A new multi-zone model for porosity distribution in Al-Si alloy castings

Tiedje, Niels Skat, Taylor, John A. and Easton, Mark A. (2013) A new multi-zone model for porosity distribution in Al-Si alloy castings. Acta Materialia, 61 8: 3037-3049. doi:10.1016/j.actamat.2013.01.064

Author Tiedje, Niels Skat
Taylor, John A.
Easton, Mark A.
Title A new multi-zone model for porosity distribution in Al-Si alloy castings
Journal name Acta Materialia   Check publisher's open access policy
ISSN 1359-6454
Publication date 2013-05-01
Year available 2013
Sub-type Article (original research)
DOI 10.1016/j.actamat.2013.01.064
Volume 61
Issue 8
Start page 3037
End page 3049
Total pages 13
Place of publication Kidlington, Oxford, United Kingdom
Publisher Pergamon
Language eng
Abstract A new multi-zone model is proposed that explains how porosity forms in various regions of a casting under different conditions and leads to distinct zonal differences in pore shape, size and distribution. This model was developed by considering the effect of cooling rate on solidification and distribution of porosity in Al–Si alloys cast as plates in moulds made with silica, ilmenite or zirconia sand cores or steel chills facing the major plate faces. The alloys cast were Al–7 wt.% Si and Al–12.5 wt.% Si in unmodified and modified forms, the latter with either Na or Sr addition. It is found that, regardless of cooling condition, Si content and modification treatment, the microstructure can be divided into three zones of varying size (across the casting thickness) that are determined by the local cooling conditions and the nucleation and growth mode of the Al–Si eutectic. The zones are: (1) an outer shell-like zone where directional columnar dendritic grains and a fine-celled, coherent eutectic form a low-porosity shell at the casting surface; (2) a transitional zone where equiaxed, eutectic cells grow between columnar dendritic grains and irregular pores become trapped in the mush; and finally (3) a central zone where the thermal gradient is low and equiaxed dendritic grains and eutectic cells grow at the centre of the casting and larger, rounded pores tend to form. The paper discusses how Si content, modification type and cooling conditions influence the location and size (i.e. depth) of each of these zones and how the distribution of porosity is thus affected.
Keyword Al-Si alloys
Eutectic solidification
Heat flow and solidification
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mechanical & Mining Engineering Publications
Official 2014 Collection
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Citation counts: TR Web of Science Citation Count  Cited 10 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 15 times in Scopus Article | Citations
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