Papers by Author: Yuan Yuan Li

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Authors: Yun Zhong Liu, Yuan Yuan Li
Abstract: In conventional studies, different empirical atomization equations are correlated for different kinds of atomization methods or even in the same method. In the present study, it was found that the basic law of melt breakup from bulky liquid into droplets can be universally applied to all atomization methods. Based on theoretical analysis, a new general equation of mean particle size applicable to both conventional atomization methods and new atomization processes is presented. The mean particle size in melt atomization is mainly controlled and decided by two key dimensionless parameter groups representing the liquid stability of melts and the breakup ability of atomizer respectively. Different specific atomization mechanisms result in different formulae in conventional atomization methods. In case of gas atomization, it is equivalent with and can be changed into Lubanska Equation. In case of centrifugal atomization, it can be changed into the equations that are currently the most widely used. In case of water atomization, it is similar to the equation proposed by Grandzol and Tallmadge. According to the universal equation, new correlations for mean particle size in novel atomization processes such as Hybrid Atomization and Multistage Atomization were proposed and agreed with our experimental data well.
Authors: Tungwai Leo Ngai, Da Tong Zhang, Yuan Yuan Li
Abstract: By choosing appropriate annealing temperature and annealing time, diffusion couples made of aluminum bronze and tool materials were prepared to simulate the diffusion and phase formation during the actual machining. These results were compared to those obtained from turning experiments. In agreement with results obtained from diffusion couple experiments, all turning experiments showed that major elements in both tool materials and workpiece diffused into their counterparts. The diffusion of C away from the tool will reduce the tool strength. It is helpful to use diffusion couple results to comprehend the diffusion effect in the actual turning process.
Authors: Tungwai Leo Ngai, Yuan Yuan Li, Zhao Yao Zhou
Abstract: Increasing density is the best way to increase the performance of powder metallurgy materials. Conventional powder metallurgy processing can produce copper green compacts with density less than 8.3g/cm3 (a relative density of 93%). Performances of these conventionally compacted materials are substantially lower than their full density counterparts. Warm compaction, which is a simple and economical forming process to prepare high density powder metallurgy parts or materials, was employed to develop a Ti3SiC2 particulate reinforced copper matrix composite with high strength, high electrical conductivity and good tribological behaviors. Ti3SiC2 particulate reinforced copper matrix composites, with 1.25, 2.5 and 5 mass% Ti3SiC2 were prepared by compacting powder with a pressure of 700 MPa at 145°C, then sintered at 1000°C under cracked ammonia atmosphere for 60 minutes. Their density, electrical conductivity and ultimate tensile strength decrease with the increase in particulate concentration, while hardness increases with the increase in particulate concentration. A small addition of Ti3SiC2 particulate can increase the hardness of the composite without losing much of electrical conductivity. The composite containing 1.25 mass% Ti3SiC2 has an ultimate tensile strength of 158 MPa, a hardness of HB 58, and an electrical resistivity of 3.91 x 10-8 Ω.m.
Authors: Zhi Yu Xiao, M.Y. Ke, Wei Ping Chen, D.H. Ni, Yuan Yuan Li
Abstract: The application of warm compaction in stainless steel powders has not been formally reported by now. In this paper, the warm compacting behavior of 316L stainless steel powders had been studied. Results showed that warm compaction was effective in improving the green density and strength of 316L stainless steel powders. Under the compacting pressure of 800 MPa, warm compacted density was 0.20 g/cm3 higher than cold compacted one, and green strength was 52% higher. The optimum warm compacting temperature was 110±10°C. With die wall lubricated warm compaction, the internal lubricant content can be reduced by 0.5 wt%.
Authors: Li Fa Han, Wei Xia, Yuan Yuan Li, Wei Ping Chen
Abstract: This paper presents an investigation on the surface roughness of burnished hypereutectic Al-Si alloy ¾ a widely used light-weight and wear resistant material in automobile, electric and aircraft industries. Based on the techniques of Taguchi, an orthogonal experiment plan with the analysis of variance (ANOVA) is performed and a second-order regressive mathematical model is established. Meanwhile, the influence of process parameters on surface roughness and its mechanism are discussed. From the experiments, it is found that burnishing process is effective to decrease surface roughness of hypereutectic Al-Si alloy components, in which, all input parameters have a significant effect on the surface roughness. To achieve a small surface roughness, the optimum process parameters are recommended.
