Effect of antimony on the phase equilibrium of binary Al---Si alloys

Small additions of antimony to eutectic Al---Si alloys cause an increase in eutectic undercooling. The undercooling results in a eutectic with primary α---Al in its microstructure. The metastable Al---Si phase diagram is constructed in order to explain the undercooling and the existence of α---Al in the microstructure. A method of calculating the undercooling, ΔT, from fα, the volume fraction of α---Al in the microstructure, is given. The ternary Al---Si---Sb phase diagram is calculated. From the ternary system it is possible to predict overmodification of Al---Si alloys is caused by the formation of the compound AlSb.