Hypereutectic Al-Si alloy hollow billets with φ106mm/φ60mm in diameter were fabricated by direct-chill casting.Combined numerical simulation with casting experiments

effects of casting speed on casting process and microstructures of the hollow billet were analyzed.The results reveal that with increasing in the casting speed

the sump depth is increased

and the height and the maximum temperature of remelting layer at the inner wall are increased gradually.When the casting speed reaches 240 mm/min

a significant Si-deplete layer is formed at the inner wall

which is attributed to the melt convection at the solidification front.When the casting speed reaches a certain value that the absorption ability of Si atoms or cluster is the lower than that of breaking away at the solidification front

the Si-deplete layer can be formed.