Effect of Al-3 wt% Al2O3 master alloy fabricated by calcined kaolin on grain refinement and mechanical properties of A356 alloy

Abstract In the present study, Al-3 wt% Al2O3 master alloy was successfully prepared by the reaction between calcined kaolin and aluminum melt, combined with mechanical stirring and high-energy ultrasonic dispersion technology. The γ-Al2O3 particles produced by the reaction are uniformly dispersed in the matrix, and the average size of γ-Al2O3 is about 65 nm. The refinement effect of Al-3 wt% Al2O3 master alloy on A356 alloy was studied. It was found that the α-Al grain size in A356 alloy refined by Al-3 wt% Al2O3 master alloy was decreased from 980 ± 155 µm to 337 ± 95 µm. Compared with the Al-5Ti-1B master alloy, Al-3 wt% Al2O3 has a higher refinement efficiency. In addition, the refinement efficiency of the Al-3 wt% Al2O3 master alloy will not fade within 60 min. Transmission electron microscope analysis showed that the orientation relationship between γ-Al2O3 and Al was (22−2)γ-Al2O3[011]γ-Al2O3//(11−1)Al[011]Al, which demonstrated that γ-Al2O3 could be used as heterogeneous nucleation sites to refine α-Al grains. Moreover, the tensile properties of A356 alloy had been significantly improved.