Response of an Al—Cr alloy towards grain refinement by Al—5Ti-1B master alloy

Abstract

Grain refining of an Al–2%Cr alloy by Al–5Ti-1B master alloy (5/1 TiBAl) has been studied as a function of the addition rate of the grain refiner in the range 0.2–1.2% and holding times up to 120 minutes. This study revealed that an effective grain refinement of Al–2%Cr requires a minimum addition of 1.2% grain refiner as against the 0.2% which is normally required for most of the conventional Al alloys. The work further revealed that the effect of grain refiner starts fading after holding the melt for about 5 minutes, irrespective of the addition rate of grain refiner. The formation of complex aluminides in the presence of Cr seems to be the primary reason for the poor grain refining response of this alloy at low addition rates of grain refiner. At high addition rates, the better grain refining behaviour of the present alloy was found to be essentially due to the availability of finer unreacted nucleating sites (TiAl₃ and TiB₂).