Part Of The Mg Alloy Phase Diagram Determination And Thermodynamic Calculations

Magnesium alloys have been drawn considerable attentions both in structural materials and functional ones, for example, the application in automobiles,3C productions as well as energy related hydrogen storage materials. Among them, rare-earth elements are selected as effective and promising alloying elements in the development of castable heat resisitant magnesium alloys due to the formation of high stability intermetallic compounds. In this work, with finance supported by national scientific foundation No.50731002, experimental investigation to phase diagrams and microstructural analysis of relative ternary alloys have been carried out, including Mg-Ni-Gd, Mg-Sr-(Nd,Gd). Mg-Al-Zn-Sm quaternary alloys have been designed and prepared assisted by thermodynamic calculation.1. An isothermal section of the Mg-Ni-Gd ternary system at 673 K was constructed. Six ternary compounds were identified in this work, three of which were observed to crystallize in the Cu4MgSn (Ï„1), Mo2FeB2 (Ï„2) and Ru4Al3B2-type (Ï„3) structures, respectively. A long period stacking ordered (LPSO) phase was identified to have an 18R structure and a melting temperature of 806 K. Noticeable solid solution of Ni in the Mg5Gd and Mg3Gd binary compounds occur.2. Phase equilibria of the Mg-Sr-(Nd,Gd) ternary systems were critically investigated by using equilibrated alloys. From the EPMA, XRD obtained over the Mg-rich composition range. A ternary compound with identical crystal structure of Mg41Ce5 was discovered in Mg-Sr-Gd. Binary compounds in both ternary systems exhibited noticeable homogenerous solubilty such as Mg5Gd Mg3Gd, Mg41Nd5 and Mg3Nd3. Mg-Al-Zn-Sm alloy was designed by CALPHAD technology, including alloy composition and process parameters. According to T6 heat treatments, tensile experiments indicated ultra tensile strength of 263 MPa in alloy sample of the composition Mg-6Al-1.3Sm-1Zn (wt.%). Mg/Zn solid solution matrix, Al2Sm and Mg17Al12 precipitations were determined. The microstrual evolution and the phase transformation point are consistent with the thermodynamic calculation.