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Powell, G. L. F.; Colligan, G. A.

doi:10.1007/bf02814979

Cited by 1 publication

(2 citation statements)

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“…[5] In strontium-modified alloys, the eutectic grains seem to range between 3-and 4-mm diameter, [2,5,9] while in sodiummodified alloys, equiaxed grains are either absent (or at least difficult to detect) [5,[7][8][9] or are in the range of 5 to 25 mm diameter. [3,14,15] In other research, micrographs were not provided, but it was commented that sodium and strontium additions resulted in a small number of large eutectic grains. [11] In summary, there is sufficient evidence to suggest that the eutectic grain size increases with impurity modification and this increase is larger for additions of sodium than for additions of strontium.…”

Section: Introductionmentioning

confidence: 99%

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Eutectic grains in unmodified and strontium-modified hypoeutectic aluminum-silicon alloys

McDonald

Dahle

Taylor

et al. 2004

Metall Mater Trans A

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Additions of strontium to hypoeutectic aluminum-silicon alloys modify the morphology of the eutectic silicon phase from a coarse platelike structure to a fine fibrous structure. Thermal analysis, interrupted solidification, and microstructural examination of sand castings in this work revealed that, in addition to a change in silicon morphology, modification with strontium also causes an increase in the size of eutectic grains. The eutectic grain size increases because fewer grains nucleate, possibly due to poisoning of the phosphorus-based nucleants, that are active in the unmodified alloy. A simple growth model is developed to estimate the interface velocity during solidification of a eutectic grain. The model confirms, independent of microstructural observations, that the addition of 100 ppm strontium increases the eutectic grain size by at least an order of magnitude compared with the equivalent unmodified alloy. The model predicts that the growth velocity varies significantly during eutectic growth. At low strontium levels, these variations may be sufficient to cause transitions between flake and fibrous silicon morphologies depending on the casting conditions. The model can be used to rationally interpret the eutectic grain structure and silicon morphology of fully solidified aluminum-silicon castings and, when coupled with reliable thermal data, can be used to estimate the eutectic grain size.

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Section: Introductionmentioning

confidence: 99%

“…Equiaxed eutectic grains do not appear to nucleate ahead of this interface in the bulk of the sample. [5][6][7]9,13] Despite this, equiaxed eutectic grain boundaries have been observed in fully solidified sodium-modified alloys of eutectic composition with [1] and without [14] additions of copper.…”

Section: Introductionmentioning

confidence: 99%