Thermal analyses on squeeze cast aluminum alloy A380(SC A380) solidified under 90MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter(DSC) was employe...Thermal analyses on squeeze cast aluminum alloy A380(SC A380) solidified under 90MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter(DSC) was employed. During the DSC runs, heating and cooling rates of 1, 3, 10, and 20 °C·min^(-1) were applied to investigate the heating and cooling effects on dissolution of secondary eutectic phases and microstructure evolution. Various reactions corresponding to troughs and peaks of the DSC curves were identified as corresponding to phase transformations taking place during dissolution or precipitation suggested by the principles of thermodynamics and kinetics. The comparison of the identified characteristic temperatures in the measured heating and cooling curves are generally in good agreement with the computed equilibrium temperatures. The microstructure analyses by scanning electron microscopy(SEM) with energy dispersive X-ray spectroscopy(EDS) indicate that the distribution and morphology of secondary phases present in the microstructure of the annealed sample are similar to the as-cast A380, i.e., strip β(Si), buck bone like or dot distributed θ(Al_2Cu), β(Al_5Fe Si) and Al_(15)(FeMn)_3Si_2. Two kinetic methods are employed to calculate the activation energies of the three common troughs and three common peaks in DSC curves of SC A380. The activation energies of the identified reaction θ_(CuAl_2) = α(Al)+β(Si) is 188.7 and 187.1 k J?mol^(-1) when the activation energies of reaction α(Al)+β(Si)→θCu Al_2 is^(-1)22.7 and^(-1)21.8 k J?mol^(-1), by the Kissinger and Starink methods, respectively.展开更多
LT-3 aluminum alloy is a kind of two-side cladding aluminum special used in vacuum brazing. Differential Scanning Calorimeter （DSC） was used to measure the exothermic and endothermic reaction during the brazing proc...LT-3 aluminum alloy is a kind of two-side cladding aluminum special used in vacuum brazing. Differential Scanning Calorimeter （DSC） was used to measure the exothermic and endothermic reaction during the brazing process that the cortex metal and the base metal are melted and re-crystal. The analysis results inidicate that eutectic reaction is the main reaction in the melted cortex metal crystallization process. But the main reaction in the melted base metal crystallization process is the reaction that α-A1 segregated out. According to the experimental details, the critical work of nucleation is 3.82×10-17J, the critical radius of nucleation is 8.69×10-10 m, the volume of critical crystal nucleus is 2.75×10-27 m3 and the per unit cell in critical crystal nucleus is 43.展开更多
Structuralism and generative approach are two representative syntax theories, which study language from different perspectives. They employ different methodologies i.e. Immediate constituent(IC) Analysis and transform...Structuralism and generative approach are two representative syntax theories, which study language from different perspectives. They employ different methodologies i.e. Immediate constituent(IC) Analysis and transformational-generative(TG)approach to make syntactical analysis. In this paper, these two methods will be applied to analyze some sentences for further discussion and comparison. After analysis by examples, we find that both these two methods have their merits and inadequacies. To some extent, TG method can help IC analysis solve some problems. However, TG grammar is by no means complete and perfect.Improvements are needed to reach its ultimate goal of producing a universal grammar for all human languages.展开更多
基金supported by the Natural Sciences and Engineering Research Council of Canada(NSERC)Discovery(No239080-2010)the project of Shandong science and technology development plan(No2014GGX103035),China
文摘Thermal analyses on squeeze cast aluminum alloy A380(SC A380) solidified under 90MPa were carried out to study the microstructure development of the alloy, in which a differential scanning calorimeter(DSC) was employed. During the DSC runs, heating and cooling rates of 1, 3, 10, and 20 °C·min^(-1) were applied to investigate the heating and cooling effects on dissolution of secondary eutectic phases and microstructure evolution. Various reactions corresponding to troughs and peaks of the DSC curves were identified as corresponding to phase transformations taking place during dissolution or precipitation suggested by the principles of thermodynamics and kinetics. The comparison of the identified characteristic temperatures in the measured heating and cooling curves are generally in good agreement with the computed equilibrium temperatures. The microstructure analyses by scanning electron microscopy(SEM) with energy dispersive X-ray spectroscopy(EDS) indicate that the distribution and morphology of secondary phases present in the microstructure of the annealed sample are similar to the as-cast A380, i.e., strip β(Si), buck bone like or dot distributed θ(Al_2Cu), β(Al_5Fe Si) and Al_(15)(FeMn)_3Si_2. Two kinetic methods are employed to calculate the activation energies of the three common troughs and three common peaks in DSC curves of SC A380. The activation energies of the identified reaction θ_(CuAl_2) = α(Al)+β(Si) is 188.7 and 187.1 k J?mol^(-1) when the activation energies of reaction α(Al)+β(Si)→θCu Al_2 is^(-1)22.7 and^(-1)21.8 k J?mol^(-1), by the Kissinger and Starink methods, respectively.
文摘LT-3 aluminum alloy is a kind of two-side cladding aluminum special used in vacuum brazing. Differential Scanning Calorimeter （DSC） was used to measure the exothermic and endothermic reaction during the brazing process that the cortex metal and the base metal are melted and re-crystal. The analysis results inidicate that eutectic reaction is the main reaction in the melted cortex metal crystallization process. But the main reaction in the melted base metal crystallization process is the reaction that α-A1 segregated out. According to the experimental details, the critical work of nucleation is 3.82×10-17J, the critical radius of nucleation is 8.69×10-10 m, the volume of critical crystal nucleus is 2.75×10-27 m3 and the per unit cell in critical crystal nucleus is 43.
文摘Structuralism and generative approach are two representative syntax theories, which study language from different perspectives. They employ different methodologies i.e. Immediate constituent(IC) Analysis and transformational-generative(TG)approach to make syntactical analysis. In this paper, these two methods will be applied to analyze some sentences for further discussion and comparison. After analysis by examples, we find that both these two methods have their merits and inadequacies. To some extent, TG method can help IC analysis solve some problems. However, TG grammar is by no means complete and perfect.Improvements are needed to reach its ultimate goal of producing a universal grammar for all human languages.
