Microstructural Changes on a Ternary Al–Cu–Si Eutectic Alloy with Different Pre-heated Mold Temperatures

Abstract

In order to understand the solidification behavior and microstructural evolution of the Al–Cu–Si ternary eutectic alloy system, the evolution on the microstructure of the Al–Cu–Si ternary eutectic alloy with different pre-heating mold temperatures was investigated. When the mold was preheated at 500 °C, the primary Si and Al2Cu dendrites were mainly observed and (α-Al + Al2Cu) binary eutectic and needle-shaped Si phase were also developed. When the mold preheating temperature was 300 °C, the primary Si and Al2Cu dendrites were observed with colonial regions where the (α-Al + Al2Cu + Si) ternary eutectic phase was also present. When the mold preheating temperature was 150 °C, the bimodal structure which composed of (α-Al + Al2Cu) binary eutectic phase and (α-Al + Al2Cu + Si) ternary eutectic phases was observed When the mold preheating temperature was changed from 500, 300, and 150 °C, Si phase undergoes the most distinctive microstructural changes. When it passed the critical cooling rate, the (α-Al + Al2Cu + Si) ternary eutectic was formed. It was concluded that the growth of Si phase was suppressed by the high cooling rate and the growth of Al and Cu containing eutectic phases, which grow cooperatively, were also suppressed. This resulted in the ternary eutectic alloy with a finer microstructure.