Effect of a high magnetic field on the macro- and microstructures of Zn-Mg alloy during semi-solid isothermal annealing process

•Semisolid annealing is combined with magnetic field to control structure of Zn-Mg.•Dendrites and particles are distributed in upper and lower parts, respectively.•Decreasing temperature and applying magnetic field promote structural homogeneity.•Magnetic field aligns long axes of platelike particles parallel to field direction.•Magnetic field orients c-axis of all particles perpendicular to field direction. Zn-Mg alloy was isothermally annealed in the semi-solid range under a high magnetic field (HMF). Results showed that, regardless of the HMF, the specimens exhibit inhomogeneous structures, i.e., primary Zn-rich dendrites and granular (nearly spherical or platelike in three dimensions) particles are distributed in the upper and lower parts, respectively. Applying the HMF and decreasing the annealing temperature significantly contribute to the structural homogeneity, which are ascribed to the induced magnetic viscosity resistance force and the higher viscosity of the interdendritic liquid, respectively. Moreover, the HMF aligns the primary dendrites and platelike particles with their longer axes parallel to the HMF direction B. In addition, the HMF preferentially orients all the granular particles with their c-axis perpendicular to B, regardless of their sizes and shapes. The regular alignment and preferential orientation are related to the magnetocrystalline anisotropy of the primary Zn-rich crystals.