Experimental Investigation and Thermodynamic Calculation of Mg-Al-Sn Phase Equilibria and Solidification Microstructures

Abstract

Experimental work using differential scanning calorimetry, differential thermal analysis, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis was conducted on key samples with more than 33 at.% Mg in the Mg-Al-Sn system. In addition to the thermal analysis and study of the solidification microstructure, an equilibration at 400°C was performed. The results were used together with all available phase equilibria and thermodynamic data from earlier experimentation to create a consistent thermodynamic description of the MgAl-Sn alloy system. No ternary stable phase was discovered, and no ternary solubilities of the binary intermetallic phases were found. With the addition of a single Gibbs energy parameter describing the interaction between Al and the associate Mg 2 Sn in the liquid phase, the thermodynamic model of the system could be made to describe all pertinent experimental data throughout the ternary system. The phase precipitation sequence during slow solidification of all present samples is reflected by the thermodynamic calculations as well. Intricate details of the liquid miscibility gap, occurring in ternary alloys only, are also highlighted.

Solidification Microstructure and Mechanical Properties of Cast Magnesium-Aluminum-Tin Alloys

“…No stable ternary phase was discovered, and no ternary solubility of the binary intermetallic phases was found in this calculation, which is consistent with a previous study. [10] Two binary phases, Mg 2 Sn and Mg 17 Al 12 , are important to this alloy system; the Mg 2 Sn phase is reported to provide significant strengthening, [3] whereas the Mg 17 Al 12 phase improves strength, [12] corrosion, and castability, [13] but reduces ductility and creep resistance. [2] In designing new Mg-Al-Sn alloys for automotive structural applications, mechanical properties and corrosion resistance are primary considerations.…”

“…Although the binary phase diagrams of Mg-Sn, Al-Sn, and Mg-Al systems are well established, [7][8][9] the thermodynamic data of the Mg-Al-Sn system was made available only recently. [10] Therefore, thermodynamic calculations of the Mg-Al-Sn system were carried out using a software package Pandat developed by CompuTherm (Madison, WI). [11] The calculated phase diagrams, phase constituents, and solidification paths were then used to design the alloy composition with balanced mechanical properties.…”

Evaluation of Calphad Approach and Empirical Rules on the Phase Stability of Multi-principal Element Alloys

“…This is a result of the thermodynamic modeling of liquid phase and has not been justified by experimental work. But one can not excluded the existence of the miscibility gap in the liquid phase either, with considering the existence of miscibility gap in Mg-Al-Sn ternary system [53] and the experimentally detected existence of short-range ordering in Li-Sn binary system. [54,55] Although the reliability of the database for Al-Li-Mg-Sn-Zn quinary system has not been verified by any five-component system, all the binary sub-systems have been thermodynamically assessed and properly modeled.…”

Refined microstructure and improved mechanical properties of high-ratio extruded AZ91−xSn magnesium alloy

“…MgeAleSn phase diagram [26], the solid solubility of Sn in Mg at room temperature is nearly zero, so the Mg 2 Sn phase precipitated even when the Sn content was only a few percent. The theoretical fractions of constituent phases, based on the lever rule and listed in Table 1 were dispersed at the grain boundaries of the eutectic b-Mg 17 Al 12 [27].…”