One of the corrosion mitigation methods that is used for the protection of steel operating in seawater environments involves the application of sacrificial metallic coatings (such as aluminium, zinc, and their alloys). This paper reviews current knowledge about thermally-sprayed (TS) and cold-sprayed (CS) Al coatings for the corrosion protection of steel. It also summarises the key findings of the substantial amount of work that has been devoted to understanding mechanisms and the parameters that control the performance of TS Al coatings, such as the spraying method and its parameters like coating thickness and the application of sealer. The paper includes suggestions for areas of further research that could lead to the development of more resilient and longer-lasting coatings, based on the results from both laboratory and field tests that have been published in the literature. It also highlights the need for conducting simulated laboratory tests at conditions of intended service and the importance of long-term testing.
In this work, the behaviour of arc-sprayed aluminium (1050) coatings was investigated under full artificial seawater immersion and compared with simulated splash zone conditions under droplets of artificial seawater exposed to controlled conditions. To gain a better insight into the mechanism of corrosion of thermally sprayed coatings, tests were also performed on solid 1050 aluminium. Effectiveness of TSA coatings was evaluated using electrochemical techniques and corrosion products were examined by SEM/EDX and Raman spectroscopy.Sulphur containing corrosion products, such as felsobanyaite, were found on the coating as well as on the solid metal. This highlights the importance of using seawater, and not NaCl solutions, as a corrosive medium simulating marine environment. Moreover, it was observed that cathodic and anodic regions on thermally sprayed coatings were not easily distinguishable, whereas on solid metal, cathodic areas were located in the spreading region, where carbonate corrosion product (dawsonite) was detected. Full immersion studies revealed the need for pre-exposing samples before electrochemical testing, to predict long-term behaviour of the coating in marine service.
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