Hot tearing susceptibility(HTS)of Mg-2Zn-(3+0.5 x)Y-x Al(x=0,2 and 3 at%)alloys is predicted by using modified Clyne-Davies’model(CSC^(∗)).The solidification path,solidification characteristic temperatures and dendri...Hot tearing susceptibility(HTS)of Mg-2Zn-(3+0.5 x)Y-x Al(x=0,2 and 3 at%)alloys is predicted by using modified Clyne-Davies’model(CSC^(∗)).The solidification path,solidification characteristic temperatures and dendritic coherency solid fraction have been studied by double-thermocouple thermal analysis.The solidification contraction stress vs.temperature(and time)curves are measured by using a“T”type hot tearing permanent-mold.The results reveal that the CSC^(∗)prediction values are in good agreement with the experimental results.Moreover,Al_(2)Y phase acts as the heterogeneous nucleation core ofα-Mg and significantly influences the grain size.It has been observed that minimum grain size,optimal dendritic coherency and minimum HTS are exhibited by Mg-2Zn-(3+0.5 x)Y-x Al alloy(x=2).Furthermore,when Al content was increased to 3 at%,Al_(2)Y phase exhibited a peritectic reaction and transformed into a mixed structure of Al_(2)Y and Al+Al_(3)Y phases,which increased the HTS of the alloy due to reduced fine-grained Al_(2)Y content.展开更多
Fine grained Mg-7Gd-5Y-1.2Nd-0.5Zr alloy was investigated by dynamic compression tests using a Split Hopkinson Pressure Bar under the strain rates in the range 1000-2000 s^(-1) and the temperature range 293-573 K alon...Fine grained Mg-7Gd-5Y-1.2Nd-0.5Zr alloy was investigated by dynamic compression tests using a Split Hopkinson Pressure Bar under the strain rates in the range 1000-2000 s^(-1) and the temperature range 293-573 K along the normal direction.The microstructure was measured by optical microscopy,electron back-scattering diffraction,transmission electron microscopy and X-ray diffractometry.The results showed that Mg-7Gd-5Y-1.2Nd-0.5Zr alloy had the positive strain rate strengthening effect and thermal softening effect at high temperature.The solid solution of Gd and Y atoms in Mg-7Gd-5Y-1.2Nd-0.5Zr alloy reduced the asymmetry of α-Mg crystals and changed the critical shear stress of various deformation mechanisms.The main deformation mechanisms were prismatic slip and pyramidal(a)slip,{102}tension twinning,and dynamic recrystallization caused by local deformation such as particle-stimulated nucleation.c 2020 Published by Elsevier B.V.on behalf of Chongqing University.展开更多
Whereas hollow composites present some superiorities like abundant micro interfaces,outstanding impedance matching as the responses of electromagnetic wave(EMW),but versatile designs including crystal transformation,h...Whereas hollow composites present some superiorities like abundant micro interfaces,outstanding impedance matching as the responses of electromagnetic wave(EMW),but versatile designs including crystal transformation,heterogeneous structures and magnetic exchange coupling to further contribution are even not designed or stressed together in previous literatures.In this article,rational design on the hollow CoFe_(2)O_(4)/CoFe@C architecture has been conducted by a sequential process of self-sacrifice by combustion,in-suit polymerization and calcination.Results of morphology observation exhibit that heterogeneous CoFe_(2)O_(4)/CoFe@C composites were generated via crystal transformation from CoFe_(2)O_(4) to CoFe alloys with encapsulated carbon,together with ultimate growth of crystal particles.As for three carbon-based architectures,relatively low-graphitization carbon layers are favorable for enhancing impedance matching and polarization relaxation,but suppressing the conductive loss essentially.Moderate carbon content endows sample S2 with the maximum magnetic saturation(Ms)of 152.4 emu g^(-1).The optimized RL of sample S3 is up to-51 dB with 30 wt%loading,and the effective absorption band(EAB)is of 5.9 GHz at the thickness of 2.17 mm,while 6.0 GHz can be reached at 2.5 mm.Therefore,this hollow multi-interfaces design definitely shed light on novel structure for new excellent absorbers.展开更多
基金The authors would like to acknowledge the financial support from the National Natural Science Foundation of China(Nos.51571145 and 51504153)Innovation Talent Pro-gram in Sciences and Technologies for Young and Middle-aged Scientists of Shenyang(No.RC180111)+2 种基金Doctoral Scientific Research Foundation of Liaoning Province(No.20170520033)Youth Project of Liaoning Education Depart-ment(No.LQGD20170328)Natural Science Foundation of Liaoning Province(No.201602548).In addition,the authors would also like to thank Zhenglai Zhang from Zhejiang Hua Shuo Technology Co.,Ltd.and Ningbo City“Science and Technology Innovation 2025”major special project(new en-ergy vehicle lightweight magnesium alloy material precision forming technology research)funding support.
