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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 Al2.7Fe0.3Ti refiner will be described. Fragmentation behavior of Al3Ti platelets in Al-Ti refiner by friction stir processing is also presented.