Crystallographic Study On Solidification Structures Of Zinc Alloys Under High Magnetic Field

In this work,Zn-27.6wt.%Sn,Zn-81.2wt.%Sn-5.9wt.%Bi and Zn-1.8wt.%Mg alloys were solidified in non-directional ways without and with high magnetic fields.The crystallographic growth patterns and the magnetic-field-induced orientations and alignments of the primary zinc-rich crystals were experimentally and theoretically studied with EBSD technique.The inhenent growth mechanism of the primary zinc-rich crystals was discussed,and meanwhile the impact mechanism of the magnetic field on the orientations and alignments of the primary zinc-rich crystals were also analyzed.For the Zn-Sn alloy,plate-like cells are formed when the magnetic field is applied,which grows three-dimensionally in the following pattern:a crystal grows out of the {0001} basal plane to form the horizontally extended<0001>primary trunks;the<0001>primary trunks branch vertically and then produc the<10 10>primary trunks;the<1010>primary trunks branch again in the {0001} basal plane and creat the high-order<1010>arms,some of which then grow out of the{0001} basal plane for the next growth cycle.Without the magnetic field,the primary zinc-rich crystals align and orient randomly;with the magnetic field,they tend to align with the long axis parallel to the magnetic field direction,and their<0001>direction tends to orient preferentially in the direction perpendicular to the magnetic field.For the Zn-Sn-Bi alloy,whether without and with a magnetic fiel the primary zinc-rich phase exhibits a large sheet-like shape in three dimensions,but its edge thickness decreases gradually and its large surface corresponds to the{0001} plane.Without the magnetic field,the primary zinc-rich crystals align and orient randomly;with the magnetic field,they tend to align with the long axis parallel to the magnetic field direction,and their<0001>direction tends to orient preferentially in the direction perpendicular to the magnetic field.For the Zn-Mg alloy,the developed dendritic primary zinc-rich phase is composed of<10 10>primary trunks in the {0001} plane and multiple branched high-order<1010>arms from the primary trunks,and<0001>primary trunks in the direction perpendicular to the {0001} plane and branched high-order<1010>arms from the<0001>primary trunks.Without the magnetic field,the primary zinc-rich crystals align and orient randomly;with the magnetic field,they tend to align with the long axis parallel to the magnetic field direction,and their<0001>direction tends to orient preferentially in the direction perpendicular to the magnetic field.Furthermore,the appearance probabilities of the snowflake-like dendrites in the longitudinal sections and the cross-like dendrites in the cross sections are increased with the increase of magnetic field.