Selection of promising quaternary candidates from Mg-Mn-(Sc, Gd, Y, Zr) for development of creep-resistant magnesium alloys

Recently developed Mg-Mn-Sc alloys show a considerable increase of creep resistance at elevated temperature. The endeavor to further improve the properties and to reduce cost of high-price Sc metal initiated a search for additional alloying elements. Gd, Y and Zr were considered for this purpose. The aim is to achieve a large quantity of suitable precipitations to improve mechanical properties using a minimum of expensive alloy element addition. The huge amount of possibilities of combining the elements Mg-Mn-(Sc, Gd, Y, Zr) and the time and cost effort of technological experiments require a preselecting of systems and alloy compositions. Thermodynamic phase diagram and phase amount calculations were performed to give hints for selecting promising candidates. A priority list of three quaternary systems is established: Mg-Mn-Gd-Sc, Mg-Mn-Sc-Y and Mg-Mn-Y-Zr, based on the classification of individual alloys. Most promising is MgMn1Gd55c0.8 (wt.%), but the alloys MgMn1Gd55c0.3 and MgMn1Y5Sc0.8 are also promising. The entire quaternary Mg-Mn-Y-Zr system is disqualified because of phase diagram features that are detrimental for the required microstructural engineering. The focused alloy development following this approach avoids a waste of time and effort. (C) 2001 Elsevier Science B.V. All rights reserved.