Computational phase equilibria and experimental investigation of magnesium—aluminum—calcium alloys

摘要

Mg—Al—Ca alloys provide excellent creep resistance and castability for elevated temperature applications. Computational thermodynamics calculations and experimental investigation of the Mg—Al—Ca ternary system have validated the earlier development of creep-resistant AX52 (Mg—5A1-2Ca~1) and AX53 (Mg-5Al-3Ca) alloys. The Scheil simulation of alloy solidification has suggested key guidelines of alloy composition design in promoting the thermally stable (Mg,Al)_2Ca phase, while replacing the less stable Mg_(17)Al_(12) in the microstructure. The suppression of the Mg_(17)Al_(12) phase can increase the solidus temperature, reduce the freezing range, and increase the latent heat during solidification, all of which contribute to improved castability in the AX53 and AX52 alloys compared with the AX51 (Mg-5Al—1Ca) alloy. The quantitative phase equilibrium data, microstructure characterization, as well as the thermal physical properties of the Mg—Al-Ca alloy system generated from this study are important basis for further optimization of alloy composition and microstructure for elevated temperature applications.