Papers by Author: Zhi Feng Wang

Abstract: Monolithic uniform nanoporous Cu (NPC) ribbons with a ligament/pore size of 10-25 nm are successfully synthesized by chemical dealloying the Cu₅₀Zr₅₀ and Cu₅₀Zr₄₅Al₅ metallic glasses in 0.5 M HF for 7 min. It is found that the length scale of ligaments/channels can be tuned by simply alloying 5 at.% Al to the Cu-Zr binary glassy alloys. The current signal of the NPC-supported MnO₂ composite electrode is remarkably enhanced as compared to that of pure MnO₂ powders. These new findings greatly raise the hope for possible applications of NPC as a new type of electrode substrates or an advanced sensor in green and new energy technology.

Abstract: Thermodynamics and dynamics of Mg3Zn6Y quasicrystals in solidification process were detailedly studied in this paper. The free energy, nucleation rate and nucleation energy were deduced and calculated. It shows that the driving force and nucleation rate gradually increase with the decreased temperature. The further studies show that the nucleation energy increase gradually with the decreased liquidus temperature. And it is apt to quasicrystal nucleation by increasing the cooling rate in a proper temperature range.

Abstract: This paper studied the effect of Mg-Nd alloys on the ignition-proof performance of AZ91D magnesium alloy. The results showed that 0.5%Nd decreased the ignition point of alloy for about 20°C, but the ignition point could been multiplied with the adding of Nd element. When the content of Nd reached 5%, the ignition point increased about 40°C compared with AZ91D alloy. The ignition point reduced after the addition of 0.5%Nd can be attributed to the decrease of the solidus temperature and liquidus temperature. The further analysis indicated Nd and Al formed Al3Nd first, which consumed the content of Nd, so that the alloy didn’t have enough Nd to form Nd2O3 to protecting the alloy. The EDS analysis indicated when the addition of Nd reached 5%, competent Nd2O3 could be formed and compact oxide film which consisted of Nd2O3, MgO and Al2O3 was formed to prevent alloys from oxidation and combustion.

Abstract: Using Al powder as thickening agent and CaCO3 powder as foaming agent, Al foams with above 85% porosity, pore sizes between 1mm and 4mm and relatively uniform pore structure have been fabricated by melt foaming method at different foaming temperatures. Meanwhile, the paper researched the effect of foaming temperature on foaming effect and analyzed the defects in Al foams. At last, compression test were taken in order to investigate the mechanical properties of aluminum foams. The results showed that pore structure, pore distribution and compression properties of Al foams fabricated at 720°C were much better than that fabricated at lower temperature.

Abstract: The paper studied various morphologies of the quasicrystal phase in Mg-Zn-Y alloys caused by different cooling rates. The cooling rates were reached through five kinds of cooling media. The cooling curves were monitored by multichannel data acquisition cards. A further heat treatment was made to study quasicrystal growth behavior. The results showed that, with the decrease of cooling rate, the quasicrystal morphology changed and its size became larger. Moreover, a planar quasicrystal morphology evolution schematic diagram during quasicrystal growth process was observed for the first time.

Abstract: The tube-shaped parts of A356 alloy were deformed from 0% to 83% by spinning process. The microstructure and mechanical properties of A356 alloy were discussed. The results showed that as the wall thickness reduction increases, the dendrite cells of cast alloy are lengthened gradually and the average Secondary Dendrite Arm Spacing (SDAS) is reduced from 37.2μm to 23μm and eutectic silicon particles are distributed orderly along the spinning direction. The coarse acicular β-Al5FeSi is broken into many sections, and its length is reduced from 37.5μm to 12.5μm in the cross-section. The tensile strength and elongation exhibit a strong dependence upon the variation in wall thickness, with a parabolic relationship. The tensile fractured surface of parts with deformation ratio above 35% exhibits many equiaxial dimples, with intergranular ductile fracture mode.

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.

Abstract: Mg72.5Zn26Y1.5 (at.%) quasicrystal alloys were investigated under different solidification conditions. The cooling curves were gathered by the multi-channel temperature acquiring system and the corresponding microstructures were analyzed. The morphology, microhardness and volume fraction of quasicrystals were detailedly studied. The effects of cooling rate on the above three aspects were also studied and the relation schema among them were exhibited. The results show that the quasicrystal size tend to smaller, its microhardness and volume fraction gradually increased, and the quasicrystal morphology changed from bulk polygon to petal-like and finally changed to plat X-shape with the elevated cooling rate from 2.3K/s to 181.2K/s. However, the quasicrystal nucleation will be restrained and amorphous matter will be created if the cooling rate exceed the critical point which make against the formation of quasicrystals with high performance.