Insights into Poisoning Mechanism of Zr by First Principle Calculation on Adhesion Work and Adsorption Energy between TiB2, Al3Ti, and Al3Zr

Abstract

Al-Ti-B intermediate alloys are widely used as grain refiners in aluminum alloys owing to the presence of Al3Ti and TiB2 phases. However, the existence of Zr in aluminum alloy melts often results in coarse grain size, leading to Al-Ti-B failure called Zr poisoning. There are three kinds of poisoning mechanisms related to TiB2, Al3Ti, and a combination of TiB2 and Al3Ti for Zr. First, Zr forms ZrB2 or Ti2Zr with TiB2 in Al-Ti-B to reduce the nucleation ability. Second, Zr existing in the aluminum melt with a high melting point Al3Zr then attracts Ti to reduce the dispersion of Ti as a growth inhibitor. Third, Zr reacts with Al3Ti on TiB2 surface to form Al3Zr, thereby increasing the degree of mismatch with Al and diminishing the refiner’s ability as a nucleation substrate. To gain a better understanding of the mechanism of Zr poisoning, the first principle was used in this study to calculate the adhesion works (ZrB2//Al3Ti), (Ti2Zr//Al3Ti), (Al3Zr//Al3Ti), (Al3Ti//Al), (TiB2//Al3Zr), and (Al3Zr//Al), as well as the surface energy of Al3Zr and adsorption energies of Al to Al3Ti or Al3Zr. The results demonstrated that Zr poisoning originated from the second guess. Zr element exiting in aluminum melt led to the formation of an Al3Zr (001) surface. The interfacial adhesion work of Al3Zr (001)//Al3Ti (001) was not weaker than that of TiB2//Al3Ti. As a result, Al3Zr first combined with Al3Ti to significantly decline the adsorption of Al3Ti (001) on Al, losing its role as a nucleating agent and grain coarsening. Overall, to prevent failure of the grain refiner in Zr containing aluminum melt, the adhesion work interface between the generated phase of the grain refiner and Al3Zr must remain lower to avoid the combination of the generated phase of grain refiner with Al3Zr. In sum, these findings look promising for evaluating future effects of grain refinement in Zr containing aluminum melt.