a b s t r a c tFilms of the Mg(OH) 2 /Mg-Al layered double hydroxide composite were formed on the combustionresistant magnesium alloy AMCa602 by steam coating and characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The corrosion-resistance performances of the films in a 5 wt% NaCl solution were investigated using electrochemical measurements. The corrosion current density of the sample that was steam-coated at 433 K for 6 h using the aqueous solution containing 200 mM Al(NO 3 ) 3 decreased significantly more than that of the bare AMCa602. The correlations between the Mg-Al LDH content in the films, Al(NO 3 ) 3 concentration in the aqueous solutions, and corrosion current densities were investigated.
Corrosion resistant films were prepared on magnesium alloy AZ31 by steam coating using NaNO 3 aqueous solution as steam source. The chemical and corrosive resistant properties of the films were estimated using XRD, FT-IR, SEM, and electrochemical method. XRD patterns revealed that the film was composed of crystal Mg(OH) 2 and Mg-Al system layered double hydroxide (LDH), independent of treatment time. The film grew densely and uniformly with an increase in treatment time. Cross sectional SEM images revealed that the deposition rate was 8 µm/h. FT-IR spectra showed that the Mg-Al LDH had carbonate-ions and nitrate-ions in the interlayer. Potentiodynamic polarization curves of the film treated at 433 K for 7 h indicated that the corrosion current density decreased by more than four orders of magnitude as compared to that of the uncoated one. Immersion test in 5 mass% NaCl aqueous solution at 308 K for 168 h revealed that the chemical composition on the surface of the film treated at 433 K for 7 h changed hardly before and after the immersion test. These results indicates that the film coated AZ31 has a superior corrosive resistance.
An Mg(OH) 2 /carbon composite film was prepared on magnesium alloy AZ31 by an ascorbic acid (AA)-assisted hydrothermal method. All films were composed of crystalline brucite type Mg(OH) 2 . Film thickness decreased with an increase in the amount of AA added. X-ray photoelectron spectroscopy studies revealed that a peak component related to sp 2 -hybridized carbons contributed to improve film conductivity. Film resistivity decreased with an increase in C content. The film obtained from the aqueous solution containing 10 g/L of AA showed the lowest corrosion current density of all samples.
Effect of microstructure on corrosion resistance and heat resistance of flame-resistant Ca-added magnesium alloy AZ61 (AZX612) were investigated. An extruded and twin-rolled casting magnesium alloys AZX612 were used with a view to better understanding the relationship between microstructure and these properties. The microstructures of the magnesium alloys were characterized by optical microscope (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy dispersive X-ray spectroscopy (EDS). The shapes of compounds in the alloys observed by EDS were significantly different; spherical distribution in grain for the extruded magnesium alloy and preferential formation on grain boundaries for the twin-rolled casting magnesium alloy. The different microstructure of the two alloys resulted in showing the different properties. Immersion test in 5 mass% NaCl aqueous solution revealed that the corrosion rates for the extruded and twin-rolled casting magnesium alloys AZX612 were estimated to be 6.5 and 15.0 mm/year, respectively, indicating that the corrosion resistance of the extruded magnesium alloys AZX612 were more superior than that of the twin-rolled casting one. On the contrary, the heat resistance of the alloy did not change depending on the microstructure.
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