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Ni C.,Tsinghua University | Lu G.,Suzhou Mingzhi Technology Co. | Jing T.,Tsinghua University | Wu J.,Tsinghua University
Powder Technology | Year: 2017

The flow behavior of sand particles during the core shooting process has been studied by combination of computational fluid dynamics (CFD) simulations and experiments. In the CFD simulations, a two-fluid model (TFM), in which a kinetic-frictional constitutive correlation is incorporated, has been applied to describe the flow dynamics of core shooting process. The influences of turbulence model and boundary conditions on the modeling of core shooting process are further investigated. The simulation results indicate that there are certain sensitivities to the wall boundary condition in the sand flow behavior while no significant difference is observed between the results of the laminar and turbulence models. Using high-speed photography system and pressure measuring system, systematic experiments have been carried out to fully validate the model and good agreement is obtained between simulations and experiments. Based on the simulation and experimental results, the flow behavior of sand particles in the core box is analyzed, and the effects of nozzle dimension (D = 6, 8, 10, 15 mm) and shooting pressure (Pin = 0.3, 0.4, 0.5 MPa) on the hydrodynamic properties such as sand particle mass flux, sand volume fraction at the nozzle and distribution of sand velocity are discussed. © 2017 Elsevier B.V.


Zhang Z.-J.,Jiangsu University | Si N.-C.,Jiangsu University | Sun S.-C.,Jiangsu University | Liu G.-L.,Jiangsu University | Wu Q.-F.,Suzhou Ming Zhi Technology Company Ltd
Zhongguo Youse Jinshu Xuebao/Chinese Journal of Nonferrous Metals | Year: 2012

The casting silumin ZAlSi7Cu4 that was treated with different technologies for heating processing was used to make a thermal cycle experiment at 20↔300°C, 20↔350°C and 20↔400°C, respectively, on a self-restrict thermal fatigue experimental machine. The effect of thermal fatigue property caused by different technologies for heating processing and the effect of crack growth caused by different temperature breadths were studied. Optica1 microscopy (OM) and scanning electron microscopy (SEM) were used to examine the damage mechanisms of thermal fatigue. The results show that the sample with T6 treatment has better property than other two kinds of samples. The expansion path of crack can be influenced by the location of grains. With the increase of the maximum temperature, the lifespan of three kinds of alloys will decrease when the minimum temperature is fixed. In the interval of 300-350°C, the temperature sensitivity of the alloy is higher than that in the interval of 350-400°C when the minimum temperature keeps at 20°C.


Zhang Z.,Jiangsu University | Si N.,Jiangsu University | Liu G.,Jiangsu University | Sun S.,Jiangsu University | Wu Q.,Suzhou Mingzhi Technology Company Ltd
Tezhong Zhuzao Ji Youse Hejin/Special Casting and Nonferrous Alloys | Year: 2012

The thermal cycling curves of ZAlSi7Cu4 treated by different heat treatment were drawn on a self-restrict thermal fatigue experimental machine at 25-350°C to understand the effect of different heat treatment processes on the thermal fatigue behavior of the alloy. The thermal fatigue mechanism was analyzed by observing thermal fatigue crack morphology of the alloy samples with the help of OM (optical microscope) and SEM (scanning electron microscope). The results show that the sample with T6 heat treatment is superior to one treated by other process in thermal fatigue resistance at 350°C The expansion path of the crack can be controlled by the location of the grain, and the crack generation in the edge of the cavern can be slowed down with a higher curvature radius. The micro-hardness of the sample surface is decreased with the increase of the thermal cycle number, however, the microhardness of the samples treated by T6 and as-cast quenching plus aging has a slightly ascension in the period before the initiation of the crack.


Zhang R.H.,Jiangsu University | Ma D.X.,Jiangsu University | Sun S.C.,Jiangsu University | Mao J.Z.,Suzhou Mingzhi Technology Co.
Manufacturing and Engineering Technology - Proceedings of the 2014 International Conference on Manufacturing and Engineering Technology, ICMET 2014 | Year: 2015

Some leakage problems are found in some casting aluminum alloy heat-exchangers which are produced by core assembly molding and low pressure casting during gas tight test. In order to know the reasons that lead to the leakages, the defects and microstructure of the leakage positions are observed by MM6 metallographic microscope and compared with those of sound positions in the same heat exchanger. According to the observation and contradistinction, a consequence was achieved that it is the interaction of shrinkage porosities, gas-shrinkage porosities and microporosities that lead to the leakages. Some control measures are proposed on the base of this consequence to avoid these leakage defects. © 2015 Taylor and Francis Group, London.


