Papers by Keyword: Solidification

Abstract: Solidification behavior and phase relation of LaFe13-xSix alloys was investigated using arc melting. Phase formation and structure in arc melted LaFe13-xSix alloys has been investigated by means of power X-ray diffraction analysis and scanning electron microscopy. The results have shown that La(Fe,Si)13 (1:13) phase is a peritectic phase and the solidification behavior and phase relations of LaFe13-xSix alloys are different with Si contents. Under arc melting condition, composition with low Si contents (x=0.5 to 1.5) consist mainly of α-(Fe,Si) phase the same as induction melting. Composition with high Si contents (x=2.0 to 3.0) consists mainly of 1:13 phase. The results were discussed with respect to the effect of cooling rate.

Abstract: The consolidation and conservation of earthen sites is one of the difficult problems at home and abroad. Tianluoshan relic sites is a typical earthen sites located at humid circumstances. For public exhibitions and research purposes, a few chemical grouts were recommended for solidification and conservation of the excavated historical heritage sites. In this paper, the potential application of methyl acrylic acid resin for strengthening Tianluoshan relic soils were evaluated by a series of unconfined compression tests considering the influence of curing condition, curing time, and water content. The results showed that methyl acrylic acid resin can effectively improve the strength of Tianluoshan relic soils.

Abstract: A soil stabilizer was prepared by mixing saline soil, slag, desulfurization gypsum and clinker. The compressive strengths of samples is up to 6.11MPa when the mixing amount of slag, desulfurization gypsum and clinker at 14% after 7 days curing. Results show that the stabilizer can meet the sub-base engineering applications, is an ideal stabilizer.

Abstract: Fire scene investigation on fire caused by the wall socket,extracted the copper bead and aluminum wire material evidence,observe and analysis,include the macro analysis and metallographic analysis, and then confirmed the reason.Through the identification of the extracted fire material evidence,macro features are all electric heated,the metallographic analysis to determine the nature of the melted marks respectively for primary short circuit melted marks and over load melted marks and short circuit spatter melted mark. These three kinds of trace is in line when the electrical fault occurred formed, and a primary short circuit melted marks provides the most direct strong scientific basis for the cognizance of the fire,and determined the fires is caused by the faulted wall socket.

Abstract: Twin-roll casting is an efficient and economical process to fabricate metal sheets since it combines solidification and rolling in one process. However, this process requires a careful control because several phenomena, such as heat transfer, solidification, fluid flow and solid deformation, occur simultaneously. In the present study, a rigid-thermo-viscoplastic finite-element analysis was utilized to understand these complex phenomena occurring in a vertical twin-roll casting of an aluminum alloy. As a result several interesting findings were obtained including the development of two symmetrically identical vortexes at the roll entrance.

Abstract: The overall distribution of mechanical properties of A357 aluminum alloy connection beam casting after solidification and T6 heat treatment was researched in this paper, through the mechanics performance test, metallographic microstructure observation, SEM and EDS scanning analysis of the fracture surface, the ensemble mechanical properties of connection beam casting was characterized. The results show that owing to the low cooling rate nearby the arc thick-walled department and the trasition region between the thick and thin-walled of the connection beam casting, leading to the morphology of the crystalline grains and silicon particles in this vicinity are thick. Some casting defects such as oxide inclusions located in the lateral stud district were caused by the strong erosion of high temperature melting liquid during the pouring process, resulting in the mechanical properties decreased significantly, casting defects were not eliminated in the T6 heat treatment process. Due to both the high cooling rate and the smooth pouring process among the thin-wall, forward stud and square box region of A357 aluminum connection beam casting, after the solid solution and limitation strengthening of T6 heat treatment, resulting in the overall mechanical properties were higher than other areas. The tensile strength has reached 360.96MPa, also with the yield strength and elongation respectively attained 297.95MPa and 8.82 %.

Abstract: In the present study a hypomonotectic Al-0.9wt%Pb alloy was directionally solidified under transient heat flow conditions and the microstructure evolution was analyzed. The solidification thermal parameters such as the growth rate, the cooling rate and the temperature gradient were experimentally determined by cooling curves recorded by thermocouples positioned along the casting length. The monotectic structure was characterized by metallography and a microstructural transition was observed. From the casting cooled surface up to a certain position in the casting the microstructure was characterized by well-distributed Pb-rich droplets in the aluminum-rich matrix, followed by a mixture of fibers and strings of pearls from this point to the top of the casting. The interphase spacing (λ) and the diameter of Pb-rich particles were also measured along the casting length and experimental growth laws relating these microstructural features to the experimental thermal parameters are proposed.

Abstract: A phase-field model is proposed for the simulation of microstructure and solute concentration during the solidification of Fe-C-P-Mn quaternary alloys. In this paper, a study is presented to analyze both the effects of partition coefficient and solute diffusivity on the microstructural evolution during solidification simulation. Partition coefficient and diffusivity are very important from a practical standpoint, because both parameters exert a strong influence on the dendrite morphology. Additionally, the proposed model is applied for quaternary alloys to the analysis of the time-dependent solidified fraction. Simulations permit to conclude that the solidified fraction is proportional to the square root of time, as expected for any diffusion-controlled growth process. Phase-field simulations on non-isothermal dendrite growth are also examined. Two-dimensional simulation results exhibit different dendrites in multicomponent alloys for different solute concentrations. Changes in the carbon concentration seem to affect the dendrite morphology, due to its higher concentration and its lower equilibrium partition coefficient. Changes in the phosphorus concentration affect the dendrite morphology and the interface velocity, when its content is increased from 10^-3mol%P. Higher manganese content slows down the solidification kinetic, while the dendrite morphology remains unchanged.

Abstract: Solidification of ternary Al-Cu-Si alloys begins with the development of a complex dendritic network typified by primary (λ₁) and secondary (λ₂) dendrite arm spacings which depend on the chemical composition of the alloy and on the casting thermal parameters such as the growth rate and the cooling rate. These thermal parameters control the scale of dendritic arms, the size and distribution of porosity and intermetallic particles in the casting. In this paper, λ₁ and λ₂ were correlated with experimental thermal parameters i.e., the tip growth rate and the tip cooling rate. The porosity profile along the casting length has also been experimentally determined. The volumetric fraction of pores increase with the increase in alloying Si and with the increase in Fe concentration at the regions close to the casting cooled surface.

Abstract: The effects of chemical composition and cooling rate on the delta ferrite formation in austenitic stainless steels have been investigated. Ferrite fractions measured by a magnetic method were in the range of 0 to 12% and were compared with those calculated by empirical formulas available in the literature. The delta ferrite formation (amount and distribution) was strongly affected by the steel chemical composition, but less affected by the cooling rate. Among several formulas used to calculate the amount of delta ferrite, the best agreement was obtained with those proposed independently by Schneider and Schoefer, the latter being recommended in the ASTM 800 standard.