Abstract:Taking Fe, Si, Ga and Zn, whose solute element partition coefficient is less than 1, as the research object, the change of impurity element content during solidification of liquid aluminum under industrial test conditions and the corresponding microstructure (including grain morphology, size and intermetallic compounds) were analyzed. The contents of impurity elements and precipitated phase under Scheil-Gulliver cooling condition calculated by thermodynamic software Factsage were compared. It is found that the content of impurity elements in the solid phase of liquid aluminum is the lowest at the initial solidification stage, and all of them are greater than the theoretical calculated value. With the progress of solidification, the content of impurity elements gradually increases and the deviation from the theoretical value becomes larger and larger. The reasons for the above phenomena include: 1) The boundary layer effect exists in the actual solidification process of liquid aluminum, that is, the impurity elements discharged from the solid phase are not fully diffused into the liquid phase; 2) There is microscopic segregation in the actual solidification process of liquid aluminum, that is, Al-Fe-Si intermediate phase precipitates along the grain boundary. In addition, under the experimental conditions of this study, it is found that the solidification structure includes coarse columnar crystals, fine columnar crystals and equiaxed crystals. The coarse columnar crystals are more beneficial to promote the segregation and purification efficiency of some impurity elements, and the formation of coarse columnar crystals can be promoted by controlling and increasing the cooling intensity.