Papers by Keyword: Hypereutectic Al-Si Alloy

Abstract: P-doped γ-Al₂O₃ was found to be a potent substrate to nucleate primary silicon whilst good modification of the eutectic matrix is retained during solidification of hypereutectic Al-Si alloys. On using P-doped γ-Al₂O₃ could be a perfect and clean source of P without additional impurities. The optical micrographs show that the morphologies of primary silicon crystals in solidification of Al-18Si alloy are changed from irregular coarse morphologies to fine regular particles. The average particle size of primary Si decreased from 52 μm to 25 μm and 22 μm in adding P-doped α-Al₂O₃ and P-doped γ-Al₂O₃ respectively. It was clear that P-doped γ-Al₂O₃ led to good refinement of primary Si and the modification effect on eutectic Si was retained in solidification of commercial purity Al-18Si alloy. Adding P-doped γ-Al₂O₃ give a good primary Si refinement to Al-18Si alloy if compared with the addition of P and using finer P doped γ-Al₂O₃ powder give narrower particle size range similar to that of adding P.

Abstract: The effect of phosphorus on primary silicon, phosphorus and mischmetal (Ce-50La) modification on primary and eutectic silicon and cooling rate on microstructure of Al-25%Si are investigated. The results show that, with the addition of phosphorus, the size of primary silicon decreases from 93.6μm to 24.75μm. The morphology of primary silicon changes from irregular to polygonal. When Al-25%Si is modified by phosphorus and mischmetal, primary and eutectic silicon all change effectively. Addition of mischmetal on the basis of phosphorus modification have no influence to primary silicon, but it can make morphology of eutectic silicon change from lamellar to short rod-like when the content of mischmetal reaches 0.5%. The cooling rate curves show the change of temperature in different height of wedge-shaped mould. When cooling rate increases, microstructure of Al-25%Si refines, the size of primary silicon decrease to 22.7μm. The results obtained from mechanical testing demonstrate that the addition of mischmetal and increasing of cooling rate increase hardness value of Al-25%Si alloy.

Abstract: In the present paper, based on Bi-containing hypereutectic Al-20%Si alloy, a rotating magnetic field was used, the microstructures of the alloy have been observed and analyzed by optical microscope and scanning electronic microscope, and its wear-resisting property was measured. The influence mechanism of rotating magnetic field on the microstructures and properties of the alloy has been discussed. Research results show that exerting a rotating magnetic field in the hypereutectic Al-20%Si alloy drastically decreases the amount of primary Si phase, only some tiny bulk Si exist and the amount of needle eutectic Si increase. The dendrite-like primary α-Al appears at the same time. With the increase of stirring rate of rotating magnetic field, the change way of eutectic Si shape is coarse needle→tiny needle→coarse needle; the rotating magnetic field can change the nonuniform distribution of Bi induced by Bi local decentralization. With the increase of stirring rate of rotating magnetic field, the change way of Bi shape in upper part microstructures of the alloy is large bulk→short rodlike→big globular→small globular, Bi local decentralization is changed into uniform distribution; In addition, exerting a rotating magnetic field in the hypereutectic Al-20%Si alloy can increase wear-resisting property of the alloy.

Abstract: In the dissertation the influence of overheating of around 250^oC above T_liq on the material reliability of AlSi17Cu5 cast alloy has been shown. On the basis of static tensile test, the following had been determined: HB hardness, tensile strength and yield strength for four, chosen technological variants. The results were the base to verify the thesis of compliance between tested feature arrangement and normal arrangement, and on this ground also material reliability determined with Weibull’s statistic arrangement had been defined. This parameter grasp the interdependence between lasting probability and chosen material property of the alloy.

Abstract: In the dissertation the influence of overheating of around 250°C above T_liq and modification with phosphorus (CuP10 master alloy) on the microstructure of AlSi17Cu5 cast alloy has been shown. Substantial overheating above T_liq temperature of the alloy, causes complete dissolving of the β (Si) phase. In the liquid alloy, multiple areas are being created of different dissolved silicon content, where, as in the result of the overheating, the homogeneous nucleuses are being partially created. After modification with phosphorus, in liquid alloy, additional heterogenic nucleuses (AlP) of primary silicon crystals are being created. In the close neighborhood of these micro-areas, places depleted of silicon appears, where pre-eutectic α (Al, Me) dendrites crystallize.

