Papers by Author: Wei Min Zhao

Abstract: Closed-cell aluminum foam with different percentages of Cu was prepared by melt foaming method.The effect of Cu element on the quasi-static compressive properties of aluminum foam was investigated, both under as-cast and heat-treated conditions. The results showed that Cu element distributed in cell wall matrix mainly in the forms of Al-Cu solid solutions and AlCu3, Al_6.1Cu_1.2Ti_2.7 intermetallics. Meanwhile, Cu-containing foams possessed much higher compressive strength than the commercially pure aluminum foams. Additionally, proper heat treatment could further improve the yield strength of Cu-containing foams and the effect of aging treatment was more obvious than the homogenizing heat treatment under the present conditions and the reasons were discussed.

Abstract: Magnesium alloys are very active and readily ignite during heating and melting. In this study, the ignition-proof property of AZ91D with Nd and Dy addition was discussed, and the effects of these ignition-proof elements on the microstructure and microhardness of AZ91D investigated. The results show that the ignition-proof performance of magnesium alloy is improved obviously. The ignition resistance is attributed to the compact oxide films, which consist of MgO, Al₂O₃, Nd₂O₃, Dy₂O₃. When Dy content increased beyond 0.5%, the change tendency of ignition point of the alloy follows the shape of “v” curve, and the ignition point increased with Nd addition. The optimum composition of the newly developed magnesium alloy is AZ91D-3Nd-0.5Dy with the ignition point about 60K higher than AZ91D. And also AZ91D-3Nd-0.5Dy has fine microstructure and higher microhardness.

Abstract: In order to develop ignition resistant magnesium alloy, Ca and Ce elements were selected alloying elements to fabricate Mg alloy. Different content of Ce (0,0.5,0.8,1.2,1.5wt%) and Ca (0, 0.6,0.8,1.0wt%) were added into pure magnesium to analyze their ignition-proof effect. The concentration of Ce and Ca elements on the melt surface was believed to be key factor for ignition resistance, which caused the change of interfacial tensions. It was indicated that the ignition resistance could be improved with increase of Ce and Ca addition. This could be attributed to a protective surface oxide owing to the diffuse of Ce and Ca to surface.

Abstract: This paper focus on the effect of rare earth elements addition on the oxidation resistance of pure magnesium. The results show that the ignition points of the Mg-RE alloys vary like “V” along with the increase of the rare earth elements. When the content of Y reaches 10wt%, the ignition point of magnesium alloy is 890K, about 40K higher than the ignition point of pure magnesium. After the addition of rare earth elements, dense oxide film forms on the surface of Mg-RE alloys. The outer oxidation film mainly consists of rare earth oxide.

Abstract: In order to develop ignition-proof magnesium alloys, the effect of alloying element Ce on the ignition-proof properties and surface tension of AZ91D-2.5Ca alloy were investigated. The results show that the addition of Ce can significantly raise the ignition temperature and change the structure of surface oxide film as well as the surface tension. When the Ce content increases to 1.2%, the ignition point reaches 1371K. Upon the addition of Ce, the oxide film of AZ91D-2.5Ca melt changes to fine and close structure from the porous structure before the Ce addition. The composite oxide film mainly composed of MgO, Al₂O₃, CaO and Ce₂O₃. The surface tension of AZ91D-2.5Ca decrease with the increasing Ce content, as the active-element Ce enriched at the melt surface.

Abstract: Recently, the computer technology, especially computer graphics, networks, multimedia, three dimensional simulation developments, injected virtual reality technology with new vitality, which also give 3D virtual scene a direction. The article mainly discusses technology of virtual building scenery, application in today's independent virtual building scene’s deficiency, and the integration of 3D virtual reality, locality and perspective advantages.

Abstract: The Mg-Ca-Ce ignition-proof Mg-alloy with high ignition temperature was developed based on the synergy of flame retardant role of Ca element and Re element ,and the flame retardant mechanism were investigated. The interfacial tension of Mg-Ca-Ce alloy melt was measured with the maximum bubble method. The interfacial tension is found to be remarkably lowered with the increase of Ce element that is a kind of surface active element to Mg-Ca alloy. The results also showed that the compact composite film composed of Ce2O3,CaO and MgO could be formed and reduce the flammability significantly when the Ca content and Re content were 1.2wt.% and 1.5 wt.% respectively, which prevented alloys from oxidation further and raised the ignition point nearly 150°C.

Abstract: This paper studied the effects of inclusion and slag on properties of a die cast A356 alloy wheel. The result showed that the rate of defect is important for the mechanical properties. The tensile strength and extension was not dropped but the rate of defect is increased about 2%. The variation trend of tensile strength and extension is linear, while the area of porosity on tensile fracture is between 2% and 6%. However, the tensile strength and extension was dropped with the increasing rate of defect. The variation trend of mechanical properties of the sample with inclusion is stable, but the sample with slag is not stable. The mechanical properties of samples with inclusion are drastically changed, while the rate of defect is increased. The mechanical properties of samples with slag are smoothly. The EDS analysis indicated that the defects consist of Al-Ti-B compound, α-phase (Al₁₂FeSi), β-phase (Al₉Fe₂Si₂) and Al₂O₃. These oxides form the compact composite oxide film expand into first cracks. The fracture mode of sample with defects is brittle fracture. The values of the Secondary dendrite arm spacing (DAS) in the inclusion and the matrix are the same, while the values of DAS in the slag and the matrix are different.

Abstract: Mg_72.5Zn₂₆Y_1.5 quasicrystal alloys were treated under different heat treatment process. The microstructures of the alloys were investigated. The quasicrystal and eutectic morphologies and their transformation during heat treatment process were detailedly studied. The results showed that lamellar and dendritic eutectic phases throughout the matrix were evidently formed under heat treatment process 310°C×30min water quenched and 310°C×30min liquid nitrogen deep cooling, respectively. Furthermore, quasicrystals of dragonfly-like and bulk polygon morphology were formed under heat treatment process 575°C×15min water quenched and 700°C×2min cooled with furnace, respectively. Various morphologies’ transformation mechanism during heat treatment process were also studied.

Abstract: Mg72.5Zn26Y1.5 quasicrystal alloys were investigated under different solidification conditions. The specimens of Mg-Zn-Y alloys with cooling rates from 13.2K/s to 69.8K/s were gathered by a designed multi-channel temperature acquiring system and then the microstructures and phase evolution of the alloys were analyzed. The results show that the precipitation temperature of icosahedral quasicrystal phase (I-phase) increased with cooling rate increased from 13.2 K/s to 69.8K/s. The microstructure was mainly made up of α-Mg, I-phase and Mg7Zn3 phase. Meanwhile, the quasi-crystalline morphology was significantly different in the experiments. It changed from five (six) petals to the big pentagon with the decreased cooling rate.