Na Wang Zhimin Zhou
材料科学技术（英文）
The semi-solid billet of 6061 aluminum alloy was prepared by the near-liquidus semi-continuous casting (LSC) with rosette or near-spheroide grains. The pre-deformation processing was applied before partial remelting to further improve the microstructure and properties of the semi-solid alloy. The effects of different processing parameters, such as holding temperature and holding time, on the semisolid microstructures during partial remelting have been investigated. It was found that the optimal partial remelting parameters should be 630°C and 10{15 min for 6061 alloy cold rolled with 60% reduction in height of pre-deformation. The coarsening rates were anasysed by Lifshitz-Slyozov-Wagner (LSW) theory. The pre-deformed 6061 alloy exhibits lower coarsening rate constants than that of the as-cast one, and also lower than other alloys processed by different method found in previous literature. It is because the coarsening rate is associated with the initial microstructure and composition of the alloy. The secondary phases in the alloy inhibit the migration of the liquid film grain boundaries. The microstructure obtained by using the combination of near-liquidus semicontinuous casting and pre-deformation treatment is better than that without pre-deformation processing, which demonstrates that the used method is promising for fabricating high quality semi-solid alloys.
关键词:
Semi-solid forming
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Near-liquidus semi-continuous casting
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6061 alloy
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Pre-deformation
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Partial remelting
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Coarsening
Tijun CHEN
,
Yuan HAO
,
Jun SUN
材料科学技术（英文）
The investigations were performed into the formation processes of liquid pools entrapped within solid grains of three ZA27 alloys, produced respectively by either grain refinement, or traditional permanent casting or mechanical stirring, during partial remelting at semisolid temperature of 460°C. The results show that the rapid coalescence of primary grains due to merging of secondary arms during the initial stage of partial remelting is the main cause for the formation of the entrapped liquid pools. This coalescence resulted in that a high quality of eutectics, especially the h phase, was entrapped within the grains, and then remelted to form liquid pools during the subsequent heating. In addition, the growth of the h phase decomposed from the primary a' phase and b phase and the subsequent remelting is another cause for the refined and permanent mould casting alloys. Furthermore, the agglomeration of the solid grains also resulted in the entrapment of liquid in the interior of grains.
关键词:
Thixoforming
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null
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null
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