Papers by Keyword: Primary Silicon

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Authors: Guang Hui Qi
Abstract: In order to settle environment pollution and provide a high effective and low-cost modifier for refining the primary Si in hypereutectic Al-Si alloys, Al-Fe-P master alloys containing 2.0~5.0% phosphorus have been invented by casting method. The Al-Fe-P master alloys can be conveniently produced and an excellent modification can be obtained by adding 0.3~0.8wt% Al-Fe-P master alloy in Al-Si alloys containing 12%-25% Si at a relatively lower modifying temperature. The number of primary Si increases obviously and the average grain size of primary Si decreases largely, less than 50μm. Furthermore Al-Fe-P master alloys have many advantages, such as low cost, convenient operation technology, no pollution, stable and long-term modification effect, easy storage and etc. Al-Fe-P master alloys have overcome the shortages of current modifier and have a good future for hypereutectic Al-Si alloy modification.
Authors: Sergey Komarov, Yasuo Ishiwata, Yoshihiro Takeda
Abstract: The present work introduces a novel ultrasonic DC casting process which allows producing billets of hypereutectic Al-Si alloys with greatly refined and uniformly distributed particles of primary Si. In the process, ultrasonic vibrations are introduced into an Al-17Si-0.01~0.03P melt in a hot top positioned on the mold by using a high-amplitude ceramic sonotrode. The hot top design and sonotrode arrangement provided a highly effective cavitation treatment of the melt in the hot top and well-controlled flow in the sump. A simplified model is proposed to explain the obtained results.
Authors: Ju Young Cho, Bok Hyun Kang, Ki Young Kim
Abstract: Various metallurgical refining processes of SOG (Solar Grade)-Si are being developed aiming its cost reduction for the PV (Photovoltaic) market. High purity silicon can also be obtained from Al-Si alloys using solidification theory. Since the solubility of impurity elements in silicon decreases rapidly with temperature decrease much above the Al-Si eutectic temperature, the removal of impurities from silicon at low temperature is expected to be effective. Most of impurity elements with small segregation coefficient can be removed during solidification. Key technology in this process is to separate the primary solid silicon from the liquid eutectic matrix during solidification. Some methods by an electromagnetic force or by combining flocculation and filtration techniques have been proposed to separate the solid silicon. The present study describes a new way to extract the primary silicon crystal from Al-Si alloys using centrifugal force during solidification for a silicon solar feedstock. Primary silicon was separated in the shape of foam during solidification, and pure Si flakes after acid leaching could be obtained.
Authors: Ke Zhun He, Fu Xiao Yu, Da Zhi Zhao, Liang Zuo
Abstract: The hot deformation behavior of DC cast phosphorous modified and unmodified hypereutectic Al-Si alloys was studied in the temperature range of 400-500 °C and strain rate range of 0.001-1 s-1. Processing maps were developed to evaluate the efficiency of the hot deformation and to identify the instability region. The results show that the peak stresses of the unmodified alloy are higher than that of the modified alloy at the strain rate of 1 s-1 and temperatures of 400 and 440 °C. The maximum power dissipation efficiencies for both the alloys are in the region of T=480-500 °C and =0.01-0.1 s-1. The flow instabilities for both the alloys occur in regions of high strain rate about 1 s-1 and temperature about 400 and 500 °C. The instability region area of the unmodified alloy is larger than that of the modified alloy. In addition, the primary Si cracking frequencies of the unmodified alloy are higher than that of the modified alloy when compared at the same deformation rate and temperature. The coarser primary Si particles of the unmodified alloy cause higher stress concentration around them when deformed at low temperature and high strain rate.
Authors: Hong Zhang Deng, Qiu Lin Li, Ding Guo Yang, Wei Liu
Abstract: Alternating traveling magnetic field (TMF) was introduced to agglomerate the inclusions with a density smaller than surrounding melt. Primary silicon particles precipitating from the solidification process of hypereutectic Al-Si alloy was regarded as inclusions need removing. Results indicated that alternating TMF was more effective to promote the inclusions to agglomerate into clusters than downward TMF. The effect of alternating TMF to agglomerate the inclusions increases with the increase of current and frequency. There exists the best alternating time to get the best agglomeration effect. In this study, 10s is the best alternating time.
Authors: Xiao Song Li, An Hui Cai, Ji Jie Zeng
Abstract: The influence of Fe on microstructure and the expansion coefficient and thermal conductivity of Al-30 wt.% Si alloy was studied. Results show that the primary silicon morphology and size changed significantly after joining the Fe, by angular blocky primary silicon sheet or plate into small pieces and then into a polygonal large lump, edge and angle are passivated. As the content of Fe is 0.3 wt.%, material expansion coefficient and high thermal conductivity. Later, with the increase of the content of Fe, alloy point defect and line defect, surface defect and large area defect increase, the thermal conductivity of materials and inflation performance declined. When the content of Fe is 0.1 wt.%, materials with high thermal conductivity and low thermal expansion coefficient, the heat storage performance impact is minimal.
Authors: Ke Qin, Jian Zhong Cui
Abstract: The influences of low frequency electromagnetic field on microstructures and macro-segregation in direct chill casting process were investigated in the experiments,Al-19.2%Si alloys were semi-continuously cast into ingots with 100 mm in diameter. Microstructures and macrostructures of samples taken from different part of the cast with different electromagnetic field conditions were characterized by optical microscopy. The results showed that low frequency electromagnetic field refines the microstructures and reduces macro-segregation. Unlike casting without electromagnetic field, the primary Si grains were homogeneous with fine dimensions and the morphology of the primary silicon exhibited small blocky structures or near-spherical structures. Further more, decreasing frequency is beneficial to the improvement. In the range conditions in the experiments, the optimum frequency is found to be 15Hz. During casting, the temperature of the liquid metal in the sump was monitored. The results shown, under LFEC the width of the liquid-solid region became narrowed and the temperature field in the sump also became homogeneous.
Authors: Wei Xi Shi, Cheng Wu Du, Bing Liu, Ping Yuan Wang
Abstract: The modification mechanism of hypereutectic Al-17.5%Si alloy with Nd was studied by OM and XRD. The results of OM analysis show that pure Nd could effectively refine primary in hypereutectic Al-17.5%Si alloy. When Nd addition is 0.3%, the average grain size of primary silicon reaches its minimum. The average grain size of primary silicon is reduced from 40~60μm to 10~30μm after modification. XRD patterns show that no new phase forms after Nd modification. The results of mechanical properties tests show that whole properties of modified samples are significantly improved. When Nd addition is 0.3%, tensile strength of the alloy reaches its maximum. Tensile strength is increased about 35.8% from 120 MPa to 163 MPa. Elongation was increased about 175% from 0.8% to 2.2%. The improvement of mechanical properties should attribute to fine primary after modification.
Authors: Yan Zhu, Wen Yong Jiang, Er Jun Guo, Ji Li, Kai Feng Wang
Abstract: Due to its good wear resistance, Al-20Si is widely used as piston. But coarse primary silicon greatly undermines the mechanical properties of Al-Si alloy. The primary silicon could be refined in pulse magnetic field with suitable magnetic flux density and magnetic field frequency. In this work, the microstructure of Al-20Si alloy with and without pulse magnetic field treatments was observed, and the influence mechanism of weak pulse magnetic on the microstructure of the alloy was investigated. The results showed that the grain size of primary silicon fluctuated with increasing magnetic flux density at 1Hz. The smallest grain size of primary silicon is obtained at 94mT. The grain size of the primary silicon decreased with increasing magnetic field frequency under the magnetic flux density of 94mT.
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