Development of the New High Shear Technology for Continuous Processing of Mg-Alloys for Ingot Casting

Abstract

Melt quality is crucial for both continuous and shape casting of Magnesium alloys. The recently developed melt conditioning technology where intensive shearing is applied to the melt either by twin-screw or rotor/stator type processing, in order to achieve uniform temperature and chemical composition, together with dispersion and distribution of the harmful inclusions such as oxides that already exist in the melt. Melt conditioning by application of intensive melt shearing of Mg-alloys has shown that MgO films/skins that already exist in the melt can be dispersed into individual particles which can act as potent nucleation sites for the α-Mg phase. Due to this enhanced nucleation during solidification, significant grain refinement is achieved in Mg-alloys including Mg-Al alloys without any specific chemical inoculation. Currently, the melt conditioning technology is limited to batch processing only, hence the need to further develop it into a continuous high shear processing technology which can be used in conjunction with various continuous casting processes such as ingot casting. Here, we report on the development of the new continuous type high shear device with grain refined microstructures of ingots cast after continuous shearing. The preservation of the grain refinement in the melt conditioned ingots after re-melting and casting again is also reported and discussed.