AZ91D 마그네슘 合金과 bimodal SiC粒子强化 Mg기 復合材料의 流動性 및 機械的 特性에 關한 硏究 = (A) study on fluidity and mechanical properties of AZ91D Mg alloy and bimodal SiCp/AZ91D composites

다국어 초록 (Multilingual Abstract)

Recently, reduce of natural energy resources and environmental pollution problems are issued in global society. These problems amplify a sense of impending crisis for the survival of mankind. Therefore the world makes an effort to restrain environmental pollution by strengthening restrictions. Especially the exhaust fumes of transportation vehicles are indicated as a major greenhouse factor. For that reason lightweight activity of vehicles are fast dispersed by CAFE(Corporate Average Fuel Efficiency) restriction. Thereby lightweight programs of automobile components for expense efficiency elevation of the fossil fuel are proposed and visible results appeared.
Magnesium alloys are the lightest structural metal and therefore are very suitable for application in the transportation industry. For example, Volkswagen 3l-Lupo and the Audi A2 have air-cooled engines and gearboxes which are the main components that are produced using the Mg alloys AS41, AZ81 and make up of roughly 20kg of the vehicle weight. Magnesium alloy components are usually produced by various casting processes. The most applicable methods are high-pressure die-casting and gravity casting, particularly sand and permanent mold casting. Magnesium alloys offer particular advantages for casting processes. Most alloys show high fluidity, which allows the casting of intricate and thin-walled parts. Magnesium has a low specific heat per unit volume compared with other metals, thereby allowing faster cycle times and reduced die wear. They have high gate pressures because of the low density of magnesium, and iron from the dies has very low solubility in magnesium alloys, which is beneficial because it reduces any tendency to sticking.
Besides, composites consisting of SiC particle reinforced Mg are of particular current interest, because of their potential as low weight, high modulus and strength, high wear resistant materials. Another advantage is processing flexibility, since these composites can be processed via a conventional foundry route. In the latest study, main emphasis is to develop a complete production line in the molten state for particle reinforced magnesium. The RCM(Rotation-Cylinder Method) allows the production of the U-shaped laminar melt surface even at high rotation speed. The melt surface shape of the RCM significantly reduces particle agglomerations and gas entrapment so that a sound composite can be produced in conjuction with gravity permanent or investment casting. Gravity casting is also one of the reasonable solutions for the composites that suffer difficulties in machining and forming in the solid state due to the presence of SiC particles and the HCP structure of magnesium.
In this point of view, this study focus on the gravity casing for the economical practical usage of magnesium alloy and particle reinforced magnesium composite. when the gravity casting applied for the shaping process fluidity of the melt operates major factor for sound castings acquisition. Melt and mold preheating temperature are the major factor of fluidity. In this point of view, Casting conditions of commercial AZ91D magnesium alloy are varied. Based on the above results, bimodal SiCp/AZ91D composite is fabricated by RCM. For the tailoring of the composite effect, fracion of the reinfocement is fixed but mixing ratio is varied. Fluidity, microstructure and mechanical properties of the gravity cast AZ91D magnesium alloy and bimodal SiCp/AZ91D composite are investigated with regard to melt temperature and mold preheating temperature. Fluidity was measured by a spiral fluidity mold. The microstructural features were investigated by optical, scanning electron microscopy(SEM) with energy dispersive spectroscopy(EDS). Mechanical properties with hardness, tensile strengthand proof strength, grain shape and size of the as-castings were also evaluated.
Finally, casting parameters for gravity cast AZ91D magnesium alloy and bimodal SiCp/AZ91D composite are optimized.

목차 (Table of Contents)

• 목차
• 목차 = ⅰ
• List of Tables = ⅲ
• List of Figures = ⅳ
• 1. 서론 = 1
• 2. 이론적 배경 = 4
• 2.1 유동성 = 4
• 2.1.1 유동성의 개념 및 필요성 = 4
• 2.1.2 유동성 측정법 = 5
• 2.2 마그네슘 합금 = 7
• 2.2.1 마그네슘 합금 성형기술 7
• 2.2.2 연구현황 = 8
• 2.3 입자강화 마그네슘 복합재료 = 13
• 2.3.1 입자강화 마그네슘 복합재료 제조방법 = 13
• 2.3.1.1 분말야금법 = 13
• 2.3.1.2 가압침투법 = 14
• 2.3.1.3 무가압침투법 = 14
• 2.3.1.4 XD Process = 15
• 2.3.1.5 분무적층 성형법 = 15
• 2.3.1.6 교반주조법 = 15
• 3. 실험방법 = 17
• 3.1 AZ91D 마그네슘 합금의 유동성 및 기계적특성 평가 실험 = 17
• 3.1.1 유동성 및 충전성 측정 = 17
• 3.1.2 미세조직 관찰 및 기계적특성 평가 시험 = 17
• 3.2 Bimodal SiC 입자강화 AZ91D 마그네슘 복합재료의 유동성 및 기계적특성 평가 실험 = 19
• 3.2.1 복합재료의 제조 및 유동성 측정 = 19
• 3.2.2 미세조직 관찰 및 기계적특성 평가 시험 = 24
• 4. 실험결과 및 고찰 = 25
• 4.1 AZ91D 마그네슘 합금의 유동성 및 기계적특성 평가 = 25
• 4.1.1 주조조건에 따른 유동성 평가 = 25
• 4.1.2 주조조건에 따른 충전성 평가 = 34
• 4.1.3 미세조직 관찰 및 기계적특성 평가 결과 고찰 = 38
• 4.2 Bimodal SiC 입자강화 AZ91D 마그네슘 복합재료의 유동성 및 기계적특성 평가 = 42
• 4.2.1 미세조직 관찰 결과 및 유동성 평가 = 42
• 4.2.2 기계적특성 평가 결과 고찰 = 47
• 5. 결론 = 51
• 6. 참고문헌 = 53
• Abstract = 57