Effect of Vibration Timing on the Microstructure and Microtexture Formation of AZ91D Magnesium Alloys during Electromagnetic Vibration

Abstract

For an electric conductor in a static magnet, electromagnetic vibration (EMV) is activated to take place when an alternating current flows through the conductor in the direction perpendicular to that of the magnetic field. Following the principle, in the present study we solidified the AZ91D magnesium alloys at various vibration timing moments and then examined the microtexture and microtexture. It is revealed that the decrease of the starting vibration temperature in the mushy zone results in coarse microstructures with large dendritic fragments and eventually with fully developed dendrites that are well oriented with their basal planes being perpendicular to the direction of magnetic field. It has been demonstrated that melt flow is responsible for structural refinement during EMV processing due to the electrical resistivity difference of the solid and liquid. In mushy zone, when vibration is imposed at a low temperature, the fraction solid of the primary phase prior to vibration has been large, which makes the semisolid slurry rather viscous. The intensity and scale of the melt flow is weakened and thus yielding coarse structures. Meanwhile, as the magnetic field is imposed throughout the entire experimental operation, the magnetization torque takes into effect to orient dendrites. The bridging of dendrites may have been accomplished at low vibration temperature before EMV is activated. In this case, the magnetization torque becomes predominant to align crystals along their preferential crystallographic orientation and thus resulting in highly oriented textures. [doi:10.2320/matertrans.M2009056]