文摘Hot tearing susceptibility(HTS)of Mg-2Zn-(3+0.5 x)Y-x Al(x=0,2 and 3 at%)alloys is predicted by using modified Clyne-Davies’model(CSC^(∗)).The solidification path,solidification characteristic temperatures and dendritic coherency solid fraction have been studied by double-thermocouple thermal analysis.The solidification contraction stress vs.temperature(and time)curves are measured by using a“T”type hot tearing permanent-mold.The results reveal that the CSC^(∗)prediction values are in good agreement with the experimental results.Moreover,Al_(2)Y phase acts as the heterogeneous nucleation core ofα-Mg and significantly influences the grain size.It has been observed that minimum grain size,optimal dendritic coherency and minimum HTS are exhibited by Mg-2Zn-(3+0.5 x)Y-x Al alloy(x=2).Furthermore,when Al content was increased to 3 at%,Al_(2)Y phase exhibited a peritectic reaction and transformed into a mixed structure of Al_(2)Y and Al+Al_(3)Y phases,which increased the HTS of the alloy due to reduced fine-grained Al_(2)Y content.
基金National Natural Science Foundation of China(Nos.51571145,51404137)City of Ningbo"science and technology innovation 2025"major special project(new energy vehicle lightweight magnesium alloy material precision forming technology)(No.2018B10045).
文摘Fine grained Mg-7Gd-5Y-1.2Nd-0.5Zr alloy was investigated by dynamic compression tests using a Split Hopkinson Pressure Bar under the strain rates in the range 1000-2000 s^(-1) and the temperature range 293-573 K along the normal direction.The microstructure was measured by optical microscopy,electron back-scattering diffraction,transmission electron microscopy and X-ray diffractometry.The results showed that Mg-7Gd-5Y-1.2Nd-0.5Zr alloy had the positive strain rate strengthening effect and thermal softening effect at high temperature.The solid solution of Gd and Y atoms in Mg-7Gd-5Y-1.2Nd-0.5Zr alloy reduced the asymmetry of α-Mg crystals and changed the critical shear stress of various deformation mechanisms.The main deformation mechanisms were prismatic slip and pyramidal(a)slip,{102}tension twinning,and dynamic recrystallization caused by local deformation such as particle-stimulated nucleation.c 2020 Published by Elsevier B.V.on behalf of Chongqing University.
基金This work was supported by the National Natural Science Foundation of China(No.51622106)the Liao Ning Revitalization Talents Program(No.XLYC1807076)。
文摘Whereas hollow composites present some superiorities like abundant micro interfaces,outstanding impedance matching as the responses of electromagnetic wave(EMW),but versatile designs including crystal transformation,heterogeneous structures and magnetic exchange coupling to further contribution are even not designed or stressed together in previous literatures.In this article,rational design on the hollow CoFe_(2)O_(4)/CoFe@C architecture has been conducted by a sequential process of self-sacrifice by combustion,in-suit polymerization and calcination.Results of morphology observation exhibit that heterogeneous CoFe_(2)O_(4)/CoFe@C composites were generated via crystal transformation from CoFe_(2)O_(4) to CoFe alloys with encapsulated carbon,together with ultimate growth of crystal particles.As for three carbon-based architectures,relatively low-graphitization carbon layers are favorable for enhancing impedance matching and polarization relaxation,but suppressing the conductive loss essentially.Moderate carbon content endows sample S2 with the maximum magnetic saturation(Ms)of 152.4 emu g^(-1).The optimized RL of sample S3 is up to-51 dB with 30 wt%loading,and the effective absorption band(EAB)is of 5.9 GHz at the thickness of 2.17 mm,while 6.0 GHz can be reached at 2.5 mm.Therefore,this hollow multi-interfaces design definitely shed light on novel structure for new excellent absorbers.
