Research On Electromagnetic Modified Technology Of High-performance Magnesium Alloy

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...