Mg합금의 고온변형과 기계적 성질 및 감쇠능에 관한 연구

Abstract

Magnesium is known to have a good damping capacity compared to other known metals and their alloys. Also, the damping properties of metals are generally recognized to be dependent on microstructural factors such as grain size and dislocation etc. However, there are only few studies about the damping capacity of magnesium alloys. Therefore, in this study, effect of heat treatment on the microstructure, their mechanical properties and damping capacity of two kinds of specimens AZ31 (Mg-3Al-1Zn in mass%) and AZ61(Mg-6Al-1Zn in mass%) magnesium alloys ware investigated. The results obtained from the experiment are summarized as follows, As a result of microstructure observation after hot-rolling, dendrite structure was formation and compounds was precipitated along the grain boundary in two kinds of specimens, and this precipitated compounds is found to be Mg17Al12. The Mg17Al12 compounds and dendrite ware decomposed and dissipated by annealing treatment. With increasing the annealing temperature and time, damping capacity was slowly increased by the growth of grain size and decreasing of defects. Also, two kinds of magnesium alloys after annealing show no difference in damping capacity. After annealing of hot-rolled magnesium alloys, damping capacity rapidly decreased with an increase of strength. Strength and damping capacity show proportional relationship. From the microstructure observation, fine and coarse grains were existed together by occurrence of DRX (Dynamic recrystallization) during high-temperature. The lower strain rate and higher temperature lead grain size to increases. At the beginning stage, after the maximum stress (work softening) appeared, true stress decrease with an increase of true strain in all specimens. The faster strain rate and lower temperature, work softening behaviors rapidly occur. In case of flow stress, faster strain rate and lower temperature, flow stress increases. However, there were no differences according to the direction of processing. The lower strain rate and higher temperature, strain rate sensitivity index decreases. The degree of spring back is higher with increasing the radious of curvature, and the higher temperature and lower strain rate, spring back slightly increases. After hot working, the strength of AZ61 magnesium alloy is much higher than that of AZ31 magnesium alloy. However, the elongation of two kinds of magnesium alloy do not show a significant difference. In case of damping capacity, with an increase of strength and elongation, damping capacity rapidly decreases.