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.

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

“…Our previous experimental results [16] revealed that EMV can take into effect to modify solidification structures when vibration is operated in mushy zone in which the primary solid and the remaining liquid coexist. In this hybrid region at high temperature, it has been well known that the electrical resistivity of a solid is much smaller than that of its counterpart liquid with similar composition.…”

Refinement of Microstructure of JIS A7204 and A6022 Aluminum Alloys Solidified by Electromagnetic Vibration Technique

“…The imposition of EMV above liquidus only, i.e., prior to the formation of a primary solid phase, or far below the liquidus with a great amount of fraction solid cannot produce refinement, as we have demonstrated in AZ91D magnesium alloys. 34) This is why the imposition in the present study commenced from 700°C and then through the semisolid region. This operation could guarantee that the present EMV was imposed effectively in refining solidification structures.…”

Segmentation and Alignment of Nd2Fe14B Platelets in Nd-Cu Eutectic Alloys Using the Electromagnetic Vibration Technique

“…It is noted that in the magnesium-based [50] and 7xxx aluminum alloys, [51] the weight fraction of the primary solid solution phase increases continuously from naught to unit once the alloys are cooled from liquidus to solidus. [24,41,42,52] Therefore, the primary solid phase crystallized just below the liquidus immerses and floats freely within the liquid pool. However, in the present alloys, the weight fraction of the Nd 2 Fe 14 B phase remains as high as 30 and 50 pct when the alloys are cooled from 700°C up to the eutectic temperature.…”