Influence of variation in the silicon content on the silicon precipitation in the Al–Si binary system

Abstract

Silicon is a base element used to cast aluminum alloys, and the properties of an Al–Si alloy can be controlled by adjusting the casting and heat treatment parameters. The influence was investigated that the silicon content of Al–Si alloys on the silicon precipitation rate. Silicon was added to pure commercial aluminum at 0.8, 1.5, 3.0, 6.5, and 9.5 mass%, and then, samples were produced through casting. The specimens were solid solution treatment for 10 h at 803 K and were analyzed using a thermomechanical apparatus and differential scanning calorimetry to determine the change of exothermic reaction and the coefficient of thermal expansion (CTE) according to the silicon content in aluminum alloys. The heat flow curve showed an exothermic reaction resulting from silicon precipitation in the matrix, dissolving in the matrix during the solid solution treatment. The CTE curve also indicated silicon precipitation, and the peak value of the CTE reflected the change in temperature at which the silicon precipitation had occurred according the silicon content in the aluminum alloy. The rate of the silicon precipitation appeared to be proportional to the silicon content in the aluminum alloy since the silicon content induced changes in the microstructure of the aluminum alloy and thereby affecting the silicon precipitation kinetics.