This study investigates the microstructural variation in the hypereutectic Al-Si strips produced by the unequal-diameter twin-roll strip casting process. Experimental parameters include the silicon content (13wt% ∼ 20wt%), roller speed (10.0 m/min ∼ 30 m/min), pouring temperature (580 °C ∼ 660 °C), contact angles (22° ∼ 45°), and the addition of the refining elements (Ti, B and P). The solidification structure of hypereutectic Al-Si strip is a multi-layer structure, and two kinds of matrix microstructure can be observed in the refined strip; namely eutectic and off-eutectic structure. The off-eutectic structure (Al-dendrites and granular eutectic silicon) is distributed near the strip's surface, and the eutectic structure (equiaxed Al-grain and acicular eutectic silicon) is located in the centre of strip. Due to the formation of the off-eutectic structure near to the top surface, the primary silicon particle is constrained in the subsurface of the refined strip. In addition, the primary silicon particles of refined strip disperse more uniform than the unrefined strip. According to the above results, the top surface of the refined strip is more smooth than the unrefined strip.
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