A novel research on the solute redistribution phenomenon of sub-rapid twin-roll cast Al-50 wt.% alloy treated by semi-solid heat treatment

Abstract In this study, a vertical twin-roll cast (TRC) thermal-fluid coupling model was established to determine a suitable roll-casting velocity. A slab of 0.9mm thick roll-cast Al-50 wt.% Si alloy with a two-phase zone width of 473°C was prepared at a velocity of 20m/min for the first time. In addition, the finite element simulation showed that the average heat transfer rate had a positive correlation with the roll-casting velocity. When the roll-casting velocity increased to 20m/min, the average heat transfer rate reached 1260K/s, at which point, the average size of the primary Si was merely 16.5μm. This was a decrease of approximately 90% when compared with the size of alloys cast with conventional methods. After carrying out semi-solid heating, an observation on the distribution of alloy elements identified a novel phenomenon of solute redistribution, i.e., inverse segregation. This inverse segregation process was highly significant in further controlling solute redistribution in the alloy. Additionally, it provided a new concept for improving roll-cast segregation.