Preparation of Mg–Nd–Zn–(Zr) alloys semisolid slurry by electromagnetic stirring

The effects of electromagnetic stirring (EMS) including stirring time, applied voltage and rotational frequency on the microstructure of semisolid slurries of the Mg–Nd–Zn–(Zr) alloys were investigated. The results indicate that all of the parameters have large effects on the microstructure of the slurries. After being treated by EMS, the morphology of primary α-Mg phases in the Mg–3Nd–0.2Zn (NZ30) alloy slurries evolves from dendrite to three types: rosette, dendrite, and spheroid, while a semisolid microstructure with small and spheroidal particles is obtained in the Mg–3Nd–0.2Zn–0.4Zr (NZ30K) alloy slurries. The data for solid fraction with stirring time can be fitted to linear equations. The increase of applied voltage and rotational frequency makes the primary α-Mg phases initially refined and then coarsened. The optimal processing parameters are stirring time 120–180s, applied voltage 300–350V, rotational frequency ~20Hz for NZ30 alloy, and stirring time 30–180s, applied voltage ~350V, rotational frequency ~20Hz for NZ30K alloy. The average particle size of NZ30 alloy can be refined from ~879 to ~457μm. Furthermore, the effects of applied voltage and rotational frequency on undercooling and melt temperature were also discussed on the basis of thermodynamic theory. [Display omitted] •Mg–3Nd–0.2Zn (NZ30) and Mg–3Nd–0.2Zn–0.4Zr (NZ30K) alloy semisolid slurries were prepared by electromagnetic stirring.•Increase of voltage or decrease of frequency led to the increase of undercooling and melt temperature.•The optimal parameters for Mg–3Nd–0.2Zn and Mg–3Nd–0.2Zn–0.4Zr alloy slurries were obtained.•Three types of primary α-Mg particles were obtained in NZ30 alloy semisolid slurry: rosette, dendrite, and spheroid.