Thermodynamic Description of the Al-Mg-Y System

摘要

The Al-Mg-Y system was critically assessed by means of the CALPHAD technique. The solution phases of liquid, face-centered cubic (FCC), body-centered cubic (BCC) and hexagonal close-packed (HCP) were modeled with Redlich-Kister equation. The thermodynamic models of compounds Al_(12)Mg_(17), Al_(30)Mg_(23) and Al_3Mg_2 in the Al-Mg system, AlY_2, Al_2Y_3, AlY and Al_3Y in the Al-Y system, as well as Mg_(24)Y_5 in the Mg-Y system were kept consistent with that of the corresponding binary systems. In order to reproduce the ternary solid solubility of previously determined isothermal section at 400°C, an identical formula of (Al,Mg,Y)_2(Al,Mg,Y) was used to model Al_2Y phase in the Al-Y system and Mg_2Y in the Mg-Y system. The ordered part of BCC phase, i.e. the BCC_B2 phase, was treated with a thermodynamic model of (Al,Mg,Y)_(0.5)(Al,Mg,Y)_(0.5)(Va)_3. The ternary phase of Al_4MgY was described as linear compound with sub-lattice model. On the basis of the optimized thermodynamic parameters of Al-Mg, Al-Y and Mg-Y systems in literature, the Al-Mg-Y system was optimized in present work. The currently calculated isothermal sections at 400 and 800°C, as well as the liquidus surface projection agree well with the previous experimental data.