Factors affecting the grain-refinement of aluminum using titanium and boron additives

The development of grain-refining techniques for the casting of aluminum, and the results achieved using additions of ternary Al--Ti--B master-alloys, are briefly described. A test procedure is given for assessing the relative effectiveness of these master-alloys, and the results are related to the various kinds of alloy treated, including those with constituents which poison the grain-refining agent. The equilibrium conditions which affect the behavior of the constituents of the grain-refined alloys are examined quantitatively from a thermodynamic viewpoint. One theory about the mechanism of nucleation of aluminum on titanium diboride is examined and found inapplicable. New data on the solubility of TiB2, ZrB2, TiC, ZrC, Cr3C2, and CrB2 in liquid aluminum are presented graphically. Practical aspects of alloy behavior in grain-refining practice are analyzed and discussed on the basis of the quantitative data