Grain Refinement of Cast Aluminum by Heterogeneous Nucleation Sites

Grain refinement plays a vital role in cast and wrought Al alloys. To achieve a grain refined cast microstructure, addition of Al-Ti, Al-Ti-B, and Al-Ti-C refiners has become a common industrial practice. The refiners introduce a large number of particles such as Al₃Ti, TiB₂, or TiC into the Al melt, and these particles act as heterogeneous nucleation sites for α-Al grains. In this article, some of the main theories of grain refining by refiners, and the crystal structure and shape of Al₃Ti in Al-Ti refiner are briefly summarized to outline the physical aspects of grain refinement. Then, our results on grain refining performance of pure Al casts by equal-channel angular-pressed Al-11vol%Al₃Ti refiner, cold-rolled Al-11vol%Al₃Ti refiner, Al-10vol%Ti refiner, and Al-10vol% L1₂-type Al_2.7Fe_0.3Ti refiner will be described. Fragmentation behavior of Al₃Ti platelets in Al-Ti refiner by friction stir processing is also presented.