전자기장을 이용한 AZ31 마그네슘 합금 빌렛 주조에 대한 엔지니어링 연구

Abstract

With the adoption of the Paris Climate Treaty, the importance of environmental and energy issues has once again highlighted globally. Major industrial fields such as automobiles, aerospace, steelmaking, and electrical appliances have been intensively conducted research to replace steel with environmental-friendly materials that are lightweight, energy efficient and highly recyclable. Magnesium alloy is a typical alternative material for steel because it has abundant reserves, excellent specific strength and high recycling rate. However, Magnesium alloy is low in heat capacity and contain many solute elements, so it is weak to micro segregation and crack defects during casting process. In this thesis, electromagnetic stirrer (EMS) is proposed to resolve these casting problems. EMS generates a rotating flow in a mold to reduce air bubble, micro segregation and crack defects. The shear force due to the rotational flow increases the number of nucleus growth by cutting the dendrite and minimizes the temperature deviation, thereby ensuring excellent casting quality. In order to optimize EMS, the solidification characteristics of magnesium alloy billets were analyzed by numerical analysis method. First, the optimal mold cooling condition without break-out was confirmed. Secondly, the change of solidification profile and pool depth according to continuous casting speed were analyzed. Third, the change of the rotating flow in the mold according to the conditions of the electromagnetic field was observed and the optimum current and frequency were suggested. As the casting speed increased, the temperature deviation on the meniscus decreased and the pool depth deepened. The smaller the current in the electromagnetic field, the less the temperature deviation, because the rotating flow below submerged entry nozzle (SEN) interfere the flow to rise. Conversely, the higher the frequency of the electromagnetic field, the less the temperature deviation and the lower the pool depth.