Effect of Cu content on grain refinement of an Al-Cu alloy with AlTi6 and AlTiB1 refiners

To reveal the effect of Cu content on the grain refinement of aluminium alloys, commercial Al-Cu alloys with a Cu contents from 0 to 6.5 % are refined with 0.3% AlTi5B1 (0.015 % Ti, 0.003 % B) and 0.833 % AlTi6 (0.05 % Ti) master alloys. It is found that in the non-refined samples, increasing Cu content can prevent the formation of columnar crystals and reduce the grain size. The grain refinement of both refiners is very efficient for all the Al-Cu alloys. When 0.3% AlTi5B1 is added, the grain refinement becomes more pronounced with increasing Cu content up to 6.5 %. It 0.833 %AITi6 refiner is used, the minimum grain size is obtained in the sample with 3 % Cu, but the refinement seems less sensitive to the Cu content. Many TiB₂ particles are found in the samples refined with 0.3 % AlTi5B1, which may survive the dissolution and serve as heterogeneous nuclei for A-Al, Cu dies not react with TiB₂ particles; therefore, the improvement of the grain refinement by Cu content is mainly due to its contribution to the constitutional undercooling.