The solidification behavior of the AZ61 magnesium alloy during electromagnetic vibration processing

In the present study, we solidified the magnesium-based AZ61 alloy using an electromagnetic vibration technique and investigated the microstructure development as a function of vibration frequency. The microstructure evolution was quantitatively examined in terms of the total average grain size and the individual grain size distribution. The texture was profiled under two different vibration conditions. With respect to the microstructure formation, one can find that a significant difference arises in electrical resistivity between a primary solid and its surrounding liquid in the mushy zone of the alloy, making the solid move faster than the liquid and thus generating uncoupled motion, from which melt flow may be initiated. The influence of this kind non-synchronous motion on microstructure formation is discussed as a function of vibration frequency when considering the intensity of melt flow during EMV processing. For the Mg-based alloy with a hexagonal closed-packed crystal lattice, it is subject to magnetization torque due to the anisotropic magnetic susceptibility along c-axis and a,b-axes. The Lorentz force induces melt flow that stirs the semisolid slurry to form random textures while the magnetization torque suppresses melt flow that rotates crystals to align along their easy magnetization direction. The resultant structure and texture can be well elucidated when considering the competition of two kinds of force under two different vibration conditions by terminating the vibration at different temperatures during processing.