Papers by Keyword: Refinement

Abstract: s: The semi-solid slurry of Al-25%Si hypereutectic aluminum alloy was prepared through a copper serpentine pouring channel, the effect of pouring temperature and numbers of channel bend on the slurry microstructure was investigated. The results show that the primary silicon grains in Al-25%Si hypereutectic alloy solidified at a traditional condition are very large and the average silicon grain size is about 65.3μm, however, when the liquid Al-25%Si alloy is poured through a copper serpentine pouring channel, the primary silicon grains are fined obviously. If the channel has three bends and the pouring temperature is 747°C,the average silicon grain size in the slurry is about 33.7μm. If the channel has four bends and the pouring temperature is 747°C, the average silicon grain size in the slurry is about 30.9μm. If the channel has seven bends and the pouring temperature is 747°C, the average silicon grain size in the slurry is about 28.6μm. The analysis shows that the chilling effect of the inner channel wall precipitates primary silicon nuclei, and so the primary silicon grains of Al-25%Si alloy are fined greatly. Meanwhile, the subsequent washing of the alloy melt also promotes the separation of primary silicon grains from the inner wall and the primary silicon grains are further fined. The above research work demonstrates eventually that the copper serpentine pouring channel process is a good method for fining the primary silicon grains in hypereutectic Al-25%Si alloy rather than using chemical fining agent phosphorus as in traditional process.

Abstract: The objective of this paper aims at modeling and analysis of communication properties of an E-commerce protocol with the Event-B language. NetBill protocol is developed for selling and buying of information and goods through the Internet. In this approach, we have used Event-B as proof-based development method which integrates proof techniques for writing specifications and building the model systematically using refinement, the key point is to start with a very abstract model of the system under development. Step by step details are added to this first model by building a series of more concrete ones. This strategy eases the proof of the correctness of requirements because only a small number of proof obligations are generated at each step. The aims are constructing a model with a clear and accurate formulation of the communication protocol properties and discharge of all proof obligations. The outcome of this procedure was that we achieved a very high degree of automatic proof. We reached a good degree of automatic proof. All interactive proofs involved a small number of steps and were straightforward to reach.

Abstract: Blank dimensions and outlines can be obtained in one-step inverse analysis. Applying more accurate mesh will achieve more precise outlines while usually lead to the increase of computation time. To ensure operation efficiency, this paper proposes a new blank outline refinement algorithm based on one-step inverse analysis. Firstly, the initial configuration is obtained from the final configuration by one-step inverse analysis. Secondly, all outline nodes is projected to the nearest element in the final configuration. Thirdly, according to the position of projected nodes in the element, the coordinate of outline nodes in the initial configuration is achieved through mapping. Finally the number of outline nodes is increased in rounded corners, the coordinate of added nodes are calculated through interpolation. At last all outlines corresponding to characteristic lines of part surface are acquired. Using A-pillar as an example, outlines are calculated by the refinement algorithm and commercial software. It proves that under the same mesh quality, outlines obtained by refinement algorithm become more accurate and smooth, especially in rounded corner. The results can contribute to judge the rationality of blank shape and improve the final part forming property. This algorithm refines the accuracy of outlines and ensures the efficiency of one-step inverse analysis.

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: Effect of cooling rate on modification and refinement of 4032 aluminum alloy has been investigated at cooling rates of 0.7~4.5 K/s. Sr is used to modify eutectic silicon and B is used to refine primary α-Al grains. Modification level of eutectic silicon and refining results of primary α-Al are characterized quantitatively by L_p based on the perimeter of eutectic silicon particles and the maximum grain length D, respectively. As the cooling rate decreases, the needle-like eutectic silicon particles increases and the modification level reduces with a constant Sr content. Influenced by alloying elements such as Mg, Cu and Ni, the modification level is very low at the lowest cooling rate of 0.7 K/s, but properly increasing Sr content in the melt can improve the modification. At the cooling rates of 0.7~4.5 K/s, the element B can transform coarse columnar dendritic α-Al grains to equiaxed ones, and controlling the ratio of Sr and B is a valid technique to avoid mutual poisoning. On the conditions of present experiments, the Sr content of 350 ppm and Sr:B ratio of about 1.1 are rational to modify eutectic silicon and refine primary α-Al grains simultaneously.

Abstract: The exploration of efficient preparation methods of VO₂(M) powders, especially the controls of particle sizes, is a challenge. In this article VO₂(M) powders were prepared by a liquid phase precipitation and post annealing method. The structure and morphology of the VO₂(M) powders were characterized by XRD and SEM. The effects of annealing temperature and the amounts of additive SiO₂ aerogels on the particle size controlling were studied .The thermal phase transition properties were characterized by DSC analysis. The results reveal that the transformation of crystal phases from V₆O₁₃ to VO₂(M) takes place in the annealing process and the additive of SiO₂ aerogels can control the particle size and promote the particle size to be smaller effectively.

Abstract: Owing to its beneficial material properties, Al-Mg₂Si in-situ composite has recently received wide attention and application in the manufacture of automotive and aerospace components. Melt treatment of the in-situ composite with the addition of Ce has resulted in a change in the primary and eutectic Mg₂Si phases to refined morphology, which would be expected to improve the mechanical properties of the composite. Characteristic parameters of Mg₂Si particles have been investigated via thermal and microstructural analysis. This has revealed that the addition of 0.8wt.% Ce produced optimum refinement effects on Mg₂Si_P because the coarse structure has been changed to a polygonal shape and reduced in size. Similarly, the flake-like morphology of Mg₂Si_E has been transformed into a rod-like or fibre form in addition to reduction of the eutectic cell area. The result also showed an increase in nucleation temperature T_N of Mg₂Si_P while depressed for Mg₂Si_E, which also corresponds to the refinement morphology effect.

Abstract: Grain refinement has a strong influence on material strength. Therefore, the automatic evaluation method of the grain refinement level is useful. In order to develop a grain size analysis system, we applied the homology theory to prior austenite grain analysis. We prepared repeatedly quenched high-carbon high-chromium steel samples (JIS-SUJ2) and evaluated their microstructures in order to investigate the relation between the Betti numbers (b₀ and b₁) and prior austenite grains. We found that the Betti number (b₁) is strongly correlated to the number of grains.

Abstract: To increase the industrial applicability of hypereutectic Al-Si alloys, various methods have been used to refine primary silicon. The addition and refinement effects of phosphorus (P), rare earth metals (RE) on primary Si have been studied widely, But they have been testified be with some disadvantages, that is, the pollution to the environment of P and the high cost of RE, etc. Now, a new refiner - ZnS and the corresponding processing technology were researched. Microstructures of hypereutectic Al-Si alloy (Si wt. 24%) with fine primary Si were successfully obtained. And the primary Si can be refined from more than 80μm to 20μm. And the distribution of primary silicon is getting more uniform.

Abstract: In order to evaluate the effect of heating pattern on the grain structure refinement of bearing steel (JIS, SUJ2), samples were quenched once, twice and three times. After quenching, the samples were polished and etched with Van Gieson solution. Based on our former investigations using Homology analysis, the Betti numbers of the prior austenite grains were observed. It was concluded that the Betti numbers of the grains were strongly correlated to the refined structure.