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The Al-Zn-Si coating was deposited on Q235 steel by thermal spray technology. The corrosion behaviour of the coating in simulated marine environments has been investigated through neutral salt spray test (NSS) and electrochemical test. Furthermore, the microstructure and the morphologies of the coating were detected by means of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The results showed that the coating exhibited a dense homogeneous lamellar microstructure without obvious defects. There were different corrosion periods of the coating in the simulated marine environment, such as dissolution of Zn and Al particles, flocculent morphology, acicular crystals and self-sealing behaviour caused by corrosion products. Ultimately, a dynamic equilibrium was formed between the consumption of the coating and the generation of the corrosion product layer. Moreover, Tafel curves indicated that the Ecorr and Icorr of the coating after NSS were lower than the substrate that had a sufficient driving force of the cathodic protection. [ABSTRACT FROM AUTHOR]

In order to improve corrosion resistance of pure titanium in strong acid solution, the tantalum modified layer was formed on the pure titanium surface by double glow plasma surface tantalumising. The modification layer was comprised of deposition layer and diffusion layer, which metallurgically adhered to the substrate. Tantalum element decreased with the case depth. The corrosion resistance of the tantalum modified layer in HCl solution was investigated by weight loss method and electrochemical measurements, and the corrosion morphology (SEM) was studied by SEM and X-ray diffraction. The annual corrosion rate of the modified layer was only 12 and 21% of pure titanium in 10 and 20 wt-% HCl solution respectively, and the corrosion rate was still small in 30% HCl solution. In concentrated acid for 120 h, it was found that there was significant pitting corrosion on the surface of pure titanium, while no pitting corrosion could be perceived in the modified layer. The main reason for the good corrosion resistance was a compact, stable tantalum oxidation film formed at the surface of the modified layer. [ABSTRACT FROM AUTHOR]