HYPEREUTECTIC Al-Si ALLOY CASTINGS WITH A COMPLETELY EUTECTIC STRUCTURE

摘要

Experiments with electrolytic Al-Si alloy (DEASA) were conducted to produce the pure eutectic structure without impurity-addition in hypereutectic alloys castings at same cooling rate. Until silicon increased to 16% the coupled eutectic was achieved, accompanying a decrease in undercooling in freezing. This is associated with the inheritance of the self-modification of DEASA. With 17% Si the self-modification disappeared and the coarse primary silicon crystal occurred under undercooling of 5°C. The reason to develop the coupled eutectic structure seems to be attributed to the suppression of silicon growth in cooling range before approaching the apparent eutectic temperature by large undercooling rather than the competitive growth between two phases in eutectic.