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

References

[1] Qiu W, Liu ZQ, Yu RZ, et al. Utilization of VN Particles for Grain Refinement and Mechanical Properties of AZ31 Magnesium Alloy[J]. J. Alloys. Comp., 2019, 781: 1150-1158.

[2] Liu Y, Zhao YQ, Wang L, et al. Microstructure and Mechanical Properties of AZ31 Alloys Processed by Residual Heat Rolling[J]. J. Wuhan Univ. Technol.-Mat. Sci. Ed., 2021, 36(4): 588-594.

[3] Dargusch MS, Pettersen K, Nogita K, et al. The Effect of Aluminium Content on the Mechanical Properties and Microstructure of Die Cast Binary Magnesium-Aluminium Alloys[J]. Mater. Trans., 2006, 47: 977-982.

[4] Luo AA, Powell BR, Sachdev AK. Computational Phase Equilibria and Experimental Investigation of Magnesium-Aluminum-Calcium Alloys[J]. Intermetallics, 2012, 24: 22-29.

[5] Liang SM, Chen RS, Blandin JJ, et al. Thermal Analysis and Solidification Pathways of Mg-Al-Ca System Alloys[J]. Mater. Sci. Eng. A, 2008, 480: 365-372.

[6] Ghoncheh MH, Shabestari SG, Abbasi MH. Effect of Cooling Rate on the Microstructure and Solidification Characteristics of Al2024 Alloy Using Computer-aided Thermal Analysis Technique[J]. J. Therm. Anal. Calorim., 2014, 117: 1253-1261.

[7] Król M. Solid State Phenomena[M], 2018 Switzerland: Trans. Tech. Publications.

[8] Yavari F, Shabestari SG. Effect of Cooling Rate and Al Content on Solidification Characteristics of AZ Magnesium Alloys Using Cooling Curve Thermal Analysis[J]. J. Therm. Anal. Calorim., 2017, 129: 655-662.

[9] Emadi D, Whiting LV, Nafisi S, et al. Applications of Thermal Analysis in Quality Control of Solidification Processes[J]. J. Therm. Anal. Calorim., 2005, 81: 235-242.

[10] Jafari H, Idris MH, Ourdjini A, et al. In situ Melting and Solidification Assessment of AZ91D Granules by Computer-aided Thermal Analysis During Investment Casting Process[J]. Mater. Des., 2013, 50: 181-190.

[11] Mirković D, Schmid-Fetzer R. Solidification Curves for Commercial Mg Alloys Obtained from Heat-transfer Modeled DTA Experiments[J]. Zeitschrift für Metallkunde., 2006, 97: 119-129.

[12] Suzuki A, Saddock ND, Jones JW, et al. Solidification Paths and Eutectic Intermetallic Phases in Mg-Al-Ca Ternary Alloys[J]. Acta. Mater., 2005, 53: 2823-2834.

[13] Li JL, Chen RS, Ma YQ, et al. Computer-aided Cooling Curve Thermal Analysis and Microstructural Characterization of Mg-Gd-Y-Zr System Alloys[J]. Thermochim. Acta., 2014, 590: 232-241.

[14] Farahany S, Bakhsheshi-Rad HR, Idris MH, et al. In-situ Thermal Analysis and Macroscopical Characterization of Mg-xCa and Mg-0.5Ca-xZn Alloy Systems[J]. Thermochim. Acta., 2012, 527: 180-189.

[15] Ninomiya R, Ojiro T, Kubota K. Improved Heat Resistance of Mg-Al Alloys by the Ca Addition[J]. Acta. Metal. Mater., 1995, 43(2): 669-674.