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Shang S.-Z.,East China University of Science and Technology | Lu G.-M.,East China University of Science and Technology | Tang X.-L.,East China University of Science and Technology | Zhao Z.-X.,East China University of Science and Technology | Wu C.-M.,Zhejiang Geely Automobile Research Institute Coltd
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2010

The 6061 semi-solid aluminium alloy feedstocks prepared by near-liquidus casting were compressed in semi-solid state by means of Gleeble-3500 thermal-mechanical simulator. The relationship between the true stress and the true strain at different temperatures and strain rates was studied with the deformation degree of 70. The microstructures during the deformation process were characterized. The deformation mechanism and thixo-forming properties of the semi-solid alloys were analyzed. The results show that the homogeneous and non-dendrite microstructures of semi-solid 6061Al alloy manufactured by near-liquidus casting technology could be transformed into semi-solid state with the microstructure suitable for thixo-forming which are composed of near-spherical grains and liquid phase with eutectic composition through reheating process. The deformation temperature and strain rate affect the peak stress significantly rather than steady flow stress. The resistance to deformation in semi-solid state decreases with the increase of the deformation temperature and decrease of the strain rate. At steady thixotropic deformation stage, the thixotropic property is uniform, and the main deformation mechanism is the rotating or sliding between the solid particles and the plastic deformation of the solid particles. © 2010 The Nonferrous Metals Society of China. Source

Zhang Z.,Tongji University | Zhao F.,Zhejiang Geely Automobile Research Institute Coltd | Deng J.,Tongji University | Li L.,Tongji University | Shen Y.,Zhejiang Geely Automobile Research Institute Coltd
Journal of Thermal Science and Technology | Year: 2013

The multiple injection strategies have been widely employed in many new diesel applications, such as HCCI (Homogeneous Charge Compression Ignition) and LTC (Low Temperature Combustion), which are very effective in improving fuel-air mixture and entrainment. In this paper, using high injection pressure of common rail and high-speed camera system, the experimental studies on the spray characteristics of the single, double and triple injections are conducted. The spray average fuel/air equivalence ratio is employed to evaluate the overall effects of the fuel-air mixture, which is the ratio of the fuel/air mass ratio in the spray and the fuel/air stoichiometric mass ratio. It is shown that the spray average fuel/air equivalence ratio decreased with the increased injection pressure, indicating that increasing injection pressure could intensify fuel-air mixture. For double injections, spray tip penetrations and volumes increase with the increased injected volume percentage. It is also found that spray development rate of the second injection is higher than the first injection. Double injections lead to lower spray average fuel/air equivalence ratios than the single injections. For triple injections, the spray average fuel/air equivalence ratios are almost lower than stoichiometry. The triple injection of which the volume distribution of every injection time is evenly has the lowest spray average fuel/air equivalence ratio, and has the best effect of fuel-air mixture. © 2013 by JSME. Source

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