Microstructure Evolution of a Semisolid Magnesium Alloy Slurry Obtained via an Internal Rapid Cooling Stirring Process (IRCSP)

Grain refinement of magnesium alloys is an effective way to improve their tensile strength and ductility to meet industrial application requirements. Herein, a new rheocasting process, internal rapid cooling stirring process (IRCSP), was used to obtain a fully grain-refined spherical semi-solid slurry. Rapid quenching was used to study the microstructure evolution during IRCSP. The experimental results showed that the solid fraction was mainly determined by nucleation, and grain growth played only a minor role. The particle density was determined by a combination of the fragmentation and coalescence of solid particles. Changes in grain size over time followed a 1/3 power law with a ripening coefficient. In addition, the particle distribution was determined using shear stress flow and cooling rates. The microstructural analysis suggested that a fast cooling rate led to grain refinement, and rapid stirring enhanced the interfacial energy and stability of the solid-liquid interface. As a result, fine globular primary α-Mg particles were obtained during IRCSP.