Volume 33, Issue 1-2

AA2024-Tx is one of the most common high-strength aluminium alloys used in the aerospace industry. This article reviews current understanding of the microstructure of sheet AA2024-T3 and chronicles the emergence of new compositions for constituent particles as well as reviews older literature to understand the source of the original compositions. The review goes on to summarise older and more recent studies on corrosion of AA2024-T3, drawing attention to areas of corrosion initiation and propagation. It pays particular attention to modern approaches to corrosion characterisation as obtained through microelectrochemical techniques and physicochemical characterisation, which provide statistical assessment of factors that contribute to corrosion of AA2024. These approaches are also relevant to other alloys.

Coating for corrosion protection was popular during the past decade. Thermal spray coating played an important role during that time. In recent years, arc thermal metal spray coating became widely used. Arc thermal metal spraying method (ATMSM) provides proven long-term protective coating systems using zinc, aluminum, and their alloys for steel work in a marine environment. This paper provides a review of the latest development in ATMSM by evaluating the current techniques in the industry and by analyzing technical data obtained from an extensive experimental program.

High velocity oxyfuel (HVOF) spraying process is commonly used to produce superalloy coatings. The coating of engineering components is required to increase the service life and to obtain a combination of properties that are not possible from wrought alloys. The major shortcoming of the HVOF spraying process is that it produces heterogeneities in the coating microstructure. These heterogeneities may cause initiation and progression of the corrosion, causing the malfunction of engineering components. In this study, corrosion testing of the HVOF-sprayed Inconel 625 coating was carried out by direct current polarization and alternating current impedance spectroscopy to see how microstructural heterogeneities contribute in changing electrochemical response. Furthermore, the air-formed and potentiostatically grown passive oxide layers were analyzed by X-ray photoelectron spectroscopy (XPS) to study oxide growth as a function of applied potential. The bulk Inconel 625 was used as a reference alloy to compare the experimental results of HVOF coating. It is established from our results that the oxide layer formed on bulk alloy is uniform as compared with the one formed at HVOF-sprayed coating samples. The passive current density for the bulk alloy sample was 3.61±0.51 and 34.26± 8.34 μA cm -2 for the coated sample. The charge transfer resistance for bulk sample was 1.80×10 4 and 1.70×10 3 Ω cm -2 for the coated sample after passivation. The analysis of the passive layer by XPS also revealed that the oxide layer on bulk alloy is more consistent and protective than coating.

The corrosion inhibition and adsorption behavior of some novel Schiff bases based on amino acids on carbon steel in CO 2 -saturated 3.5% NaCl solution at 50°C was investigated using gravimetric, potentiodynamic polarization, linear polarization resistance corrosion rate, and scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy analysis (EDAX) techniques. Results show that the inhibition efficiency increases when the inhibitor concentration increases. Potentiodynamic polarization curves reveal that the used Schiff bases are mixed-type inhibitors. Experimental data indicate that these Schiff base inhibitors adsorb at the carbon steel/solution interface according the Langmuir adsorption isotherm. SEM/EDAX was used to examine the surface morphology of carbon steel samples in the absence and presence of the inhibitors. Quantum chemical calculations were further applied to explain the experimental results.