Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dend...Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dendrite structure by adding mischmetal to 6063 alloys. This critical mischmetal content is about 0.15%. Only when the mischmetal content is above 0.15%, the secondary dendrite arm spacing decreased and eutectic structure fined. The cast grain is obviously refined when the content of mischmetal is lower. Consideration from the cast structure, the suitable mischmetal content in 6063 alloys is 0.20%.展开更多
Nucleation of dendritic primaryα（Al） phase with addition of element Ce and Sr in hypoeutectic Al-7%Si-Mg cast alloy was investigated by using differential scanning calorimetry （DSC） and scanning electron microsco...Nucleation of dendritic primaryα（Al） phase with addition of element Ce and Sr in hypoeutectic Al-7%Si-Mg cast alloy was investigated by using differential scanning calorimetry （DSC） and scanning electron microscopy. DSC results were used to calculate the activation energy and nucleation work of primaryα（Al） phase. The results show that the values of activation energy and nucleation work are decreased and the nucleation frequency is increased with the additions of Ce and Sr to the alloys. Moreover, the grain size of dendriticα（Al） phase is well refined, and the nucleation temperatures of primaryα（Al） dendrites are decreased with the additions of Ce and Sr. The effects of elements Ce and Sr additions on kinetic nucleation of primary α（Al） phases were also discussed in hypoeutectic Al-7%Si-Mg cast alloy.展开更多
The microstructural evolution of 2026 aluminum alloy during homogenization treatment was investigated by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive X-ray spectrometry(EDS),differential ...The microstructural evolution of 2026 aluminum alloy during homogenization treatment was investigated by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive X-ray spectrometry(EDS),differential scanning calorimetry(DSC)and X-ray diffraction(XRD).The results show that severe dendritic segregation exists in the as-cast 2026 alloy and the main secondary phases at grain boundary are S(Al2CuMg)andθ(Al2Cu)phases.Elements Cu,Mg and Mn distribute unevenly from grain boundary to the inside of as-cast alloy.With the increase of homogenization temperature or the prolongation of holding time,the residual phases gradually dissolve into the matrixα(Al)and all the elements become more homogenized.According to the results of microstructural evolution,differential scanning calorimetry and X-ray diffraction,the optimum homogenization parameter is at 490°C for 24 h,which is consistent with the result of homogenization kinetic analysis.展开更多
Two theoretical criteria represented by Katgerman, and Clyne and Davies for prognosticating hot tearing sensitivity were compared. Both unrefined and grain-refined samples of Al2024 alloy were solidified at various co...Two theoretical criteria represented by Katgerman, and Clyne and Davies for prognosticating hot tearing sensitivity were compared. Both unrefined and grain-refined samples of Al2024 alloy were solidified at various cooling rates ranging from 0.4 to 17.5 °C/s. Thermal analysis was used to detect dendrite coherency point and temperature of eutectic reaction. Curves of solid and liquid fractions were plotted based on Newtonian method to determine hot tearing susceptible areas. The experimental results show that the most susceptible zone in which hot tearing can occur in Al2024 is where Al_2CuMg intermetallic compound forms as a eutectic phase at last stage of mushy-state interval. Also, both criteria are in a good agreement with each other at high cooling rates used in direct-chill casting process while Clyne and Davies＇ model is more acceptable to determine hot tearing tendency from low to medium cooling rates.展开更多
The present study focused on the formation and crystallographic orientation of twinned dendrites coexisting with equiaxed grains in unidirectional solidification of Al-32%Zn(mass fraction)alloy.The morphology was inve...The present study focused on the formation and crystallographic orientation of twinned dendrites coexisting with equiaxed grains in unidirectional solidification of Al-32%Zn(mass fraction)alloy.The morphology was investigated by optical metallograph and electron back-scattered diffraction technique.Results showed that the macrostructure of the alloy exhibited a typical feathery and fan-like structure while the microstructures were elongated lamellas,which were separated by coherent and incoherent twin boundaries.Both the primary trunk and all lateral arms of twinned dendrites grew along〈110〉directions,unlike regular〈100〉α(Al)dendrites.The facet growth of crystals at solid/liquid interface was responsible for the origin of twinned dendrites during the weak local convection,and high thermal gradient and medium solidification velocity had significant contribution to the formation of twinned dendrites.The formation mechanism of twinned dendrites which consisted of three multiplication ways of new twin boundaries formation and one way of dendrite evolution in twin plane was shown schematically.展开更多
文摘Effect of mischmetal addition on the cast microstructure of 6063 alloys has been investigated by means of optical microscopy, TEM and anode filming etc. The results show that there is a critical content of fining dendrite structure by adding mischmetal to 6063 alloys. This critical mischmetal content is about 0.15%. Only when the mischmetal content is above 0.15%, the secondary dendrite arm spacing decreased and eutectic structure fined. The cast grain is obviously refined when the content of mischmetal is lower. Consideration from the cast structure, the suitable mischmetal content in 6063 alloys is 0.20%.
