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In the presented work, the possibility of direct synthesis of LDH (layered double hydroxide) on the AZ91 surface in the presence of a chelating agent (diethylenetriaminepentaacetic acid - DTPA) is reported. Conversion layer of LDH nanocontainers were formed under ambient pressure conditions without carbonate addition in the electrolyte. The obtained LDH was characterized using experimental (SEM, XRD, TGA, XPS, Raman, etc.) and computational methods (thermodynamic calculation, modeling of possible LDH crystal structures). A comparison of three possible LDHs (LDH-OH, -NO 3 and -CO 3) was performed. Based on the experimental results and crystal simulation approach, it was confirmed, that the mixed LDH-OH/CO 3 is grown on the surface in the presence of DTPA pentasodium salt. [ABSTRACT FROM AUTHOR]

Abstract: In this paper the interface of poly(vinylidene fluoride) coatings prepared by the dip coating method and HF-treated AZ31 magnesium alloy was evaluated. The best performance of this system in corrosion tests compared to ground, as-received and acetic acid cleaned substrates is related to an acid–base interaction at the interface and to interfacial reactions which resulted in a self-healing process. The protectiveness of the samples was investigated using impedance and immersion tests while the coating morphology and interface stability were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy and adhesion tests. [Copyright &y& Elsevier]

Abstract: In this study, investigations on the protectiveness of poly(ether imide) coatings against corrosion of magnesium AZ31 alloy sheets are performed. The coatings were prepared in different pre-treated substrates by the dip coating method using N′N′-dimethyl acetamide (DMAc) and N′-methyl pyrrolidone solutions. The optimal performance was obtained for hydrofluoric acid treated substrates coated using DMAc solution (coating thickness 13μm) which showed impedances in the order of 107 Ωcm2 even after more than 3300h of exposure to a 3.5wt.% NaCl solution. This high performance is associated to an acid–base interaction at the interface as observed by X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

AM50 magnesium alloy is treated by PEO process using four different electrolytes which are combination of K3PO4 and Na3PO4 plus two different hydroxides, i.e. KOH and NaOH. Basic properties of the electrolyte such as pH, conductivity and breakdown voltage were measured. Moreover, coatings were characterised by scanning electron microscopy for the surface morphology and cross sectional study, X-ray diffraction for determination of phase composition and electrochemical impedance spectroscopy (EIS) for evaluation of corrosion resistance. The results indicate that KOH solutions need higher breakdown voltage and result in higher thickness of coatings. The values of the latter parameters are in the range of 150–160 V and 14–17 μm respectively. While those of NaOH solutions are in the range of 106–116 V and 5–6 μm thick. The final results show that presence of KOH in the solutions leads to a better corrosion performance of the coating compared to NaOH. [ABSTRACT FROM AUTHOR]

The corrosion behaviour of an AZ31 magnesium alloy coated with plasma electrolytic oxidation (PEO), polymer and a combination of them was assessed by electrochemical impedance spectroscopy (EIS) in 0·1M NaCl solution. The polymer coating was applied on a just cleaned surface (without any special preparation) and also on PEO treated magnesium substrate. While the polymer coated and the mere PEO treated magnesium alloy specimens lasted less than 50 h in the EIS tests, the specimens with the duplex coating (PEO+polymer) successfully resisted 1000 h in the EIS tests without showing any degradation. The improved adhesion of the polymer coating in presence of the PEO layer and the effective sealing of the pores in the PEO coating with the polymer were responsible for the enhanced corrosion resistance. The synergistic beneficial effect of the duplex coatings on the corrosion behaviour was also witnessed in the salt spray tests. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, the effect of hydrofluoric acid (HF) treatment on the surface composition and corrosion behaviour of the magnesium alloy AZ 31 was investigated. The HF treatment of the samples was performed with various concentrations and at different treatment times. The samples surfaces were analysed by Fourier transform infrared spectroscopy, optical emission spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. The results showed the formation of hydroxides, oxides and compounds of the general formula Mg(OH) x F2− x on the samples surfaces, as well as variations on impurities concentrations. The process led to distinct surfaces, each having its specific corrosion resistance, which was evaluated by electrochemical impedance spectroscopy and potentio-dynamic polarization. The most improved corrosion protection was achieved using the concentrations of 14 and 20molL−1 and 24h of treatment time, resulting in corrosion rates 20 times lower than those of untreated samples. These two solutions also resulted in an improved corrosion protection for further polymeric coatings, showing that this treatment is an excellent pre-treatment for corrosion protective layers on magnesium alloys. [Copyright &y& Elsevier]

