Technical Study On Soft-contact Electromagnetic Casting Of Magnesium Alloys

Magnesium alloys have better properties, such as high strength-weight ratio, high damping capacity, stable physical dimension, excellent electromagnetic shielding capability and good machinability etc. Furthermore, Magnesium alloys also provide high efficiency of recycling. As the lightest metal in practice, magnesium and its alloys become attractive material both in domestic and abroad.Electromagnetic continuous casting is a new material processing method, which combined magneto-hydrodynamics (MHD) with metallurgical engineering. The outstanding merits of EMC lie in producing billets or ingots with smooth surface, good mechanical properties and bringing high production efficiency. EMC has become an important method to carry out continuous casting & rolling and produce high quality components. Magnesium alloys can be produced by nearly all the metal fabrication methods, such as casting, bulking working and mechanical forming etc. Magnesium wrought alloys and their casting technologies develop slowly and need to be innovated in practice. Except proper chemical composition, obtaining good casting materials with less inclusion, fine grain and dense structure is the key to develop the super-fine and high strength Mg alloys.This paper describes the casting process and technical parameters of soft-contact EMC for magnesium AZ61 billets. Microstructure and mechanical properties of the EMC billets are compared with the billets cast by the direct chill method.The liquid alloy is made by meling pure Mg, Al and Zn. By using the soft-contact EMC technology, the billet structure are refined and the segregation are reduced. At the same time the inclusion distribution is improved. Magnesium wrought alloy with excellent quality is obtained in the experiment.AZ61 magnesium alloy billets(F 120mm) with good surface quality are obtained at the following casting condition: casting temperature 720℃ ~740℃,flow rate of cooling water 0.8t/h~1.0t/h, casting speed 1.0mm/s, power supply frequency 2500Hz, power 8~10Kw. Protection gas (air, CO2, SF6) can reduce surface oxidation significantly. Mechanical properties of both EMC and DC casting billets are compared.The experiment shows that the soft-contact EMC can change the initial solidification process, i.e., reduce the contact area and pressure between the liquid metal and the mold wall,result in the improved surface quality. Liquid metal solidifies under the common effects of the electromagnetic force and cooling water. Electromagnetic stirring homogenizes the microstructure and refines the coarse grain zones in the billet. Mechanical properties are greatly improved, e.g., hardness, strength and elongation have been increased by 20%, 10-25% and 55% respectively.