• Journal of Korea Foundry Society
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• v.11 no.3
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• pp.208-216
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• 1991

The solidification behavior of the squeeze cast composites of aluminum alloys reinforced with boron fiber($100{\mu}m$) and silicon carbide fibers($140{\mu}m$ and $15{\mu}m$) were investigated. Al-4.5wt%Cu and Al-l0wt%Mg were chosen for the matrix phase of the composites. In the squeeze cast specimen with high thermal difference between fiber and melt, the average secondary dendrite arm spacing(DAS) in reinforced alloy is smaller than that in unreinforced alloy. It was also observed that primary ${\alpha}$ and non-equilibrium eutectic, which seems to be penetrated and solidified at the final stage of the solidification of the matrix, are irregularly distributed around fibers. It is considered that cold fibers serve as heterogeneous nucleation site. While in the remelted and resolidified specimen without temperature difference, the DAS was not changed with reinforcement and microstructure reveals non-equilibrium eutectic with relatively uniform thickness around fibers. It might be evident the nucleation starts at interfiber region. Microsegregation decreases with the decrease in cooling rate and with reinforcement in the as-squeeze cast specimen. Al-10wt% Mg alloy shows less microsegregation than Al-4.5wt%Cu alloy.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.3
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• pp.426-434
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• 2000

This paper deals with a generalized similarity solution for the one-dimensional solidification of ternary or higher-order multicomponent alloys. The present approach not only retains the existing features of binary systems such as temperature- solute coupling, shrinkage-induced flow, solid-liquid property differences, and finite back diffusion, but also is capable of handling a multicomponent alloy without restrictions on the partition coefficient and microsegregation parameter. For an alloy of N-solute species, governing equations in the mushy region reduce to (N+2) nonlinear ordinary differential equations via similarity transformation, which are to be solved along with the closed-form solutions for the solid and liquid regions. A linearized correction scheme adopted in the solution procedure facilitates to determine the solidus and liquidus positions stably. The result for a sample ternary alloy agrees excellently with the numerical prediction as well as the reported similarity solution. Additional calculations are also presented to show the utility of this study. Finally, it is concluded that the present analysis includes the previous analytical approaches as subsets.

• Advances in materials Research
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• v.13 no.2
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• pp.141-151
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• 2024

The aim of this work was to determine the behavior of alloy elements and compounds formed during solidification in the manufacturing process of the CuAgZrCr alloy under an oxidizing environment. Bulk and surface analysis techniques, such as Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Raman and X-ray diffraction (XRD) were used to characterize the phases obtained in the solidification process. In order to focus the analysis on the on grain boundary interface, partial removal of the matrix phase by acid attack was performed. The compositional differences obtained by SEM-EDX, Raman and XPS on post-manufacturing materials allowed us to conclude that the composition of grain boundaries of the alloy is directly influenced by the oxidizing environment of alloy manufacturing.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3361-3370
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• 1996

Micro-Macro approach is conducted for the mixture solidification to handle the closely linked phenomena of microscopic solute redistribution and macroscopic solidification behavior. For this purpose, present work combines the efficiency of mixture theory for macro part and the capability of microscopic analysis of two-phase model for micro part. The micro part of present study is verified by comparison with experiment of Al-4.9 mass% Cu alloy. The effect of back diffusion on the macroscopic variables such as temperature and liquid concentration, is appreciable. The effect, however, is considerable on the mixture concentration and eutectic fraction which are indices of macro and micro segregation, respectively. According to the diffusion time, the behavior near the cooling wall where relatively rapid solidification permits short solutal diffusion time, approaches Scheil equation limit and inner part approaches lever rule limit.

• Metals and materials international
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• v.24 no.6
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• pp.1376-1385
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• 2018

Ultrasonic melt treatment (UST) was applied to an A390 hypereutectic Al-Si alloy in a temperature range of $750-800^{\circ}C$ and its influence on the solidification structure and the consequent increase in strength was investigated. UST at such a high temperature, which is about $100^{\circ}C$ above the liquidus temperature, had little effect on the grain refinement but enhanced the homogeneity of the microstructure with the uniform distribution of constituent phases (e.g. primary Si, ${\alpha}-Al$ and intermetallics) significantly refined. With the microstructural homogeneity, quantitative analysis confirmed that UST was found to suppress the formation of Cu-bearing phases, i.e., $Q-Al_5Cu_2Mg_8Si_6$, $Al_2Cu$ phases that form in the final stage of solidification while notably increasing the average Cu contents in the matrix from 1.29 to 2.06 wt%. A tensile test exhibits an increase in the yield strength of the as-cast alloy from 185 to 208 MPa, which is mainly associated with the solute increment within the matrix. The important role of UST in the microstructure evolution during solidification is discussed and the mechanism covering the microstructure-strengthening interrelationship of the ultrasonically treated A390 alloy is proposed.

