Alloys 2024-T3

The inherent reactivity of Al–Cu–Mg alloys is such that their use for building structural, maritime, and airplane components with great strength/weight ratios would not be possible without good anti-corrosion systems. These systems could be considered as imitations of the protection mechanism found in the conventional hexavalent chromium-based system, but with additional limited environmental impact, and in particular without toxic or carcinogenic effects. These coatings also are intended to be eco-friendly, using less of the valuable raw materials and energy than more traditional methods. Silica-based hybrid protective coatings have been shown to exhibit excellent chemical stability combined with the ability to reduce the corrosion of metal substrates. However, research shows that sol–gel has some limitations in terms of the period of the anti-corrosive properties. Therefore, this work reports the performance of a silica-based hybrid sol–gel coating encapsulated with benzimidazole (BZI) that can be applied to light alloys to form an inherently inhibited and crack-free coating. This coating was applied on AA 2024-T3 and cured at 80 °C. The high corrosion resistance performance results from the combination of good adhesion, the hydrophobic property of the silica-based hybrid coating, and the presence of the encapsulated (BZI) film-forming volatile corrosion inhibitor, which is released at pores within the coating system, resulting in film-forming, reducing the reaction at cathodic sites. The evaluation of this mechanism is based on using electrochemical testing techniques. The anti-corrosion properties of the coatings were studied when immersed in 3.5% NaCl by using electrochemical impedance spectroscopy (EIS) and potential-dynamic polarization scanning (PDPS). The chemical confirmation was performed by infrared spectroscopy (ATR-FTIR), supported by analyzing the morphology of the surface before and after the immersion testing by using scanning electron microscopy (SEM). The benzimidazole-silica-based hybrid coating exhibited excellent anti-corrosion properties, providing an adherent protective film on the aluminum alloy 2024-T3 samples compared to sol–gel-only and bare metals, as a cost-effective and eco-friendly system.

Electrochemical Impedance Spectroscopy Behavior of Aluminum Alloys 2024 and 6061 in Rainwater

In the present work the electrochemical resistance spectroscopy behavior of aluminum alloy 2024 and 6061 in rainwater, was studied before and after solution heat treatment at room temperature (25 ° C). If the resistance decreases, the corrosion becomes faster, and vice versa. The equivalent circuits was of type Constant Phase Element (CPE) and the highest resistance value gets for alloy 2024 aged at 250 ° C for 2 hours, and the highest resistance value was for alloy 6061 aged at 250 ° C for 1 hour. As for the values ​​of capacitance, the highest amplitude value was for alloy 2024 aged at 300 ° C for two hours, and the highest value gets for capacity for alloy 6061 aged at 150 ° C for two hours.