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Study on Phase Equilibrium of Mg-Zn-Ca Ternary System in Mg-Rich Corner
Author: MaZuoZuo
Tutor: LiHongXiao
School: Northeastern University
Course: Materials Science
Keywords: Mg-Zn-Ca ternary compound phase diagram isothermal section
CLC: TG146.22
Type: Master's thesis
Year: 2010
Downloads: 77
Quote: 0
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Abstract
Property advantages of magnesium-based alloys failed to be used fully because of the poor heat resistance. Alloying is an effective way to improve it. Zn and Ca additions is expected to improve creep resistance of magnesium-based alloys. But study on the phase equilibrium of Mg-Zn-Ca Ternary System, in particular the study on the composition range of ternary compound, crystal structure and thermal stability, there are still big difference.In this thesis, structure analysis on alloy equilibrium microstructure is used to study the phase equilibrium of Mg-Zn-Ca Ternary System in Mg-rich corner, by optical and scanning electron microscopy microstructure analysis, the spectrum composition analysis and X-ray diffraction with the aid of differential thermal analysis. The following valuable results obtained can provide basis on component design and organizational control of heat-resistant magnesium alloys.The results of the study show that in the Mg-rich corner of Mg-Zn-Ca Ternary System exist ternary compound T1and T2which can equilibrium with magnesium-based solid solution. Component range of T1:35.5-68.0at%Mg、16.7-50.0at%Zn and13.9-16.2at%Ca, it’s hexagonal structure, lattice constant a is decreasing with Zn content increasing. Component range of T2:25.9-28.4at%Mg、63.0-66.3at%Zn and7.2-8.6at%Ca, it’s also hexagonal structure. The existence temperature of T1and T2is higher than400℃.At300℃, in the Mg-rich corner of Mg-Zn-Ca Ternary System exist three-phase regions:(Mg)+Mg2Ca(Zn)+T1、(Mg)+T1+T2、(Mg)+MgZn(Ca)+T2and MgZn(Ca)+Mg2Zn3(Ca)+T2.At400℃, in the Mg-rich corner of Mg-Zn-Ca Ternary System exists a large liquid region, it’s component range:61.5-71.6at%Mg、20.6-33.7at%Zn and0-8.5at%Ca. It also exists four three-phase regions:(Mg)+Mg2Ca(Zn)+T1、(Mg)+T1+Liq、Liq+T1+T2and Liq+T2+Mg2Zn3(Ca).
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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallic materials > Non - ferrous metals and their alloys > Light non-ferrous metals and their alloys > Magnesium
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