Authors: Zhi Xin Kang, Yuan Yuan Li, Kunio Mori
Abstract: An organic compound of dihexyl-contained triazine dithiol was specially synthesized for surface modification of magnesium alloy AZ91 in order to improve its corrosion resistance. The nano-scale polymer film on the surface of AZ91 was created with the synthesized compound by means of electrochemical measuring system called as polymer plating in the electrolytic solution. The modified surface of AZ91 had the peculiar functional characteristic of water repellency to inhibit corrosion. Corrosion tests were carried out with methods of polarization curve and electrochemical impedance. The corrosion resistance was evaluated from corrosive current density and reactive resistance. When concentration of the compound was set on 8 mol/m3, the good corrosion resistance was obtained for low corrosive current density and high reactive resistance in NaCl aqueous solution at 303K.
Authors: Wei Wen Zhang, Hai Dong Zhao, Ji Xiang Gao, Yuan Yuan Li
Abstract: Double-stream-pouring continuous casting (DSPCC) is a novel technique to prepare gradient composites. In this paper, a two-dimensional steady mathematical model coupled flow, heat and solution transport in the solidification zone of DSPCC has been established based on the standard k-ε turbulent model. The variation of thermo-physical properties of the alloys against the temperature is also considered. The effects of casting speed on the temperature field, velocity field and composition of the researched composite are analyzed based on the proposed mathematical model. An experimental 2024/3003 aluminum composite was prepared by using a laboratory-made DSPCC facility. Selected results of experiment are in a good agreement with that of numerical simulation.
Authors: Sheng Guan Qu, Yuan Yuan Li, Wei Xia, Wei Ping Chen
Abstract: An apparatus measuring changes of various forces directly and continuously was developed by a way of direct touch between powders and transmitting force component, which can be used to study forces state of powders during warm compaction. Using the apparatus, warm compaction processes of iron-based powder materials containing different lubricants at different temperatures were studied. Results show that densification of the powder materials can be divided into four stages, in which powder movement changes from robustness to weakness, while its degree of plastic deformation changes from weakness to robustness. The proposed densification mechanism may provide an insight into understanding of warm compaction process.
Authors: Zhi Xin Kang, Wei Ping Chen, Yan Long, Kunio Mori, Yuan Yuan Li
Abstract: A novel technique was developed for direct joining between ethylene propylene rubber and high ductile spheroidal-graphite cast iron using functional polymeric nanofilm without any adhesive. The functional polymeric nanofilm was created on the surface of cast iron by means of polymer plating with a synthesized organic compound of 6-diallylamino-1,3,5-triazine-2,4-dithiol monosodium salt. High peel strength joints of the rubber to polymer-plated cast iron were achieved by adding an accelerating agent of perhexane 3M under crosslinking condition of 418 K for 7 min. As the thickness of polymeric nanofilm was around 8.5 nm, peel strength of the joints was high to 8.9 kN/m and its broken-out section was rubber cohesive failure with 100% rubber coverage. Rubber/cast iron joints possessed good heat-resistant property. The film thickness and perhexane content had large effects on water resistance of joints. It is considered that high joining property results from chemical bond at interface between polymer-plated cast iron and rubber chain.
Authors: Zhi Xin Kang, Yuan Yuan Li, C.W. Zhong, Ming Shao, Wei Xia
Abstract: The nanoscale functional thin film with the affinity to acrylic rubber was formed on the surface of a high ductile spheroidal-graphite cast iron by means of polymer plating of 6-diallylamino-1,3,5-triazine-2,4-dithiol monosodium salt. The direct joining of acrylic rubber to the cast iron was achieved with the functional nanofilm during curing. High peel strength adherend of the rubber/cast iron was obtained with suitable film thickness and good film quality under curing at 453 K for 18 min. When the film thickness was 8.53 nm, peel strength of the adherend was high to 4.9 kNm-1, and its broken-out section was rubber cohesive failure. The film thickness considerably affected peel strength and rubber coverage. Moreover, the current density of polymer plating had largely influence on mass and quality of thin film, thereby on joining property of acrylic rubber to the cast iron. The good joining property results from chemical bond within interfacial layer of acrylic rubber chain and reactive groups of nanofilm polymer-plated on the surface of cast iron.
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