Papers by Author: K.Y. Nam

Abstract: Mg is one of the most promising structural materials for lightweight applications due to its low density, good castability and damping capacity. In this study, we investigated the effect of silver (Ag) addition on alloy ageing behavior and mechanical properties of Mg-Al-Si-Sn-Sr-Ag alloys with variation of Ag contents (0.1, 0.5, 1.0, 2.0wt%). The ageing kinetics of Ag added alloys was determined and affected by Ag addition. Although the precipitation of platelets of Mg17Al12 within α-Mg matrix was not significantly affected by the silver, mechanical properties such as hardness and tensile properties were improved with increasing Ag contents.

Abstract: The effects of tin (Sn) and strontium (Sr) additions on the microstructure and creep properties of Mg-5Al-2Si (AS52) alloys were investigated. Results showed that the addition of Sn did not affect the morphology of secondary phase Mg2Si particles but induced the fine and uniform precipitation of thermally stable Mg2Sn at the grain boundary in the AS52 alloys. However, the morphology modification of the secondary phase Mg2Si particles from Chinese script shape to refined polygonal shape was greatly affected by the addition of Sr. Tensile strength and creep resistance were improved and tensile elongation was also increased in the modified alloy with addition of both Sr and Sn. Sn is the effective element for precipitating thermally stable Mg2Sn finely and uniformly at the grain boundary and Sr is the effective element for refining microstructure. Therefore both Sn and Sr are effective for modifying the microstructure and improving the creep properties of AS52 alloys.

Abstract: The effect of Al content on the castability, tensile and creep properties of Mg-xAl-Zn alloy was investigated. The molten Mg-(3~11)Al-Zn alloys of 700 °C were poured into the mould designed to estimate castability. Tensile and creep tests were performed for the alloys. It has been shown that creep resistance decreased while tensile strength improved with increasing Al amount. Microstructure study revealed that morphology of Mg17Al12 is main factor determining the tensile and creep properties of as cast Mg-xAl-Zn alloys. The final purpose of this study is to develop the heat resistant Mg alloys to apply transportation systems such as automobile. Further study on effect of heat treatment and additional alloying elements on the microstructure and mechanical properties of Mg-xAl alloys is going to be performed.

Abstract: A study has been made on the effects of antimony (Sb) and strontium (Sr) additions on the microstructure of Mg-Al-Si alloys. Results showed that the additions of Sb and Sr can modify the morphology of Mg2Si particles from Chinese script shape to refined polygonal shape. Tensile strength and creep resistance were improved and tensile elongation was also increased in the modified alloy with Sb and Sr. The addition of Sr was more effective than Sb modification of AS52 alloy for refining microstructure and thus improving properties.

Abstract: The effect of Al content on the castability, tensile and creep properties of Mg-xAl-Zn alloy was investigated. The molten Mg-(3~11)Al-Zn alloys of 700°C were poured into the mould designed to estimate castability. Tensile and creep tests were performed for the alloys. The results show that the castability increased with higher Al content. Creep resistance decreased while tensile strength improved with increasing Al amount. Our microstructure study revealed that morphology of Mg17Al12 is the main factor determining the tensile and creep properties of as cast Mg-xAl-Zn alloys. The final purpose of this study is to develop the heat resistant Mg alloys to be applied in transportation systems such as automobile. Further research will be conductedon the effect of heat treatment and additional alloying elements on the microstructure and properties of Mg-xAl alloys.

Abstract: The effects of antimony (Sb) and strontium (Sr) additions on the microstructure of Mg-Al-Si alloys were studied. The results show that the additions of Sb and Sr can modify the Mg2Si particles from Chinese script shape to refined polygonal shape. Tensile strength and creep resistance are improved, and tensile elongation is also increased in the modified alloy. Sr modification is more effective than Sb modification of AS52 alloy for refining the microstructure and thus improving its properties.