基金Project (42-QP-009) support by Research Fund of the State Key Laboratory of Solidification Processing,ChinaProject (B08040) supported by the Program of Introducing Talents of Discipline to Universities ("111"Project),China
文摘Nucleation of dendritic primaryα（Al） phase with addition of element Ce and Sr in hypoeutectic Al-7%Si-Mg cast alloy was investigated by using differential scanning calorimetry （DSC） and scanning electron microscopy. DSC results were used to calculate the activation energy and nucleation work of primaryα（Al） phase. The results show that the values of activation energy and nucleation work are decreased and the nucleation frequency is increased with the additions of Ce and Sr to the alloys. Moreover, the grain size of dendriticα（Al） phase is well refined, and the nucleation temperatures of primaryα（Al） dendrites are decreased with the additions of Ce and Sr. The effects of elements Ce and Sr additions on kinetic nucleation of primary α（Al） phases were also discussed in hypoeutectic Al-7%Si-Mg cast alloy.
基金Project(2016B090931001)supported by Science and Technology Research and Development Program of Guangdong Province,China
文摘The microstructural evolution of 2026 aluminum alloy during homogenization treatment was investigated by optical microscopy(OM),scanning electron microscopy(SEM),energy dispersive X-ray spectrometry(EDS),differential scanning calorimetry(DSC)and X-ray diffraction(XRD).The results show that severe dendritic segregation exists in the as-cast 2026 alloy and the main secondary phases at grain boundary are S(Al2CuMg)andθ(Al2Cu)phases.Elements Cu,Mg and Mn distribute unevenly from grain boundary to the inside of as-cast alloy.With the increase of homogenization temperature or the prolongation of holding time,the residual phases gradually dissolve into the matrixα(Al)and all the elements become more homogenized.According to the results of microstructural evolution,differential scanning calorimetry and X-ray diffraction,the optimum homogenization parameter is at 490°C for 24 h,which is consistent with the result of homogenization kinetic analysis.
文摘Two theoretical criteria represented by Katgerman, and Clyne and Davies for prognosticating hot tearing sensitivity were compared. Both unrefined and grain-refined samples of Al2024 alloy were solidified at various cooling rates ranging from 0.4 to 17.5 °C/s. Thermal analysis was used to detect dendrite coherency point and temperature of eutectic reaction. Curves of solid and liquid fractions were plotted based on Newtonian method to determine hot tearing susceptible areas. The experimental results show that the most susceptible zone in which hot tearing can occur in Al2024 is where Al_2CuMg intermetallic compound forms as a eutectic phase at last stage of mushy-state interval. Also, both criteria are in a good agreement with each other at high cooling rates used in direct-chill casting process while Clyne and Davies＇ model is more acceptable to determine hot tearing tendency from low to medium cooling rates.
基金Project(51674204)supported by the National Natural Science Foundation of ChinaProject(2016GY-219)supported by Shaanxi Provincial Science and Technology Research and Development Program of China
文摘The present study focused on the formation and crystallographic orientation of twinned dendrites coexisting with equiaxed grains in unidirectional solidification of Al-32%Zn(mass fraction)alloy.The morphology was investigated by optical metallograph and electron back-scattered diffraction technique.Results showed that the macrostructure of the alloy exhibited a typical feathery and fan-like structure while the microstructures were elongated lamellas,which were separated by coherent and incoherent twin boundaries.Both the primary trunk and all lateral arms of twinned dendrites grew along〈110〉directions,unlike regular〈100〉α(Al)dendrites.The facet growth of crystals at solid/liquid interface was responsible for the origin of twinned dendrites during the weak local convection,and high thermal gradient and medium solidification velocity had significant contribution to the formation of twinned dendrites.The formation mechanism of twinned dendrites which consisted of three multiplication ways of new twin boundaries formation and one way of dendrite evolution in twin plane was shown schematically.
