Refinement Properties and Refinement Mechanism of a New Master Alloy Al-5Ti-1B-1RE Refiner

To obtain high-quality grain refiner, a new Al-5Ti-1B-1RE master alloy grain refiner was synthesized by the melt-matching method. Its microstructure and refining effect, refining properties, and refining mechanism were analyzed. The experimental results show that the second-phase particles of Al-5Ti-1B-1RE master alloy are mainly TiB2, Al3Ti, Ti2Al20RE, etc. The magnitude of the free energy ΔG of the synthesis reaction is calculated to be ΔGTiB2 < ΔGAl3Ti < ΔGTi2Al20RE. The nucleation rate N mainly depends on the kinetic atomic diffusion activation energy Q and the thermodynamic nucleation work. The microstructure of commercial pure aluminum refined by the new grain refiner has almost transformed from coarse columnar crystals to fine equiaxed crystals, with an average grain size of 70.2 μm, which was 36.18% and 20.66% smaller than that refined by domestic and imported Al-Ti-B wire master alloy grain refiner, its mechanical properties of tensile strength σb were increased by 11.94% and 8.29%, and elongation δ was improved by 31.79% and 17.41%, respectively. The main refinement mechanism is the formation of TiAl3 on TiB2 particles and the release of RE atoms from the Ti2Al20RE phase, which in turn is partially transformed into the TiAl3 phase, which promotes dual nucleation refinement.