Segregation band formation in Al-Si die castings

Banded defects are often found in high-pressure die castings. These bands can contain segregation, porosity, and/or tears, and changing casting conditions and alloy are known to change the position and make-up of the bands. Due to the complex, dynamic nature of the high-pressure die-casting (HPDC) p...

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Bibliographic Details
Published in:Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2004-09, Vol.35 (9), p.2881-2891
Main Authors: GOURLAY, Christopher M, LAUKLI, Hans I, DAHLE, Arne K
Format: Article
Language:English
Subjects:
Aluminum alloys
Applied sciences
Defects
Die casting
Exact sciences and technology
Materials science
Metals. Metallurgy
Microstructure
Shear stress
Solidification
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Summary:Banded defects are often found in high-pressure die castings. These bands can contain segregation, porosity, and/or tears, and changing casting conditions and alloy are known to change the position and make-up of the bands. Due to the complex, dynamic nature of the high-pressure die-casting (HPDC) process, it is very difficult to study the effect of individual parameters on band formation. In the work presented here, bands of segregation similar to those found in cold-chamber HPDC aluminum alloys were found in laboratory gravity die castings. Samples were cast with a range of fraction solids from 0 to 0.3 and the effect of die temperature and external solid fraction on segregation bands was investigated. The results are considered with reference to the rheological properties of the filling semisolid metal and a formation mechanism for bands is proposed by considering flow past a solidifying immobile wall layer. [PUBLICATION ABSTRACT]
ISSN:1073-5623
1543-1940
DOI:10.1007/s11661-004-0236-z