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.

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Currently most commercial magnesium alloys are based on the Mg-Al system and it is reasonably well developed. Although the Mg-Al based alloy system has excellent castability and adequate ambient temperature mechanical properties, it shows poor creep resistance. Therefore, our group has focused on finding the way to improve the creep properties of Mg alloys. This paper presents a brief summary of the research achievements in this area recently made by AFML(Advance Functional Materials Lab in PNU, Korea). The properties of newly designed Mg alloys in our group are presented and compared with the properties of commercial A356 alloy.