Mg-X%Li계 합금의 미세조직 및 기계적 성질에 미치는 가공열처리의 영향

Abstract

Effect of Thermomechanical Treatment on Microstructure and Mechanical Property in Mg-X%Li Based Alloys

By Park Youn-Jae Advisor: Prof. Jang Woo-Yang Ph. D. Dept. of Advanced Parts & Materials Engineering Graduate School of Chosun University

The effects of mechanical properties, texture and annealing temperature on the recrystallization behavior have been investigated in cold-rolled Mg-7%Li-1%Zn, Mg-9%Li, Mg-9%Li-1%Zn and Mg-11%Li-1%Zn alloys. In addition, the effects of alloying element Zn on the tensile properties. The results obtained are as follows; (1) Mg-7%Li-1%Zn, Mg-9%Li and Mg-9%Li-1%Zn alloys consist of α(HCP) + β(BCC) dual phase and, Mg-11%Li-1%Zn alloy has only β phase. The reduction rate in thickness of those alloys are 75, 80, 80 and 90%, respectively. (2) The α phase shows a basal texture with the basal pole tilted ± 25 ° from the normal direction to TD in Mg-7%Li-1%Zn alloy. The α phase presents a basal texture with the basal pole tilted ± 50 ~ 65 ° from the normal direction to RD in Mg-9%Li and Mg-9%Li-1%Zn alloys. (3) The β phase shows texture of (100)±5°[010] in Mg-7%Li-1%Zn, Mg-9%Li-1%Zn and Mg-11%Li-1%Zn alloys. In Mg-9%Li which does not contain Zn, the β phase presents texture of (111)[011]. (4) By cold-rolling, the change in hardness value is proportioned to the volume fraction of α phase. However, the influence of Zn addition on the hardness value is more effective than volume fraction of α phase after annealing. (5) The yield strength decreases but elongation does not show great difference with annealing temperature. The yield strength and elongation increase as Zn is added. This might be caused by the formation of (Mg, Li and Zn) intermetallic compounds and/or solid solution strengthening due to Zn addition. (6) The increasing volume fraction of α phase or alloying the 3rd elements are key factor which increases mechanical properties i.e., yield strength and elongation in of Mg-Li based alloys. However, considering cold workability as press forming materials, the addition of alloying elements is advantageous rather than do that the volume fraction of brittle α phase becomes small.