【作者】 房灿峰；

【导师】 金俊泽； 张兴国；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2006， 博士

【摘要】 航空航天和汽车工业对轻质合金的需求不断增长，使得新材料和先进加工技术也得到了很大发展。由于镁合金在物理，机械和铸造方面具有优越的性能，例如：比强度和比刚度高，铸造性能优异，密度低，抗震性能好，热和电导率高等等，被认为是轻质结构件的理想材料。然而，镁合金也具有低硬度，有限的强度，高的化学反应能力以及极差的电腐蚀性能等缺点。以材料加工，磁流体动力学以及材料科学与工程为基础的电磁加工技术被认为是一种重要的前沿加工技术，已经被广泛应用于提高合金的性能，例如，利用磁场和感应电流之间的相互作用来对液体金属产生驱动、搅拌、净化、传输和形状控制等作用。 本文分别将软接触电磁连铸，电磁搅拌和强磁场三种技术应用到镁合金制备过程中。其中，实现镁合金的电磁连铸是工作重点。并研究了各种电磁场对镁合金微观组织和性能的影响，得出了以下主要的结论： 自行设计、建立了适合于镁合金的电磁连铸成型系统与保护系统。在对镁合金电磁连铸的实验缺陷分析后，确定出本实验条件下较为合适的工艺参数：电源频率2500Hz，功率10kW；浇注温度710～730℃；液面控制在感应线圈上沿±2mm处；对于Φ80mm镁合金铸锭，稳定拉速（V₂）为1.5mm／s，Φ120mm为V₂=1.08mm／s；冷却水量为0.6～1.0m³／h。并在此参数下得到了质量较好的镁合金铸锭。软接触电磁连铸铸锭具有细小、均匀的显微组织；且原本在金属模铸锭、普通连铸锭中在晶界上大量析出的β相，在电磁连铸锭中析出减少，并呈现弥散分布的形式。这些组织上的改变，会改善镁合金的性能。软接触电磁连铸力学性能有很大提高。Φ80mm铸锭与金属模铸锭比较，常温抗拉强度和延伸率分别提高了约30％和27％；Φ120mm铸锭与普通连铸锭比较，抗拉强度和延伸率亦提高了约33％和42％。断口形貌显示软接触连铸锭具有更多的韧性断裂特征。同时，软接触连铸锭的宏观硬度比照普通连铸锭也有很大提升：边部提高了14％，心部提高了23％。在3.5％NaCl溶液中的动电位极化测试表明，软接触电磁连铸铸锭耐腐蚀性能有很大的提高。软接触电磁连铸镁合金（Φ80mm）的腐蚀电压为-1.41V，腐蚀电压附近的腐蚀电流密度为3.581μA／cm²。相对于模铸锭，腐蚀电压上升，腐蚀电流下降，耐蚀性能提高。另外，腐蚀形貌也验证了这一结果。 设计制造以永磁体为工作介质的电磁搅拌装置，建立了电磁搅拌作用模型。通过分析得出微体积元在永磁体搅拌过程中在径向和切向上均受到周期变化的作用力。该作用力的大小对改变凝固组织有重要的作用。永磁体搅拌细化了AZ61镁合金的组织，提高更多还原

【Abstract】 The ever-increasing demands for lightweight alloys in the aerospace and automobile industries have led to the development of novel materials and advanced processing techniques. Magnesium alloys are qualified as ideal materials for lightweight constructions because they offer numerous merits in physical, mechanical and casting properties: high specific strength and stiffness, excellent castability, low density, high damping capacity, good thermal and electrical conductivity etc. However, there are some negative features including relatively low hardness, limited strength, high chemical reactivity and inferior galvanic corrosion resistance which has been described as "awful". Electromagnetic processing of materials (EPM), based on materials processing, magnetohydrodynamics (MHD) and materials science and technology, is an important processing technique recognized as a cutting edge technology. And it has been frequently applied to improve the properties and performance of alloys, such as making use of interaction between magnetic field and induced current to produce driving, stirring, purifying, transmitting or shape-control etc. effects on liquid metals.In this paper, soft-contact electromagnetic casting (EMC), electromagnetic stirring and high magnetic field have been performed in the processing of magnesium alloy, respectively. The main part of my dissertation is realization of soft-contact EMC of magnesium alloys, In addition, effects of electromagnetic fields on microstructures and properties of magnesium alloys have been studied. The main obtained results are as follows:An electromagnetic continuous casting system and a protection system applied for magnesium alloys were designed and set up in this study. After many fails and experimental analysis, proper technical parameters have been obtained. Such as power-supply system (2500Hz, 10 kW), pouring temperature of 710~730°C, steady casting speed at 1.5 mm/s for Φ80mm billets and 1.08 mm/s for Φ120mm billets, liquid level equal to upper margin of induction coil ±2mm and the flow rate of cooling water from 0.6 to 1.0 m~3/h are usually used. Under the conditions mentioned above, AZ61 magnesium alloy billets (ΦP80mm, Φ120mm) with good quality are obtained. Soft-contact EMC billets have more fine and uniform grain structure compared with the die cast and direct chill casting (DCC) ones. Moreover in the conditions of soft-contact EMC, precipitation of β-phase particles decreases and disperses, changing the old way in which β-phase particles precipitate chiefly surround a-Mg grain. These更多还原