Determination of the average nucleation undercooling of primary Al-phase on refining particles from Al-5.0 wt percent Ti-1.0 wt percent B in Al-based alloys using DSC

摘要

The understanding and control of the transition from columnar to equiaxed growth (CET) is an essential issue according to the desired usage properties. In Al-based alloys, refiners are routinely added to favor equiaxed growth. In that case, equiaxed grains nucleate preferentially on the refiners and can compete with columnar grains. To predict CET, two main parameters have been studied in models: the particle density, N_0 and the nucleation undercooling of the refining particles (DELTA T_N). We have used DSC successfully to measure the critical value of the nucleation undercooling. Thanks to these results, the efficiency of the specific refining particles (Al-5.0 wt percent Ti-1.0 wt percent B) in refined Al-3.5 wt percent Ni alloy has been proved. Additionally, these measurements clearly point out the lowest efficiency of the same particles in refined Al-7.0 wt percent Si which is generally admitted to be due to a Si-poisoning effect. More generally, the nucleation undercooling measured can be used in models dedicated to the quantitative prediction of CET.