Grain Refinement of Al4CuTi Based Alloy with Zr, Sc, Er, and TiB2

The refinement of Al alloys has been extensively investigated for several decades both in industry and academia. However, the grain refinement potency by TiB ₂ alone is not high as expected. The presence of other solutes (e.g. Ti) is, therefore, of great necessity to enhance the grain refinement potency of TiB ₂ by tailoring the heterogeneous nucleation interface of TiB ₂. Furthermore, in order to further improve the grain refinement of Al alloys, Sc and Zr were also used together with TiB ₂. However, the addition of Sc with high concentrations is not affordable because Sc is very expensive for a large-scale application in foundry industry. The main aim of this present investigation is to determine an optimum grain refiner for Al4CuTi alloy by using Zr, Sc and Er because Er is less expensive than Sc. A combined addition of Zr and Sc was found to have a significant grain refinement effect on Al alloys rather than Zr or Sc alone, which can be interpreted by the fact that Sc is dissolved in Al ₃Zr phase. In contrast to Sc, Er does not appear to act as an efficient grain refiner because AlCuEr phase forms which didn’t act as an active heterogeneous nucleation site and subsequently didn’t facilitate the grain refinement phenomenon. Finally, a combination of 0.002 wt% TiB ₂ together with 0.1 wt% Sc and 0.15 wt% Er can refine the grain size to about 50 µm, which is beneficial to obtain the better fluidity and reduce the hot tearing of AlCu based alloys.