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

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.