Papers by Keyword: Semi-Solid

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Authors: Annalisa Pola, Roberto Roberti, Ermanno Bertoli, Disman Furloni
Abstract: Semi-solid processing is nowadays a powerful technology for the realization of structural components; in addition to the increase in their mechanical properties, due to the globular structure instead of the dendritic one, further developments are most likely to be expected from alloy chemical composition adjustments in order to achieve higher performances compared with the industrially used A356 and A357. Aim of this research is to try to set up new aluminium alloys for semisolid foundry applications, starting from the standard Al-Si system, at the base of all known casting processes. Different chemical compositions, based on either foundry or wrought Al alloys, have been investigated by means of computational thermodynamics (Pandat®), producing quantitative data about solidus-liquidus interval, solid fraction as a function of temperature, phase diagrams i.e. potential for age hardening, etc.. Some selected alloys, fitting the needs of good castability, proper concentration of hardening elements in the alpha phase and, obviously, easy production of feedstock material have been mechanically stirred by means of an experimental apparatus designed and self-constructed in the foundry laboratory of the university; the effect of different stirring tool configurations on the semi-solid state obtainment has also been assessed. Subsequently, the manufactured alloys have been reheated and cast into a simple die, properly designed, for the production of small samples. Microstructural investigations have been done on the stirred alloy (before and after re-heating), on the as cast and the heat treated samples to evaluate the efficiency of the designed system and of the defined alloys. Experimental tests on the processed alloys have been carried out by means of an instrumented crucible in order to verify the predicted thermodynamic properties supplied by simulation study (i.e. fs-temperature curve).
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Authors: Guo Chao Gu, Raphaël Pesci, Eric Becker, Laurent Langlois, Régis Bigot
Abstract: It is necessary to well understand the microstructure evolution during high speed heating and forming for steel thixoforging, since it determines the thixotropic flow behavior of materials in the semi-solid state. A new in situ technique - high temperature Confocal Laser Scanning Microscopy (CLSM) - was developed and used for studying the microstructure evolution directly at high temperature where the microstructure in the semi-solid state could not be preserved by quenching experiments for conventional 2D characterization. Several steel grades (C38LTT, 100Cr6 and M2) were investigated during heating from the as-received state to the semi-solid state and finally cooled to the solid state).It has been found that there is a significant difference in diffusion rate of alloying elements between these grades during heating and cooling. In M2, thanks to the high content of alloying elements and their low diffusion rate, the semi-solid temperature range is greater and its microstructure in the semi-solid state could be preserved by quenching or even at a low cooling rate, which means the microstructure of M2 in the semi-solid state can be characterized in room temperature on quenched M2 samples. On the contrary, the microstructure of other steel grades 100Cr6 and C38LTT in semi-solid state can only be revealed by CLSM at high temperature because of the lower volume fraction of alloying elements and their high diffusion rate. It is very interesting to use high temperature CLSM to in situ investigate the microstructure evolution in the semi-solid state, especially at low liquid fraction.
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Authors: Chen Yang Zhang, Sheng Dun Zhao, Guan Hai Yan, Yong Fei Wang
Abstract: To prepare semi-solid AlSi9Mg alloy slurry, we simulated electromagnetic stirring (EMS) based on a coupled 3D model of electromagnetic field, temperature field, and flow field by sequentially coupling ANSOFT and FLUENT software. Results show that magnetic flux density and electromagnetic body force (EMF) decrease and exhibit non-uniform patterns as stirring frequency increases. However, magnetic flux density and EMF increase in proportion to the stirring current but become more inhomogeneous. As EMF increases, the flow velocity and the depth of vortex in the semi-solid slurry gradually increase; thus, slurry temperature decreases. The deviation in temperature is then reduced between the center and the edge. As a result, the microstructure of the slurry evolves from coarse rosette grains to fine and spheroidal ones. By comparison, turbulent flow is generated by excessive and more unevenly distributed EMF, which causes deterioration in microstructures, such as the formation of cavities in the semi-solid AlSi9Mg alloy slurry. Based on simulation and experimental results, our conclusion is that reasonable process parameters have been obtained and verified experimentally. These results also show the validity and reliability of EMS-prepared semi-solid AlSi9Mg alloy.
