MODIFICATION OF AL SI ALLOYS - MICROSTRUCTURE, THERMAL-ANALYSIS, AND MECHANISMS

In aluminum-silicon cast alloys, the shapes of the silicon phase and t he general solidification pattern can be changed by the cooling condit ions and by minor additions to the melt. The minor additions either mu se modification (sodium, strontium, and other metals) or refine the pr imary silicon in hypereutectic alloys (phosphorus and elements of Grou p V-B). Detailed examination of the modified microstructures and analy sis of cooling curves are compatible with a modification mechanism inv olving growth rather than nucleation kinetics.