Abstract:
The microstructure and micro-area chemical composition of central-line segregation in magnesium alloy cast-rolled strip were investigated by optical microscopy, scanning electron microscopy, etc. The heat transfer in solidification process and flow process were analyzed by finite difference method. Based on the above, the forming reasons and control method of central-line segregation in magnesium alloy cast-rolled strip were analyzed. The results indicate that solute elements of Al and Zn were enriched and Mn was diluted in the central-line segregation area. The area's microstructure was composed of equiaxed grains with fine size. During the casting and rolling process, magnesium alloy melt nucleated on the roll surface and formed developed columnar crystals along the heat transfer direction. Solute redistribution occurred at the solidification interface. The solute was enriched at the solidification front, particularly at the freezing point. Central-line segregation was formed during the subsequent rolling deformation process. The casting and rolling speed markedly affected the heat transfer and flow in solidification process. The central-line segregation could be controlled by adjusting casting and rolling speed to control the freezing point in a proper location because the overheated melts supplied by feed tip could caused the re-melt of the solidification front and the forced convection, and thus improved the diffusion condition of solute elements during the casting and rolling process.