Pore morphology of porous Al-Ti alloy fabricated by continuous casting in hydrogen atmosphere

Porous Al-5 mass%Ti alloy was fabricated by unidirectional solidification in hydrogen atmosphere, using a continuous casting technique. The porous Al-Ti alloy was prepared at different transfer (solidification) velocities, and the effect of transfer velocity on the pore morphology was investigated. It was found that the pore shape changes with increasing transfer velocity, while the porosity does not change with increasing transfer velocity. In the case of a low transfer velocity (0.5 mm·min^-1), elongated pores surrounded by the columnar microstructure are formed, which indicates that the pores grow along the solidification direction together with the solid phase. In the case of a middle transfer velocity (5.0 mm·min^-1), elongated pores surrounded by the columnar microstructure and needle or plate-like Al ₃Ti alloys are formed. In the case of a high transfer velocity (10.0 mm·min^-1), spherical pores surrounded by the equiaxed microstructure are formed, because the primary crystals formed in the solidification front prevent the growth of elongated pores. It is suggested that the pore morphology is closely related with the solidification rate.