Crystallography of Zr poisoning of Al-Ti-B grain refinement using edge-to-edge matching model

Abstract

The mechanism of zirconium poisoning on the grain-refining efficiency of an Al-Ti-B based grain refiner was studied. The experiment was conducted by melting Al-5Ti-1B and Al-3Zr master alloys together. The edge-to-edge matching model was used to investigate and compare the orientation relationships between the binary intermetallic compounds present in the Al-Ti-B-Zr system. The results show that the poisoning effect probably results from the combination of Al₃Zr with Al₃Ti and the decreased amount of Ti solute, for Al₃Ti particles have good crystallographic relationships with Al₃Zr. Totally six orientation relationships may present between them, while they play vital roles in grain refinement. TiB₂ particles appear to remain unchanged because of a bit large misfit. Only one orientation relationship may present between them to prevent Al₃Zr phase from forming on the surface of TiB₂, though TiB₂ is agglomerated. The theoretical calculation agrees well with the experimental results. The edge-to-edge matching model is proved to be a useful tool for discovering the orientation relationships between phases.

Keywords

crystallography / Al-Ti-B / Zr / edge-to-edge matching model / poisoning mechanism

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