Thermochemical modelling of Magnesium alloys

I have recently been asked what FactSage can offer a potential customer working with cast Magnesium alloys. The short answer is: A lot! The long answer I want to share here:

The largest thermochemical database available for light metals, FTlite, is integrated in FactSage. FTlite is developed by researchers at CRCT, Polytechnique Montreal, and McGill University, Montreal. Today, FTlite contains excellent thermochemical descriptions of both Aluminium and Magnesium alloys. For Magnesium alloys, the following 45 (!) alloying elements can be considered: Ag, Al, B, Ba, Be, Bi, C, Ca, Ce, Cr, Cu, Dy, Er, Eu, Fe, Gd, Ge, H, Ho, In, K, La, Li, Lu, Mg, Mn, Na, Nd, Ni, Pb, Pr, Sb, Sc, Si, Sm, Sn, Sr, Tb, Ti, Tm, V, Y, Yb, Zn, Zr. Therefore, all major commercial Magnesium alloys can be calculated using FactSage.

Fig. 1: Optimized systems in FTlite (Reference)

Now the question is: What can FactSage do, if you have FTlite? Let us start from the liquid Magnesium melt. First of all, you will be able to calculate solubilities of additives in the liquid melt and liquidus temperatures. When you reach temperatures below the liquidus, you will be able to calculate the solidification pathway, either considering equilibrium cooling or Scheil cooling. Take the example alloy Mg-Zn4REZr (or: ZE41, RZ5). The standards do not specify which Rare Earth element (RE) is used. Therefore, the manufacturer has a lot of freedom in the choice of individual alloy composition. In the following diagrams, Scheil cooling is shown for two different alloy systems, one with Ce and Nd as REs and other with Gd and Y.

More drastic differences are observed when you model the heat treatment of the cast alloy: After annealing at 330°C, the alloy containing Ce and Nd show a RE content in the matrix of 0.01 wt.% which is 0.1 wt.% for the alloy containing Gd and Y.  At T5 condition (after annealing at 180°C), the first alloy shows predominantly precipitation of the Tau4 phase with a fraction of this strengthening phase of 0.04% while the Gd and Y containing alloy precepitates predominantly the I-phase with fraction of 3.6%. Therefore, stronger strengthening can be expected for this alloy.

Do you have a question concerning thermochemical modelling of Magnesium alloys? Do not hesitate to contact me or leave a comment below the article!

Further information:

FTlite Database description.

In-Ho Jung, Zhijun Zhu, Junghwan Kim, Jian Wang, Patrice Chartrand, Arthur Pelton, Recent Progress on the Factsage Thermodynamic Database for New Mg Alloy Development, JOM, Vol. 69, No. 6, 1052, 2017.

G. Eriksson, M. to Baben, K. Hack, FactSage Developments: Scheil phase formation diagrams, Presentation at the 2016 GTT User’s Meeting.

FactSage Alloy Design Application Examples.

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