Understanding the Interactions of Grain Refiner Particles and Double Oxide Films in Liquid Aluminum Alloys

Recent studies revealed that the addition of different grain refiner master alloys can affect the sedimentation and thus the spatial distribution of double oxide films in the melt. In this work, the interactions of TiB 2 and (Al,Si) 3 Ti particles with bifilm defects were investigated in the case of a liquid Al-Si-Mg-Cu alloy. The interactions between refiner particles and bifilms were studied by optical and scanning electron microscopy (SEM), while the changes in melt quality were analyzed by the computed tomographic (CT) analysis of reduced pressure test (RPT) specimens. The sedimentation behavior of grain refiner particles was investigated through computational fluid dynamics (CFD) simulations. It was found that TiB 2 particles tend to adhere to double oxide films suspended in the liquid metal, while (Al,Si) 3 Ti particles became attached to bifilms due to the heterogeneous nucleation of (Al,Si) 3 Ti on bifilms and the partial engulfment of oxide film segments during the growth of (Al,Si) 3 Ti particles. The attachment of grain refiner particles to double oxide films leads to the aided sedimentation of bifilms, which results in lowered porosity in RPT specimens. CFD simulations revealed that the experimentally observed fast sedimentation of TiB 2 can only be expected when relatively large particle agglomerates are created.