Interfacial tension, wetting and nucleation in Al–Bi and Al–Pb monotectic alloys

Microstructure of the Al 91Pb 9 (wt.%) alloy is improved by addition of TiB 2 particles that stimulate nucleation of the minority phase (Pb) droplets. Reduction in the nucleation barrier for the droplets results in a significant increase in the number of Pb-rich particles, and in a decrease of their size, upon solidification. The key physical parameters for nucleation of a second liquid phase in Al–Bi and Al–Pb monotectic liquids have been measured. The density of coexisting liquid phases, the interfacial tension between them, and the contact angle of the liquid–liquid interface on ZrO 2 and TiB 2 ceramics have been determined as a function of temperature. The contact angle data suggest that Al 2O 3, ZrO 2, and TiB 2 particles can act as centres for heterogeneous nucleation of the minority liquid phase in Al–Pb and Al–Bi immiscible alloys. Casting experiments on the alloy Al 91Pb 9 (wt.%) show that the maximum size of the liquid phase droplets decreases, and their population increases, upon addition of inoculants.