Papers by Author: Henry Hu

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Authors: Li Hong Han, Henry Hu, Derek O. Northwood, X. Nie
Abstract: Dissolution of secondary phases during thermal treatment in cast magnesium alloys influences their engineering properties. In this study, a kinetic model based on a Kissinger-type method has been developed for describing dissolution of secondary phases in the high pressure die cast magnesium alloy AM50 during a thermally activated heating process. Also, differential scanning calorimetry (DSC) was effectively used for investigating the dissolution kinetics of secondary phases in the AM50 alloy. By fitting a kinetic model to the DSC results, the activation energy of the dissolution of the secondary phases can be determined. In parallel, the microstructure of the alloy was analyzed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). It was found that the distribution of secondary phases and the concentration of alloying elements both at the grain boundaries and in the grains play an important role in the solid-state transformation kinetics of die cast magnesium alloy AM50.
Authors: Xue Zhi Zhang, Alfred Yu, Henry Hu
Abstract: In this study, the experimental measurement of the pressure distribution in a cylindrical die cavity for squeeze casting of magnesium alloy AM50A was carried out. Piezo-electric quartz pressure transducers were integrated into a die cavity for real-time pressure measurements. The experimental results revealed that local cavity pressures at various locations changed with time in the duration of squeeze casting solidification and cooling. The pressure transfer rate varied considerably within the casting geometry. The distribution of local cavity pressures was inhomogeneous in the cavity.
Authors: Jun Xiang Zhou, Mohsen Masoumi, Henry Hu
Abstract: In this study, the effect of calcium contents on tensile properties of squeeze cast Mg-Al-Ca alloys at room temperature was investigated. The results show that as the calcium content of AMC50X increases from 0 to 4 wt.%, the ultimate tensile strength (UTS) and elongation-to-failure (Ef) decrease dramatically at room temperature. But, the yield strengths (YS) of the alloys improve slightly.
Authors: Li Fang, Yan Da Zou, Xue Zhi Zhang, Henry Hu
Abstract: In this study, the hexachloroethane (C2Cl6) as a refiner was introduced into a cylindrical squeeze casting of magnesium alloy AM60 with a diameter of 100 mm and a thickness of 25 mm. The casting was prepared under an applied pressure of 30 MPa. The results of tensile testing indicate the tensile properties for the C2Cl6-refined specimens were significantly improved over the untreated AM60 samples. Microstructure analyses with optical microscopes reveal the great grain refining capability of C2Cl6 on squeeze cast magnesium alloy AM60, which should be responsible for the enhanced tensile properties of the refined AM60.
Authors: Ming Zhou, Nai Yi Li, Henry Hu
Abstract: High pressure die cast magnesium alloy AM50 is currently used extensively in complex shaped automotive components with various cross-section thicknesses. Understanding of the effect of section thicknesses on mechanical behavior of AM50 is critical for proper design of different applications. In the present study, magnesium alloy AM50 was high pressure die cast into rectangular coupons with section thicknesses of 2, 6 and 10 mm. The prepared coupons were tensile tested at room temperature. Microstructure analysis and porosity measurement were performed on the representative specimens. The results of tensile testing show that the tensile properties including yield strength (YS), ultimate tensile strength (UTS) and elongation(Ef) decreases with an increase in section thicknesses of die cast AM50. Microstructure and porosity analyses indicate that the observed tensile behavior of die cast AM50 is primarily attributed to the level of porosity which resulted from entrapped gases during the high pressure die casting process.
Authors: Yan Da Zou, Henry Hu, Xue Zhi Zhang
Abstract: The demand for weight reduction in automotive industry has generated great interest in research and development of magnesium applications, especially for powertrain components. Recently, the squeeze casting process is increasingly used on magnesium alloys mainly because of their great ability of eliminating the porosity in the castings. In this study, the effect of hexachloroethane (C2Cl6) as a grain refiner added into the squeeze casting AM60 magnesium alloys was investigated. The results of thermal analysis and microstructural analysis indicate the occurrence of heterogeneous nucleation of primary magnesium during solidification. The microstructural analysis suggests that the nucleation behavior of C2Cl6-treated AM60 alloy may be attributed to the increase in nuclei and nucleation rate during the solidification of the magnesium alloy.
Authors: Henry Hu, Qiang Zhang, Xiao Ping Niu
Abstract: The demand for weight reduction in automobiles has generated strong interest in research and development of magnesium applications, especially for powertrain components. Ca-alloyed magnesium alloys have excellent creep properties and can be potentially used for powertrain applications. In order to better understand their solidification behavior, the grain structure evolution of Ca-alloyed magnesium alloys AM60 has been investigated in this study. The results of thermal analysis and microstructure evaluation indicate the occurrence of heterogeneous nucleation of primary magnesium during solidification. The crystal structural analysis suggests that the nucleation behavior of Ca-alloyed AM60 may be attributed to a good crystallographic match of // .
Authors: Xue Zhi Zhang, Kazi Ahmmed, Meng Wang, Henry Hu
Abstract: In this study a number of thermal treatment schemes over a wide range of temperatures between 120˚ to 350˚ C and times (30 120 minutes) have been experimented in an effort to understand the effect of thermal treatment on tensile properties of vacuum die cast modified aluminum alloy A356. The results show that, the morphology of eutectic silicon has a sound effect on the tensile properties of the tested alloy. The content of magnesium-based intermetallic phases, their morphology and distribution throughout the matrix affect the mechanical properties of the aged alloy as well. The reduction in the strengths of the alloy treated at 350°C for two hours should be at least attributed partly to the absence of the magnesium-based intermetallic phase. However the presence of sufficient amount of magnesium intermetallic phase had played important role in strengthening the alloy thermally treated at 200°C for 90 minutes.
Authors: Li Hong Han, Derek O. Northwood, Henry Hu
Abstract: Mg-Al-Ca alloys with 1wt.% and 2 wt.% Ca additions (AC51 and AC52) were cast by the Permanent Mold technique. The microstructures of the as-cast Mg-Al-Ca alloys were observed by SEM with EDS analysis. The secondary phases were mainly precipitated along the grain boundaries and exhibited a continuous network microstructure for the AC52 alloy and a divorced microstructure for the AC51 alloy. EDS microanalysis showed that the solute (Ca) content in the grains of the AC52 alloy is higher than that in the AC51. A three-sided pyramidal (Berkovich) diamond indenter was used to characterize the local nano-creep behavior at room temperature within the α-Mg in grains. The nano-creep results showed that the AC52 alloy has better creep resistance than the AC51 alloy at all loads at room temperature. The creep exponent n, obtained from the indentation creep data, changes from 6.3 to 3.0 for AC51 alloy and from 6.6 to 3.2 for AC52 alloy at a critical stress (132 MPa for the AC51 and 145 MPa for the AC52). The transition in creep behavior at higher stresses is associated with a change in the deformation mechanisms.
Authors: Zhi Zhong Sun, Alfred Yu, Henry Hu, Li Hong Han
Abstract: In this study, a two-dimensional (2-D) mathematical model was developed to simulate forced and natural convection, heat transfer and solidification occurring during the squeeze casting process. The model was based on the control-volume finite difference approach and on the enthalpy method. The computation was performed to understand the effect of applied pressures on the solidification and cooling behavior of a cylindrical squeeze casting of magnesium alloy AM50A which could have extensive usage in automobiles. The model computed the melt flow fields, the temperature distributions, the cooling curves, the shape and position of the phase front, and total solidification time of the casting. The predicted results show that high applied pressures result in high heat transfer across the casting/die interface, and consequently increase solidification and cooling rates.
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