Liu G.-L.,Jiangsu University | Si N.-C.,Jiangsu University | Sun S.-C.,Jiangsu University | Wu Q.-F.,Suzhou Mingzhi Technology Ltd.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2014

Al-7.5Si-4Cu cast alloy melt modified by Al-5Ti-B, RE and Al-10Sr master alloys were poured in the chromite sand moulds, to investigate comparatively the effects of individual or combined additions of grain refiners and modifiers on the mechanical properties, microstructures, grain refining and modification, and intermetallic compounds of the alloy. The results show that the mechanical properties and the microstructures of Al-7.5Si-4Cu cast alloys are improved immensely by combining addition of 0.8%Al-5Ti-B, 0.1%RE and 0.1%Al-10Sr grain refiners and modifiers compared with the individual addition and cast conditions. For individual addition condition, addition of 0.8% Al-5Ti-B master alloy can obtain superior tensile strength, Brinell hardness and finer equiaxed α(Al) dendrites. The alloy with 0.1% RE master alloy shows the highest improvement in ductility because the rare earth can purify the molten metal and change the shape of intermetallic compounds. While the alloy with 0.1% Al-10Sr modifier shows only good improvement in yield strength, and the improvement of other performance is unsatisfactory. The Al-10Sr modifier has a significant metamorphism for the eutectic silicon, but will make the gas content in the aluminum alloy melt increase to form serious columnar grain structures. The effects of grain refining and modification on mean area and aspect ratio have the same conclusions obtained in the mechanical properties and the microstructures analyses. © 2014 The Nonferrous Metals Society of China.


Wang W.-H.,Jiangsu University | Si N.-C.,Jiangsu University | Liu G.-L.,Jiangsu University | Wu Q.-F.,Suzhou Mingzhi Technology Company Ltd
Zhuzao/Foundry | Year: 2012

In order to study the influence of heat treatments on the comprehensive mechanical properties of multiple Al-Si alloy, the alloy specimens in the state of as-cast, water quenching+aging treatment and aging treatment, were carried out in testing machine of 3000 kN, the microstructures of the alloy were analyzed by the optical microscope and SEM, then the mechanical properties were tested. The results show that, the mechanical property of the multi-component Al-Si alloy treated by as-cast water quenching+aging is the best among the three states, and then the aging treatment, the mechanical property of as-cast is the worst. For as-cast water quenching is equivalent to a transient solution treatment, dispersed phases (Al 2Cu, Mg 2Si and θ′ phases etc.) would integrate into α solid solution in the solution treatment, then separated out in the aging treatment, which drastically improved the mechanical properties of the alloy.


Liu G.,Jiangsu University | Si N.,Jiangsu University | Sun S.,Jiangsu University | Zhang Z.,Jiangsu University | Wu Q.,Suzhou Mingzhi Technology Ltd.
Jinshu Xuebao/Acta Metallurgica Sinica | Year: 2013

With the rapid development of automotive industry, the requirements for engine performance has become increasingly higher and higher, such as dynamic performance, environmental performance, fuel economy performance and so on. Obviously, using lighter aluminum engine has become the future of the automobile industry. When start or stop the engine, the engine generates drastic temperature field that will make parts of the engine components into the plastic deformation zone. If the engine components continue like this, extremely high thermal strain will cause the thermal fatigue failure of aluminum alloy for automotive engine. Thermal fatigue is a more serious form of material fatigue failure. The thermal fatigue is prevalent in many important engine castings, such as cylinder body, cylinder head, piston and so on. Therefore, study on thermal fatigue properties of multivariate Al-Si-Cu cast alloy has the most important significance. Based on this thermal fatigue behaviors of multivariate Al-7.5Si-4Cu alloys under different heat treatment were investigated in the temperature ranges of room temperature to 350°C. The thermal fatigue cracks of the tested specimens were observed using OM and SEM. The results demonstrate that thermal fatigue properties of the alloy after T6 heat treatment is better than the alloy after cast-quenching+aging heat treatment and the cast alloy. Reasonable heat treatment process can improve the strength, the plasticity and the thermal fatigue property of multivariate Al-7.5Si-4Cu alloy, including reduce the rate of crack propagation. The main reason of crack initiation is oxidative microstructure induced by thermal stress. Fatigue crack expands along the grain boundary by passivation-sharpen of crack tip in the early. In the late, fatigue crack expands with both intergranular way and transgranular way by passivation-sharpen of crack tip and siamesed holes on front edge of crack tip. The Si phases can affect fatigue crack propagation. When the angle between the fatigue crack propagation and the short axis of the Si phase is more than 60°, fatigue crack expands as "bypass-wall expansion". When the angle between the fatigue crack propagation and the long axis of the Si phase is more than 60°, fatigue crack expands as "through-wall expansion". Oxidation behavior effects significantly at the crack initiation period. After T6 heat treatment, the antioxidant property of multivariate Al-7.5Si-4Cu alloy is the best. Oxidation kinetics curves of multivariate Al-7.5Si-4Cu alloy under the different heat treatment are all logarithmic relationship. © Copyright;.