Abstract: In the present study, the potential of poly(ether imide) as corrosion protective coating for magnesium alloys was evaluated using the spin coating technique. The influence of different parameters on the coating properties was evaluated and the corrosion behaviour of the coatings was investigated using electrochemical impedance spectroscopy. The best corrosion protection was obtained preparing the coatings under N2 atmosphere, using 15wt.% solution in N′N′-dimethylacetamide (DMAc) which resulted in a coating of approximately 2μm thickness, with an initial impedance of 109 Ωcm2 and of 105 Ωcm2 after 240h of exposure to a 3.5% NaCl solution. [Copyright &y& Elsevier]

Abstract: The present investigation evaluates the commercially available class of poly(ether imides) for corrosion protection of Mg alloys. This class of polymer is used in a wide field of applications like automotive, aerospace, medicine and electronics where it shows beneficial properties. The coatings were applied by dipping to the metal surface as porous and non-porous layers. The corrosion resistance of the coatings and the degradation behaviour were investigated by electrochemical impedance spectroscopy (EIS) as well as under environmental conditions like salt-spray and climate test. Furthermore the resulting polymer coating was qualified by ATR-IR and IR-microscopy. Surprisingly the results indicate that the porous type of coating has lower degradation rate than the dense coating, which was related to hydrogen release without damaging the coating and the interface. [Copyright &y& Elsevier]

Abstract: In previous publications of the authors, good performance of poly(ether imide) as corrosion protective coatings for magnesium AZ31 alloy was reported. It was suggested that during the sample degradation magnesium hydroxide could react with the imide ring forming magnesium polyamate and polyamic acid, but this could not be experimentally confirmed. In the present letter, we confirm the occurrence of this reaction by infrared and X-ray photoelectron spectroscopy and discuss its influence in the corrosion behavior observed in electrochemical impedance spectroscopy tests. [ABSTRACT FROM AUTHOR]

Abstract: Organic acids were used to clean AZ31 magnesium alloy sheet and the effect of the cleaning processes on the surface condition and corrosion performance of the alloy was investigated. Organic acid cleanings reduced the surface impurities and enhanced the corrosion resistance. Removal of at least 4μm of the contaminated surface was required to reach corrosion rates less than 1mm/year in salt spray condition. Among the three organic acids examined, acetic acid is the best choice. Oxalic acid can be an alternative while citric acid is not suitable for cleaning AZ31 sheet, because of insufficient removal of iron impurities. [Copyright &y& Elsevier]

Abstract: Surface contaminants as a result of thermo-mechanical processing of magnesium alloys, e.g. sheet rolling, can have a negative effect on the corrosion resistance of magnesium alloys. Especially contaminants such as Fe, Ni and Cu, left on the surface of magnesium alloys result in the formation of micro-galvanic couples and can therefore increase corrosion attack on these alloys. Due to this influence they should be removed to obtain good corrosion resistance. In this study, the effect of inorganic acid pickling on the corrosion behaviour of a commercial AZ31 magnesium alloy sheet was investigated. Sulphuric, nitric and phosphoric acids of different concentrations were used to clean the alloy for various pickling times. The surface morphology, composition and phases were elucidated using scanning electron microscopy, X-ray fluorescence analysis, spark discharge-optical emission spectroscopy, energy dispersive X-ray spectroscopy and infrared spectroscopy. The effect of surface cleaning on the corrosion properties was studied using salt spray test and electrochemical impedance spectroscopy. The experimental results show that acid pickling reduces the surface impurities and therefore enhances the corrosion resistance of the alloy. The cleaning efficiency of the three acids used and the corrosion protection mechanisms were found to be remarkably different. Best corrosion results were obtained with nitric acid, followed closely by phosphoric acid. Only the sulphuric acid failed more or less when cleaning the AZ31 sheet. However, to obtain reasonable corrosion resistance at least 5μm of the surface of AZ31 magnesium alloy sheet have to be removed. [Copyright &y& Elsevier]