Grain refinement of an aluminum alloy by introducing gas bubbles during solidification

Wannasin, Jessada; Martinez, R. A.; Flemings, M. C.

doi:10.1016/j.scriptamat.2006.04.003

Cited by 110 publications

(56 citation statements)

References 5 publications

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“…This indicates that gas bubble stirring has an important influence on the formation of spheroidal primary particles. This is consistent with the work of WANNASIN et al [16]. Semi-solid slurry with well spheroidal primary particles can be obtained with suitable processing parameters.…”

Section: Methodssupporting

confidence: 93%

“…This process used gas bubbles as the medium to stir the melt during the initial stage of solidification. A rotating tube-like graphite agitator was applied, which is different from the static graphite diffuser used by WANNASIN et al [16]. Three different solidification conditions were obtained by pouring the semi-solid slurry into an iron mold, a copper mold cooled in water, and directly quenching in water.…”

Section: Introductionmentioning

confidence: 99%

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Microstructure evolution of Al-Si semi-solid slurry by gas bubble stirring method

Zhang

Dong

et al. 2011

J. Cent. South Univ. Technol.

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A novel technique of introducing gas bubble stirring during solidification was studied to prepare Al-Si semi-solid slurry. The microstructure evolution of the slurry during slow cooling process after stirring was investigated. The effects of the solidification rate on the microstructure of the semi-solid slurry were investigated under three different solidification conditions. The results show that fine non-dendritic slurry can be obtained using the gas bubble stirring method. Ripening and coarsening of primary Al grains are observed during the slow cooling process, and at last coarsened eutectic Si appears. Primary Al grains with different sizes and eutectic Si are obtained, corresponding to three different solidification rates.

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Section: Methodssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Microstructure evolution of Al-Si semi-solid slurry by gas bubble stirring method

Zhang

Dong

et al. 2011

J. Cent. South Univ. Technol.

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“…Besides the partial re-melting of sprayformed materials [3], generally speaking, the methods of making semi-solid slurry containing spheroidal Al grains can be mainly classified into two categories. One is agitation either mechanically or electromagnetically [1] including SEED process [4] and bubbling process [5]. The other one includes strain-induced melt activation (SIMA) [6] and recrystallization and partial melting (RAP) route [7], which can be used to get spheroidal grains via partially re-melting of previously deformed (rolling, extrusion, etc.)…”

Section: Semi-solid Processesmentioning

confidence: 99%

Analysis of microstructure evolution and precise solid fraction evaluation of A356 aluminum alloy during partial re-melting by a color etching method

2012

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Spheroidization of Al grains is required for the production of semi-solid slurry either by a partial solidification route or partial re-melting route. In this research, A356 aluminum alloy was deformed and partially re-melted to semi-solid state. A segregation sensitive reagent (Weck's reagent) was used to reveal the inner microstructure of Al grains for the better understanding of the microstructure evolution during partial re-melting. Optical microstructure observation showed that the previously compressed Al dendrites were actually ''fractured'' during heat treatment and such ''fractured'' dendrites contributed to the refinement and spheroidization of Al grains. Further study of this phenomenon indicates that the ''fractures'' are actually migrating high-angle grain boundaries, which was related to the recrystallization that occurred during heat treatment. Moreover, the growth layer of Al grains formed during water quenching is clearly visualized after being etched by Weck's reagent. Consequently, precise evaluation of solid fractions through image analysis was realized by excluding growth layer when measuring the area of solid phase.

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“…Several rheocasting techniques have been invented for preparing semi-solid metal slurries for casting. Gas Induced Semi-Solid (GISS) is a new semi-solid slurry preparation technique recently developed [1]. In the GISS technique, fine inert gas bubbles are injected through a graphite diffuser into the molten alloy, causing a vigorous agitation and a rapid heat extraction from the molten metal, at early stage of solidification the semisolid structure is formed.…”

Section: Extended Abstractmentioning

confidence: 99%

Forming Gears from ZA-27 Zinc Alloy Using Semi-Solid Slurry Squeeze Casting Process

Plookphol¹,

Janudom²,

Vongcharoenpon³

2017

World Congress on Mechanical, Chemical, and Material Engineering

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Extended AbstractSemi-solid metal processing has been developed for years. The semi-solid metal processing can be classified into two types, thixoforming and rheocasting. In recent years, the rheocasting process gains more attention from the industries since it has a lower capital cost and materials cost. Several rheocasting techniques have been invented for preparing semi-solid metal slurries for casting. Gas Induced Semi-Solid (GISS) is a new semi-solid slurry preparation technique recently developed [1]. In the GISS technique, fine inert gas bubbles are injected through a graphite diffuser into the molten alloy, causing a vigorous agitation and a rapid heat extraction from the molten metal, at early stage of solidification the semisolid structure is formed. The GISS technique can be used with many alloys to create semi-solid slurries, such as aluminum alloys, zinc alloys and tin alloys, and it can be used with conventional casting processes, such as die casting, squeeze casting and gravity casting [2,3]. The purpose of present study is to evaluate a possibility of using the GISS technique and squeeze casting process for producing gears from a high strength Zn-Al alloy. Commercial ZA-27 zinc alloy with nominal chemical compositions of 27-28 wt.% Al, 2.0-2.5 wt.% Cu and the remaining Zn, was used in this study. Effects of rheocasting time and preheating die temperature on the completeness of gear specimens were evaluated. Nitrogen gas was used and the gas bubbles were introduced into molten ZA-27 alloy through a porous graphite diffuser at temperature 510 C for 10 and 15 s. Two preheating die temperatures, 270 and 300 C were used for preheating gear die set before squeeze casting was commenced. Semi-solid alloy slurry was squeezed in the die with a hydraulic compression pressure of 100 MPa for 30 s. Microstructural analysis and hardness testing were performed on the as-cast gear specimens. It was found that using rheocasting time both 10 and 15 s and preheating die temperature 270 C cannot produce complete gears. Some gear teeth were not completely formed since the cooling rate was too fast and solidification was completed before the alloy slurry could fill up the gear teeth die space. Complete gear specimens were successfully achieved when using rheocasting time 15 s and preheating die temperature 300 C. Average hardness of as-cast gear teeth and gear body was 68.3±2.7 and 69.6±1.1 HRB, respectively. Microstructures of gear teeth and gear body consisted of globular Al-rich α phase, surrounded by β, η and ε phases. Segregation with dendritic structure was formed on the rim of some gear teeth, with thickness of 0.5-1 mm. From the present study it can be concluded that it is possible to form ZA-27 zinc alloy gears using the GISS slurry squeeze casting process by appropriate control process parameters: the rheocasting temperature, the rheocasting time, and the preheating die temperature. References[1] J. Wannasin, R. Martinez and M. Flemings, "Grain refinement of an aluminium alloy by introducing gas bubbles d...

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Grain refinement of an aluminum alloy by introducing gas bubbles during solidification

Cited by 110 publications

References 5 publications

Microstructure evolution of Al-Si semi-solid slurry by gas bubble stirring method

Microstructure evolution of Al-Si semi-solid slurry by gas bubble stirring method

Analysis of microstructure evolution and precise solid fraction evaluation of A356 aluminum alloy during partial re-melting by a color etching method

Forming Gears from ZA-27 Zinc Alloy Using Semi-Solid Slurry Squeeze Casting Process

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