The effect of iron and manganese on the formation of intermetallic compounds in aluminum–silicon alloys

The effect of iron and manganese concentration on the morphology of complex intermetallics has been studied in an Al–12.7 wt.% Si alloy containing 0.1 wt.% Cr with three levels of iron (0.4, 0.8, 1.2 wt.%), and five different levels of manganese ranging from 0.0 to 0.5 wt.%. The intermetallic compounds form at high iron contents or at high concentrations of manganese and chromium with low iron. Star-like intermetallics form when the segregation factor is greater than 1.30. Chromium (0.1 wt.%) with more than 0.2 wt.% manganese are needed to convert all platelet phases to small star-like intermetallics. A power equation describes the relation between sludge formation temperature and iron content. The volume percentage of intermetallic compounds increases as the iron or manganese content increases. The amount of intermetallic can be estimated from a linear segregation factor.