• Journal of Korea Foundry Society
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• v.30 no.1
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• pp.34-45
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• 2010

The effects of alloy elements and cooling rate on the solidification path and the formation behavior of $\beta$ phase in Fe-containing Al-Si alloys were studied based on the thermodynamic analysis and the pertinent experiments. The thermodynamic calculation was systematically performed by using Thermo-Calc program. For the thermodynamic analysis in high alloy region of Al-Si-Fe ternary system, a thermodynamic database for Thermo-Calc was correctly updated and revised by the collected up-to-date references. For the thermodynamic-based prediction of various solidification paths in Fe-containing Al-Si system, liquidus projection of Al-Si-Fe ternary system, including isotherms, invariant, monovariant, bivariant reactions and equilibrium temperatures, was calculated and analyzed as functions of composition and temperature. The calculated results were compared to the experimental results using various casting specimens. In order to analyze various solidification sequences as functions of Si and Fe content, 4 representative alloy compositions, low Fe content in both low and high Si contents and high Fe content again in both low and high Si contents, were designed in this study. For better understanding of the influence of cooling rate on the formation behavior of $\beta$ phase, 4 alloys were solidified under furnace and rapidly cooled conditions. Cooling curves of solidified alloys were recorded by thermal analysis. Various important solidification events were evaluated using the first derivative-cooling curves. Microstructures of the casting samples were studied by the combined analysis of optical microscopy (OM) and scanning electron microscopy (SEM).

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.897-905
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• 2012

Directional solidification experiments were carried out in a hypoeutectic Al-11.3Si-3.5Cu system to investigate the microstructural evolution with the solidification rate. At a fixed temperature gradient, a dendritic microstructure was observed at a constant speed of more than $25{\mu}ms^{-1}$, a cellular interface developed at $5{\mu}ms^{-1}$ and the growth rate of $0.5{\mu}ms^{-1}$ led to the stability of the planar interface. The results revealed that primary silicon phases formed among cells, even though the studied Al-Si alloy system formed the composition within a hypoeutectic silicon composition. This suggests that the liquid concentration among cells during solidification reached a higher concentration, i.e., the eutectic concentration. It is, however, interesting that primary silicon phases did not form during a dendritic growth of more than $25{\mu}ms^{-1}$. These experimental observations are explained using the theoretical models on the interface temperatures.

• Korean Journal of Materials Research
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• v.14 no.2
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• pp.101-109
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• 2004

The influences of solidification rates and carbon contents on the formation of the $\delta$-ferrite were studied by directional solidification in modified 12%Cr-l %Mo steels. Directional solidification experimental results showed that solidification microstructure depended on solidification rate and carbon content and chromium equivalent. The length of the mushy zone increased and the dendrite arm spacings decreased as the solidification rate increased. The volume fraction of the 8-ferrite decreased with increasing the solidification rate and carbon content. The volume fraction of the ferrite showed much higher at low solidification rates with planar and cellular interfaces than that at high solidification rates with dendritic interface. It is expected that macro-segregation of C causes lower C content at the lower solidification fraction in the directionally solidified sample, where lower C results in higher volume fraction of the ferrite. In order to estimate solidification microstructure in modified 12Cr-l%Mo steels, various solidification conditions, such as solidification rate, cooling rate, segregation, alloy composition, should be considered.

• Journal of Welding and Joining
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• v.22 no.5
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• pp.65-72
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• 2004

The tendency and degree of hot cracking of high strength 5083, 6N01 and 7N01 Al alloy welds by using DCSP-GTAW through modified Varestraint test and autogenous butt welding were investigated. In hot cracking test, 6N01 alloy showed the highest susceptibility to hot cracking in the weld metal and HAZ. Cracking susceptibilities generally increased with increase of solidification temperature range of the base metal and bead penetration-to-width ratio of the weld metal. The cracks in welds of the alloys vertically formed to solid-liquid interface and propagated along with columnar grain boundaries. The fracture facets of cracks showed the typical morphology of solidification crack observed as dendritic structures. Especially, in 6N01 alloy, liquation cracks which were due to elements of Si, Fe and Mg also observed in HAZ near fusion boundary. In butt welding of different Al alloys, the bead crack was mainly occurred in the welds of 6N01, 7N01 and other Al alloys together with 6N01 or 7N01. In the butt welds of 7N01, it was found that the component of Cu had an effect on the higher susceptibility to the hot cracking.

• Journal of Korea Foundry Society
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• v.13 no.2
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• pp.155-162
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• 1993

This study has been focused on the influence of the metallic mold cooling effects on the solidification structures and the mechanical properties for Al-10%Si alloy castings by the variation of pouring temperatures, metallic mold temperatures and Cooling part of metallic mold. The dendrite arm spacing of Al-10%Si alloy was decreased with increasing cooling rate. In case of bottom cooling of metallic mold, DAS was appeared to be $20-22{\mu}m$ and in the middle cooling, it was increased to $36-40{\mu}m$. The DAS decreased proportionally $with(cooling\;rate)^{-3/2}$ at pouring temperatures $680^{\circ}C$ and $(cooling\;rate)^{-1/2}$ at pouring temperature $760^{\circ}C$, but it was proportionally increased to $(local\;solidification\;time)^{1/2-1/3}$ at pouring temperature $680^{\circ}C$ and $760^{\circ}C$. The maximum tensile strength of Al-10%Si alloy casting was obtained in case of bottom cooling of mold at pouring temperature $680^{\circ}C$ and metallic mold temperature $320^{\circ}C$.