The Solidification Behavior of Mg-9Al-2Ca Alloy under Furnace Cooling

Abstract

To understand the solidification pathway and microstructure evolution of Mg-9Al-2Ca alloy, the cooling curve of the alloy solidified under furnace cooling was measured and the water-quenched samples were observed. The experimental results show that the matrix phase of α-Mg dendrites is first generated at 596 °C during the solidification process, then the eutectic phases of Al₂Ca and Mg₁₇Al₁₂ are formed at 518 and 447 °C, respectively, and the solidification is terminated at 436 °C. In the process of solidification, the seaweed dendrites of α-Mg get coarser and are gradually transformed into the global dendrites; besides, the secondary dendrite arms spacing (SDAS) of α-Mg as well as the solid fraction are both increased, while the increasing rate of SDAS of α-Mg and the solid fraction in the temperature region of 600–550 °C is faster than that in the temperature region of 550–436 °C. And a power function relationship can be used to illustrate the change of the SDAS and the solid fraction with the temperature of solidification.

Keywords

Mg-9Al-2Ca alloy / solidification / cooling curve / microstructure evolution