Grain Refinement of Aluminum Cast by Heterogeneous Nucleation Sites of L12 modified Al3TiWednesday (08.11.2017) 12:20 - 12:40 Part of:
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 alpha Al grains. It is known that the shape of Al3Ti particles in the Al-5 mass% Ti ingot is platelet and the face of Al3Ti platelets is a (001)Al3Ti plane. However, the dominant face of Al3Ti platelets is not the best plane for heterogeneous nucleation, since it has the largest planar disregistry value among several orientation relationships.
Alternatively, we propose to use of L12 modified Al3Ti particles for heterogeneous nucleation sites. It is known that alloying with a certain amount of a transition element, such as Cr, Mn, Fe, Co, Ni, Cu causes the transformation from the D022-type tetragonal structure of Al3Ti to a high-symmetry L12 cubic structure. This transformation increases the crystallographic symmetry of Al3Ti intermetallic compounds, which results in the constant lattice registry with the metal matrix when they are used as heterogeneous nucleation sites. Moreover, since the lattice constants of some L12 modified Al3Ti are very close to that of Al, it is expected that the L12 modified Al3Ti will become favorable heterogeneous nucleation sites for an Al cast.
In this study, the effects of Al2.5Cu0.5Ti, Al2.7Fe0.3Ti and Al2.7Ni0.3Ti particles with L12 structure on grain refining performance were studied. It is found that the L12-type Al2.5Cu0.5Ti, Al2.7Fe0.3Ti and Al2.7Ni0.3Ti particles can become favorable heterogeneous nucleation sites for the Al cast, since the disregistry between Al2.5Cu0.5Ti, Al2.7Fe0.3Ti, Al2.7Ni0.3Ti and Al is small.