Abstract
Crystallographic orientation relationships between primary silicon and aluminum halo crystals in hyper-eutectic Al-Si alloys have been studied by micro-focus X-ray diffraction analysis.
The apparently random orientation relationships have been classified into simple relationships when the twinnings in silicon crystals are taken into consideration. These relationships are;
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oindentfor untreated alloys and,
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oindentfor sodium treated alloys.
The occurrence of relationships (1) for untreated alloys and (4) for sodium treated alloys are most frequent and it has been calculated that the relationships (2) and (3) are within 13.8° inclination from (1) and the relationships (5) and (6) are within 11.4° inclination from (4).
The crystallographic relationships between silicon and aluminum for untreated and sodium treated alloys, when represented by (1) and (4) respectively, can be matched by a 54.7° rotation around the [001] axis of aluminum crystals.
