In the present work, the corrosion properties of Mg-xSn-5Al-1Zn (x ¼ 0, 1, 5 and 9 mass%) alloys have been investigated. Potentiodynamic polarization and immersion tests were carried out in 3.5% NaCl solution of pH 7.2 at room temperature to measure the corrosion properties of Mg-xSn-5Al-1Zn (x ¼ 0, 1, 5, and 9 mass%) alloys. Microstrucral analysis shows the Mg 17 Al 12 and Mg 2 Sn phase were mainly precipitated along grain boundaries. With increase of the Sn contents, the volume fraction of the secondary phases, i.e. Mg 17 Al 12 and Mg 2 Sn phase, was increased. The corrosion resistance of Mg-xSn-5Al-1Zn alloys was improved by the Sn addition. Especially, the AZ51-5 mass%Sn alloy characterized the superior corrosion resistance in the studied alloys. It seems that the presence of Sn stabilized the Mg(OH) 2 layers on the surface of Mg alloys and the secondary phases effectively formed semi-continuous structures, resulting in a drastic improvement of corrosion resistance of the Mg alloys.
The effects of Yb addition on the microstructure and mechanical properties of Mg-5Al alloy are investigated. The results indicate that the addition of Yb to the Mg-5Al alloy facilitates the formation of a thermally stable Al 2 Yb phase, the refinement of the microstructure and the suppression of the volume fraction of Mg 17 Al 12 phase in Mg-5Al alloy. Yb addition has little effect on the mechanical properties of the experimental alloys tested at room temperature. At elevated temperatures, however, the ultimate tensile strength (UTS) is significantly increased by Yb addition and Mg-5Al-1Yb has the highest UTS value than other experimental alloys. On the other hand, the yield strength (YS) increases at all tested temperatures due to the grain refinement and dispersion strengthening of the secondary phase. Meanwhile, the elongation (") of the experimental alloys decreases at all tested temperatures. Tensile fractographic analysis indicates that cleavage fracture is the dominant mechanism of the Mg-5Al and Mg-5Al-xYb alloys at room temperature. At elevated temperatures, however, the fracture mechanism of experimental alloys mainly changes from cleavage to quasi-cleavage fracture.
The development of new creep resistant magnesium alloys has become a major research focus. This study examined the microstructure and creep properties of Mg-4.0 mass%Al-2.0 mass% Sn-1.0 mass%Ca alloys containing Ce. The results showed that Ce could improve dramatically the tensile strength and ductility of the alloy at room temperature and increase the creep resistance at elevated temperatures significantly. With a trace amount of Ce, the morphology changed from a coarse CaMgSn phase to a refined shape and the microstructure of the alloy was remarkably refined.
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