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Authors: Meng Ou Tang, Jun Xu, Zhi Feng Zhang, Yue Long Bai
Abstract: Annular electromagnetic stirring (A-EMS) process is an advanced semi-solid metal processing technology. It could avoid the effect of skin effect, increase the shear rate, reduce the temperature gradient and refine microstructures. A three-dimensional computational model sequentially coupling electromagnetic stirring with a macroscopic heat and fluid flow in A357 alloy semisolid slurry preparation by A-EMS has been developed. Comparison between microstructures of A357 alloy produced by EMS and A-EMS has been made. The results show that the annulus gap avoids the part of low magnetic induction intensity and A-EMS avoids the effect of skin effect. The annulus gap prohibits the circular flow and increases the shear flow. The circular flow is more effective than the shear flow on heat dissipation. A lower temperature difference in the stirred melt and subsequent uniformly fine microstructures were obtained as compared with the normal electromagnetic stirring.
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Authors: Zheng Liu, Wei Min Mao
Abstract: The semi-solid A356 alloy slurry is prepared by compound process, and the effect of the compound process on morphology and size of primary α-Al in A356 alloy is researched. The results indicate that the compound process remarkably affects the morphology and the size of primary α-Al. Primary α-Al with particle-like is distributed uniformly in A356 alloy, and there is no the transient area of change in structure morphology. Compared with the samples prepared by low superheat pouring and slightly electromagnetic stirring, the nucleation rate, morphology and grain size of primary α-Al in A356 alloy are markedly improved by the compound process. The mechanism of refining grain in the compound process is probed.
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Authors: Michael Modigell, Torsten Volkmann, Christoph Zang
Abstract: Rheometrical analysis of steel slurries in rotational rheometers requires a range of operating temperatures of about 1300 to 1600 °C, leading to a delicate device-related challenge with respect to the applied materials on the one hand and a suitable constructional set-up gaining unbiased measurements on the other hand. Accordingly, a new high-precision rotational rheometer for temperatures up to 1700 °C has been developed as an improvement on an existing rheometer previously developed at the Chair of Mechanical Process Engineering (AVT) of RWTH Aachen University. First measurements on the tool steel X210CrW12 in the mushy state with solid fractions of 20% to 40% demonstrate a remarkable improvement on the preciseness of torque gain which broadens the area of possible experimental operations on steel slurries in order to reliably characterize transient behavior of the material by e.g. creep, relaxation and oscillation experiments.
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Authors: Song Yang Zhang, Rui Zhang, Xing Zhang, Cheng Cheng Wang
Abstract: Metal ceramic composite are adding ceramic particle powder to metal, also called powder dispersion reinforced materials, Its unique properties with extensive use value. But how to produce the metal ceramic composite is the main diffculty of the technology. In the last the method of the mixing are mechanical mixing method ,electromagnetic stirring and so on .The shortcomings of mechanical mixing method is clunky, difficult operation and low efficiency. The problem of the electromagnetic stirring method is its large equipment investment and its complex device. The paper researched a new device to produced metal ceramic composite in the semisolid process which advangtage is self-quantitative ,uniform mixing,save energy and environmental protection.This device was designed in sample full consideration of the mixing process may. As much as possible to avoid cracks. As to the sealed containers to consider the nitrogen let liquid to prevent oxidation and reduce the impurity intervention; Another auxiliary handle design also to make the experiment more convenient and accurate Indeed, etc. These advantages are the practicability for device, and provide a guarantee for the production metal ceramic composite.
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Authors: H. Meidani, S. Hossein Nedjad, Mahmoud Nili-Ahmadabadi
Abstract: A new process for fabrication of semisolid billets is introduced, which involves equal channel angular pressing and isothermal heating in the semisolid state. The process leads to a relatively fine globular microstructure. The microstructure evolution during isothermal treatment is studied and it is shown that dendrites breaking up has happened during equal channel angular pressing in semisolid state. The microstructural evolution during isothermal heating and the mechanism for the formation of the globular structure is tried to be understood and also modeled.
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Authors: Xiang Wang, Tong Zhao, Di Tie, Ren Guo Guan
Abstract: A novel process for grain refining and manufacture of high quality semisolid slurries ofalloys was developed. The process was proven to refine metal grain remarkably, and the grain sizeof pure aluminum can be refined to the first grade of Chinese refining standard of pure aluminumGB/T 7946.4-1999 ref) . P rimary silicon and eutectic silicon in the hypereutectic Al-Si alloy can bealso effectively refined. This process was used to prepare the billets with small spherical grains orequiaxed grains of Al-6Si-2Mg, AZ91, AZ31 and hypereutectic Al-Si alloys successfully. The p ip es ,profi le s and wire s of 6201, AZ31 and AZ61 alloys were produced by continuous rheo-extrusion.The strips of AZ91, AZ31, and Mg-Sn alloys were prepared by rheo-rolling. As an innovativeprocessing technology with low cost and high efficiency, vibrating sloping plate melt treatment hasgood prospective application in many fields such as rheo-casting, rheo-extrusion, rheo-rolling,metal microstructure refinement, etc.
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