Enhanced Heterogeneous Nucleation by Pulsed Magneto-Oscillation Treatment of Liquid Aluminum Containing Al3Ti1B Additions

Pulsed Magneto-Oscillation (PMO) promoted additional nucleation of commercial purity Al containing a range of Al3Ti1B master alloy resulting in a finer grain size. The grain density significantly increased with PMO treatment for all Ti contents. With PMO treatment the grain density is directly proportional to the amount of master alloy added and therefore the number of TiB₂ particles implying that the TiB₂ particle density had a major effect on refinement. The grain density almost doubled (from 307.4 to 507.2 mm^-3) after PMO treatment at a normal commercial level addition of 1 000 parts per million (ppm) Ti by weight, and which increased from 499.5 to 941.1 mm^-3 when 2 000 ppm Ti was added. It is proposed that PMO treatment significantly enhanced the nucleation capacity for TiB₂. In contrast, without PMO treatment, the grain size follows a linear relationship with the inverse of the growth restriction factor (1/Q) indicating that Ti solute also has a significant effect on grain size. Since the cooling conditions were similar for both with and without PMO treatment, the convection generated by PMO produced a more uniform temperature field throughout the melt that promoted the transport and survival of grains contributing to a finer grain size. Pulsed Magneto-Oscillation (PMO) can significantly reduce the grain size of commercially pure Al containing a range of Al3Ti1B mater alloy. The grain size dose not follow a linear relationship with 1/Q after PMO. The grain density is largely increased by PMO and directly proportional to Ti content.