In order to develop high strength Mg-Gd-Y-Zn alloys,key experiments coupled with CALPHAD(CALculation of PHAse Diagrams)calculations were carried out in the current work to provide critical understanding of this import...In order to develop high strength Mg-Gd-Y-Zn alloys,key experiments coupled with CALPHAD(CALculation of PHAse Diagrams)calculations were carried out in the current work to provide critical understanding of this important alloy system.Three Mg-10 Gd-xY-yZn(x=4 or 5,y=3 or 5,wt.%) were mapped on Mg-Gd-Y-Zn phase diagrams for phase equilibria and microstructure investigation.Electron microscopy was performed for phase identification and phase fraction determination in as-cast and solution treated conditions.In all three alloys,the major phases were Mg-matrix and long period stacking order(LPSO) 14 H phase.With ST at 400 and 500℃,the phase fraction of LPSO 14 H increased,particularly the fine lamellar morphology in the Mg matrix.The as-cast and 400℃ Mg10 Gd5 Y3 Zn samples had Mg(Gd,Y) present.At 500℃,Mg(Gd,Y) is not stable and transforms into LPSO 14 H.The Mg 10 Gd5 Y5 Zn alloy included the WPhase,which showed a reduction in phase fraction with solution treatment.These experimental results were used to validate and improve the thermodynamic database of the Mg-Gd-Y-Zn system.Thermodynamic calculations using the improved database can well describe the available experimental results and make accurate predictions to guide the development of promising high-strength Mg-Gd-Y-Zn alloys.展开更多
The phase constitution and solidification pathways of AZ91＋xSb（x = 0, 0.1, 0.5, 1, in wt%） alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculat...The phase constitution and solidification pathways of AZ91＋xSb（x = 0, 0.1, 0.5, 1, in wt%） alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91＋xSb（x = 0.1, 0.5, 1） is composed of a-Mg matrix, b-Mg17Al12 phase, and intermetallic compound Mg3Sb2. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg3Sb2 phase forms after a-Mg nucleation, thus impossible acts as heterogeneous nucleus for a-Mg dendrite. Besides,the solid fraction at dendrite coherency point（fDCPs） determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.展开更多
基金partially funded by the Army Research Laboratory (ARL) and Terves LLCsupported by the Army Contracting Command - Adelphi, MD under Contract No W911QX-18-P-0038
文摘In order to develop high strength Mg-Gd-Y-Zn alloys,key experiments coupled with CALPHAD(CALculation of PHAse Diagrams)calculations were carried out in the current work to provide critical understanding of this important alloy system.Three Mg-10 Gd-xY-yZn(x=4 or 5,y=3 or 5,wt.%) were mapped on Mg-Gd-Y-Zn phase diagrams for phase equilibria and microstructure investigation.Electron microscopy was performed for phase identification and phase fraction determination in as-cast and solution treated conditions.In all three alloys,the major phases were Mg-matrix and long period stacking order(LPSO) 14 H phase.With ST at 400 and 500℃,the phase fraction of LPSO 14 H increased,particularly the fine lamellar morphology in the Mg matrix.The as-cast and 400℃ Mg10 Gd5 Y3 Zn samples had Mg(Gd,Y) present.At 500℃,Mg(Gd,Y) is not stable and transforms into LPSO 14 H.The Mg 10 Gd5 Y5 Zn alloy included the WPhase,which showed a reduction in phase fraction with solution treatment.These experimental results were used to validate and improve the thermodynamic database of the Mg-Gd-Y-Zn system.Thermodynamic calculations using the improved database can well describe the available experimental results and make accurate predictions to guide the development of promising high-strength Mg-Gd-Y-Zn alloys.
基金financially supported by the National Basic Research Program of China (No. 2013CB632202)the National Natural Science Foundation of China (Nos. 51105350 and 51301173)
文摘The phase constitution and solidification pathways of AZ91＋xSb（x = 0, 0.1, 0.5, 1, in wt%） alloys were investigated through ways of microstructure observation, thermal analysis technique, and thermodynamic calculation. It was found that the non-equilibrium solidification microstructure of AZ91＋xSb（x = 0.1, 0.5, 1） is composed of a-Mg matrix, b-Mg17Al12 phase, and intermetallic compound Mg3Sb2. The grain size of the alloys with different Sb contents was quantitatively determined by electron backscattered diffraction technique which shows no grain refinement in Sb-containing AZ91 alloy. Thermodynamic calculations are in reasonable agreement with thermal analysis results, showing that the Mg3Sb2 phase forms after a-Mg nucleation, thus impossible acts as heterogeneous nucleus for a-Mg dendrite. Besides,the solid fraction at dendrite coherency point（fDCPs） determined from thermal analysis decreases slightly with increasing Sb content, which is consistent with the fact that Sb does not refine the grain size of AZ91 alloy.
