Segregation band formation in Al-Si die castings |
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Authors: | Christopher M. Gourlay Arne K. Dahle Hans I. Laukli |
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Affiliation: | (1) the CRC for Cast Metals Manufacturing, Division of Materials Engineering, The University of Queensland, 4072 Brisbane, QLD, Australia;(2) the Department of Materials Technology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway |
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Abstract: | 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. |
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