Effect of microstructure on corrosion resistance and heat resistance of flame-resistant Ca-added magnesium alloy AZ61

Abstract

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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“…Figure 1 shows the XRD and XPS results of the surface of the AZX612 before and after the anodic oxidization. Refering to the reports by Serizawa et al 18) and Yuasa et al, 19) peaks of Mg, Al 2 Ca, Mg 17 Al 12 , and AlMn compounds were observed in the both XRD patterns. It is considered that the unmarked peaks, which were not observed in the above references, were derived from some compounds generated by the manufacturing process of the untreated substrate.…”