Liu G.L.,Jiangsu University | Si N.C.,Jiangsu University | Sun S.C.,Jiangsu University | Shu H.J.,Jiangsu University | Wu Q.F.,Suzhou Mingzhi Technology Ltd
Materials Research Innovations | Year: 2013

The effects of heat treatments on the microstructure and dry sliding friction and wear performance of Al-7·5Si-4Cu alloy were studied in this paper. The results indicated that after T6 treatment, the grains of the α-Al phase and eutectic structure were evenly distributed with increase in grain number, reduction in defects, and Si phase morphology tending round. In addition, A12Cu phase and AlMnFeSi phase precipitated interdependently in clumps or granular shape. Under lower load of 100 N, the wear loss of three alloys added slowly with increasing load, and the dominant wear mechanism was abrasive wear accompanied by slight adhesive wear. Especially, the alloy after water quenching plus aging treatment possessed the highest wear resistance. Under higher load of 300 N, the wear mechanism was delamination wear and abrasive wear for as cast alloy, serious adhesive wear and abrasive wear for alloy with water quenching plus aging treatment and abrasive wear accompanied by adhesive wear for alloy after T6 treatment. © W. S. Maney & Son Ltd. 2013.


Shu H.-J.,Jiangsu University | Si N.-C.,Jiangsu University | Sun S.-C.,Jiangsu University | Liu G.-L.,Jiangsu University | Wu Q.-F.,Suzhou Ming Zhi Technology Company Ltd
Zhuzao/Foundry | Year: 2011

The influence of AlTi 5B 1 content on microstructure and mechanical properties of hypoeutectic Al-Si alloy was studied. The results show that the AlTi 5B 1 content exerts a greater influence on the tensile strength of alloy and when Ti reaches 0.06wt.%, the tensile strength reaches its maximum. The influence of AlTi 5B 1 content on elongation is similar to tensile strength. AlTi 5B 1 content has a smaller effect on the hardness of alloy. After inoculation with AlTi 5B 1 the quantity of TiB 2 and Ti(A1 1-x, Si x) 3 as effective nucleation cores increases, which play a major role in the refinement. The morphologies and distributions of second-phase (Fe phase, AlCu phase) change, which intensifies grain boundary and weakens Fe phase's negative action.


Liu G.L.,Jiangsu University | Si N.C.,Jiangsu University | Sun S.C.,Jiangsu University | Wu Q.F.,Suzhou Mingzhi Technology Ltd
Materials Research Innovations | Year: 2013

The effects of different mould sands and casting wall thicknesses on the properties and microstructures of multivariate Al-7·5Si-4Cu alloy, which was modified by Al-10Sr, RE and Al-5Ti-B master alloys, were investigated. The melt was poured into multistep moulds made from three mould sands (quartz, alumina and chromite) to produce specimens for mechanical property testing and metallography. The results demonstrated that the sample with chromite sand exhibited the best mechanical properties owing to its higher cooling rate. Tensile strength and elongation decreased monotonically with increasing wall thickness. No obvious trend of wall thickness on hardness of the alloy was found. When the cooling speed decreased, the grain refinement and transformation effect became weaker, the dendrite arm spacing (DAS) increased obviously and the properties and microstructures became poorer. A series of fitting models was established and used to predict properties of Al-7·5Si-4Cu alloy from the DAS. © W. S. Maney & Son Ltd. 2013.

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