Effects of Thermalrate Treatment Technique on Microstructure and Mechanical Properties of Hypoeutectic Al–Si Alloys

Abstract

In this study, effects of thermalrate treatment (TRT) technique on microstructure and mechanical properties of hypoeutectic Al–Si alloys with addition of Ti were studied. The superheating temperatures of the melt were ascertained based on the DSC result. The results show that when the alloy castings in sand mold were treated with TRT technique at the superheating temperature of 930 °C, α-Al changes into smaller equiaxial crystals from coarse dendrites, and hardness of the alloy increases by 12.7 %, compared to that of the alloy treated with conventional casting technique. In addition, the supercooling increases to 8.5 °C and the characteristic temperatures of eutectic solidification are all the lowest with TRT technique at the superheating temperature of 930 °C. As holding time increases at the pouring temperature of 730 °C in TRT at the superheating temperature of 930 °C, the effects on microstructure and mechanical properties of the alloy casting in sand mold decrease. TRT technique plays a limited role in the alloy casting in permanent mold.