Electron irradiation effects on phase stability of the E （Al18Cr2Mg3） phase have been investigated by high- angle annular dark-field scanning transmission electron microscopy and high-resolution transmission electro...Electron irradiation effects on phase stability of the E （Al18Cr2Mg3） phase have been investigated by high- angle annular dark-field scanning transmission electron microscopy and high-resolution transmission electron microscopy （HRTEM）. The in situ HRTEM observations show that the Ala8Cr2Mg3 particles with different thickness undergo amorphization and dissolution under 300 keV electron irradiation at 25 ℃. The results indicate that the intermetallic compound Al18Cr2Mg3 is unstable under electron irradiation, and structural changes mainly depend on the thickness of particles. Amorphization in the thick particles is caused by a combination of chemical disordering and an increase in point defect concentration. Dissolution after amorphization in the thin particles is attributed to the diffusion of point defect towards the Al matrix.展开更多
This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled...This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled at 200℃. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al;Y phases. After rolling process,anisotropic microstructure was observed. a-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.展开更多
The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mecha...The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.展开更多
Thermo-physical properties of Al-Mg alloys in molten state at 1073 K have been studied using thermodynamic modeling. Thermodynamic properties, such as free energy of mixing, heat of mixing, entropy of mixing, activiti...Thermo-physical properties of Al-Mg alloys in molten state at 1073 K have been studied using thermodynamic modeling. Thermodynamic properties, such as free energy of mixing, heat of mixing, entropy of mixing, activities and structural properties, such as concentration fluctuation in long wavelength limit, Warren-Cowely short range order parameter have been studied at 1073 K, 1173 K, 1273 K and 1373 K on the basis of regular associated solution model. The surface properties such as surface concentrations and surface tension of the liquid alloys have been studied by using Butler’s model. A consistent set of model parameters have also been obtained by using optimization procedure based on statistical thermodynamics. Our analysis reveals that Al-Mg alloy is moderately interacting and it shows ordering nature at 1073 K. The nature of the alloys changes from ordering to segregating as the temperature increases.展开更多
The twinning in the intermetallic compound Al18Cr2Mg3 was observed and identified by transmission electron microscopy.The geometric description of the twinning in Al18Cr2Mg3 with 184 atoms per unit cell was investigat...The twinning in the intermetallic compound Al18Cr2Mg3 was observed and identified by transmission electron microscopy.The geometric description of the twinning in Al18Cr2Mg3 with 184 atoms per unit cell was investigated at atomic level.The classical theory of deformation twinning states that the net atomic displacements are divided into shear and shuffles during twinning.Based on the theory and the hypothesis of full mirror reflection symmetry,the displacement and angle of shuffle were calculated for each atom.The geometric calculation results show that all of the atoms in single crystal Al18Cr2Mg3 have to shuffle.Moreover,the calculation results can be divided into 22 groups,which do not show obvious regularity.展开更多
基金The Project was Supported by Nature Science Foundation of Minstry of Education of Shaanxi Province(09JK718)Scientific Research Foundation of Xi'an Institute of Post and Telecom(ZL2009-32)
基金financially supported by the 111 Project (No. B08040) of ChinaNational Natural Science Foundation of China (No. 51071125)
文摘Electron irradiation effects on phase stability of the E （Al18Cr2Mg3） phase have been investigated by high- angle annular dark-field scanning transmission electron microscopy and high-resolution transmission electron microscopy （HRTEM）. The in situ HRTEM observations show that the Ala8Cr2Mg3 particles with different thickness undergo amorphization and dissolution under 300 keV electron irradiation at 25 ℃. The results indicate that the intermetallic compound Al18Cr2Mg3 is unstable under electron irradiation, and structural changes mainly depend on the thickness of particles. Amorphization in the thick particles is caused by a combination of chemical disordering and an increase in point defect concentration. Dissolution after amorphization in the thin particles is attributed to the diffusion of point defect towards the Al matrix.
基金supported by the National Key Research and Development Program of China(No.2016YFB0301004)the National Natural Science Foundation of China(No.51771115)+1 种基金the Science and Technology Innovation Project(No.009-031-001)Research Program of Joint Research Center of Advanced Spaceflight Technologies(Nos.USCAST2015-25 and USCAST2016-18)
文摘This study was conducted to discuss the effect of rolling strain on microstructure and tensile properties of dual-phase Mg-8Li-3Al-2Zn-0.5 Y（wt%） alloy, which was prepared by casting, and then homogenized and rolled at 200℃. The rolling process was conducted with 10% reduction per pass and five different accumulated strains, varying from 10% to 70%. The results indicate that the as-cast and as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys are composed of α-Mg, β-Li, AlLi and Al;Y phases. After rolling process,anisotropic microstructure was observed. a-Mg phase got elongated in both rolling direction and transverse direction with the addition of rolling strain. Consequently, the strength of the alloy in both directions was notably improved whereas the elongation declined, mainly caused by strain hardening and dispersion strengthening. The tensile properties of the as-rolled alloys in the RD, no matter the YS, UTS or the elongation, are higher than those of the TD due to their larger deformation strain and significant anisotropy in the hcp α-Mg phase. In addition, the fracture and strengthening mechanism of the tested alloys were also investigated systematically.
基金financially supported by the National Natural Science Foundation of China(No.51871043)Fundamental Research Funds for the Central Universities of China(No.N180212010)Liaoning Natural Science Foundation of China(No.2019-MS-113)。
文摘The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill(DC)-casting ingot of 7475 aluminum alloy are obtained.Meanwhile,by analyzing the microstructure,the mechanism of the heterogeneous distribution of E(Al_(18)Mg_(3)Cr_(2))dispersoids in this DC ingot is revealed.The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392,respectively,and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy.After homogenization treatment at 470℃ for 24 h,Mg diffuses uniformly,but Cr hardly diffuses.Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously.The heat treatment at 250℃ for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.
文摘Thermo-physical properties of Al-Mg alloys in molten state at 1073 K have been studied using thermodynamic modeling. Thermodynamic properties, such as free energy of mixing, heat of mixing, entropy of mixing, activities and structural properties, such as concentration fluctuation in long wavelength limit, Warren-Cowely short range order parameter have been studied at 1073 K, 1173 K, 1273 K and 1373 K on the basis of regular associated solution model. The surface properties such as surface concentrations and surface tension of the liquid alloys have been studied by using Butler’s model. A consistent set of model parameters have also been obtained by using optimization procedure based on statistical thermodynamics. Our analysis reveals that Al-Mg alloy is moderately interacting and it shows ordering nature at 1073 K. The nature of the alloys changes from ordering to segregating as the temperature increases.
基金financially supported by the 111 Project (No.B08040) of ChinaNational Natural Science Foundation of China (No.51071125)
文摘The twinning in the intermetallic compound Al18Cr2Mg3 was observed and identified by transmission electron microscopy.The geometric description of the twinning in Al18Cr2Mg3 with 184 atoms per unit cell was investigated at atomic level.The classical theory of deformation twinning states that the net atomic displacements are divided into shear and shuffles during twinning.Based on the theory and the hypothesis of full mirror reflection symmetry,the displacement and angle of shuffle were calculated for each atom.The geometric calculation results show that all of the atoms in single crystal Al18Cr2Mg3 have to shuffle.Moreover,the calculation results can be divided into 22 groups,which do not show obvious regularity.
