Grain refinement mechanism of aluminum by Al-Ti-B master alloys

Abstract

Al-Ti-B type master alloys are routinely added into aluminum for a grain refinement purpose. However, a consensus about the mechanism of grain refinement is still yet to reach. This work is aiming at further understanding the grain refinement mechanism through studying the stability of TiB2 in pure aluminum and TiB2/AbTi interfaces in aluminum by transmission electron microscopic (TEM) techniques. It is found that TiB2 reacts with aluminum forming (Ti,Al)B2 solid solution and releasing titanium into aluminum. A crystallographic orientation relationship exists between TiB2 and AbTi in Al-Ti-B alloys. A dynamic nucleation theory for the grain refinement is therefore proposed as a dynamic AbTi layer in the thickness of a couple of atoms existing on the surface of (Ti,Al)B2 and being responsible for nucleating aluminum grains.