Thermodynamic analysis of the formation reaction of second phases in Mg–Zn–Mn–Sn–Nd alloys

Abstract

The thermodynamic characteristics and solidification sequence of Mg-6Zn-1Mn-4Sn-xNd (x = 0.5, 1.0, 1.0, wt-%, ZMT614-xNd) alloys were investigated using CALPHAD, Miedema model, differential scanning calorimetry and transmission electron microscopy (TEM) analysis. The results revealed that the as-cast ZMT614-Nd alloys consisted of α-Mg, Mn, Mg 7 Zn 3 , Mg 2 Sn and MgSnNd phases. Owing to its higher phase transition temperature and lower formation enthalpy, MgSnNd phase formed first during the casting process. The formation of MgSnNd phase consumed all Nd elements, which restrained the formation of other Nd-containing phases. As a result, the solidification sequence of ZMT614-1.5Nd alloy was α-Mg → MgSnNd → Mn → Mg 2 Sn → Mg 7 Zn 3 . TEM analysis suggested that the MgSnNd phase had a low-symmetry crystal structure.

Effect of Boron on the Grain Refinement and Mechanical Properties of as-Cast Mg Alloy AM50

“…The enthalpy of the three possible B containing compounds Al–B, Mg–B, and Mn–B compounds in the AM 50 + xB alloys was calculated and compared. Some semi-empirical models for thermodynamic calculation have been developed to predict the enthalpy of alloys [18,19,20]. From these, the Miedema model [21] was selected due to its high accuracy to calculate the enthalpy of the three metal diborides in this study.…”