Abstract: In this paper, the wear property of a rheo-squeeze casting Al-22Si-2Fe-1.4Mn alloy tube was investigated. The semi-solid slurry of Al-22Si-2Fe-1.4Mn alloy was prepared using segmented cooling plates. The results showed that the volume fraction and equivalent diameter of the hard particles (primary silicon and blocky Fe-rich phases) increased gradually from the outside to the inside of the tube wall. The microstructures of the tube were examined with an optical microscope, scanning electron microscope, X-ray diffraction. The micro-hardness of hard particles and the macro-hardness from the outside to the inside of the wall were tested, respectively. Wear resistance tests of the outside and the inside of the wall showed wear resistance, which depends on the distribution and the volume fraction of the hard particles, increased gradually from the outside to the inside of the tube wall, changed in gradient and agreeing with the distribution law of macro-hardness.

Abstract: Hypereutectic Al-Si alloys have low thermal expansion coefficients, excellent wear resistance, and high hardness. To replace cast iron with hypereutectic Al-Si alloys, the hypereutectic Al-Si alloys must still have the originally desired mechanical properties. The addition of Fe and Mn to the hypereutectic Al-Si alloys can form Fe-rich phases, which can improve thermal stability. In this paper, the effect of manganese (0 %, 0.99 %, and 1.36 %) on the Fe-rich phases of hypereutectic Al-22Si-2Fe (% w/w) alloys was studied. The results showed that primary Si particles (PSPs), needle-like Fe phases, a coarser fishbone-shaped α-Al₁₅(Fe, Mn)₃Si₂ phases, and eutectic Si could be refined by cooling slope. With such a CS process, the intermetallic compounds in the alloys with different Mn/Fe ratios were examined with an optical microscope, scanning electron microscope, and X-ray diffraction. Moreover, the blocky α-Al₁₅(Fe, Mn)₃Si₂ phases were analyzed by transmission electron microscopy. Through the analysis of the SADP, the lattice structures of α-Al₁₅(Fe, Mn)₃Si₂ phases were identified with tetragonal structure and body centre cubic.

Abstract: The Fe-rich Al-Si alloys have the potential to be used to make wear-resistant parts. However, there has been few work devoted to study the wear behavior of the hypereutectic Al-Si alloys with about 2% Fe (mass %). In this work, the semi-solid slurry of the alloy was prepared by an ultrasonic vibration (USV) process. The effect of Fe content on dry sliding wear properties of the alloys rheo-casted after USV treatment was investigated. The wear tests were carried out using a pin-on-disc wear tester at four different loads of 50N, 100N, 150N and 200N at a constant sliding speed of 0.75m/s. The results show that the wear rate of USV treated alloy increases almost linearly as the applied load increases from 50 N to 200N. The alloys made with semi-solid process exhibited improved wear resistance at the entire applied load range in comparison to the conventional casting alloys. At the applied load of 50N, oxidative wear is the dominant mechanism for the alloys with USV treatment. At 200N, a combination of delamination and oxidation wear is the main wear mechanism. The wear resistance of Al-17Si alloys containing 2% to 3% Fe is closely related to the morphology, size and volume fraction of Fe-bearing compounds, which can be changed by USV semi-solid process.

Abstract: In this paper, the effects of process parameters on the absorption rate of P for hypereutectic Al-Si alloy (A390) which modified with Cu-14%P master alloy were systematically studied. And the mechanism that the process parameters play a role in effecting on the absorption rate of P was deeply investigated. The results indicated that the absorption rate of P increased with the increase of modified time and temperature, and decreased with the increase of the amount of added P. Under the same process condition, P added in form of Cu-14%P particles can cause to obtain the higher absorption rate of P than that of Cu-14%P powders. According to the experimental results, an equation on changes of the absorption rate of P was proposed, and the results show that good agreement is obtained between calculated and experimental values. The process parameters played a role in effecting on the absorption rate of P mainly through affecting the reaction rate of forming AlP particles in the melt, as well as the degree of reaction reached.

Abstract: The effect of ultrasonic melt treatment (UST) on the microstructure of hypereutectic Al-17 wt.% Si alloys was investigated. UST applied to a melt at a temperature range of 750 - 800 °C refines the primary Si dramatically but has little influence on the grain size of primary Al. The solidification behaviour was characterised by thermal analysis and a mechanism responsible for the primary Si refinement was suggested. Whilst UST has no effect on the grain refinement, a significant increase in the matrix hardness as well as the tensile strength in the as cast condition is possibly associated with solid solution hardening. Detailed microstructure analysis was carried out and characteristics of the intermetallic formation in the Al-17 wt.% Si alloys were further discussed in the view point of Cu solubility in the Al matrix, which is considered to increase with UST.