Formation of non-dendritic microstructures in preparation of semi-solid Mg-RE alloys slurries: Roles of RE content and cooling rate

摘要

The proper alloy composition ranges for rheo-forming of Mg-RE alloy was obtained through thermodynamic calculations. The low frequency electromagnetic stirring (LFEMS) process was used to fabricate semisolid slurries of Mg-Gd-Zn series alloys, and the role of solute Gd content and the cooling rate in the LFEMS process were systematically investigated. Both the Gd content and cooling rate show effective influences on the microstructure of the Mg-Gd-Zn alloy semisolid slurries. Fine and spherical primary Mg phase can only be obtained by decreasing the cooling rate to less than 1.4 C degrees/min and increasing the solute Gd content to no less than 9 wt. %. The formation mechanism of non-dendritic morphology of primary Mg phase in Mg-Gd-Zn alloy was proposed to be the dendrite arm root re-melting induced by curvature undercooling and ripening induced by low cooling rate.