Effect of cooling rate on modification of eutectic silicon during DC semi-continuous casting of 4032 aluminum alloy billet

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Effect of cooling rate on modification of eutectic silicon during DC semi-continuous casting of 4032 aluminum alloy billet

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WU Yongfu / ZHANG Baocun / WANG Ning / YU Kangcai / ZHU Guanglei

In this work, numerical simulation was used to investigate the distribution of cooling rate during DC semi-continuous casting of 4032 aluminum alloy billets with the diameters of ϕ120 mm, ϕ300 mm and ϕ500 mm. Further, the effect of cooling rate on the modification of eutectic silicon by Sr addition was investigated. The simulation results indicate that the cooling rate from the surface to the center of the billet generally decreases. As the billet diameter increases, the sump depth becomes deeper, the distance between the isothermal lines of liquidus and solidus becomes larger, and the cooling rate at the billet center decreases sharply. The cooling rate affects the modification results of eutectic silicon by Sr addition. When the cooling rate is higher than 1.8 K/s, Sr addition can achieve excellent modification results. However, as the cooling rate decreases, the modification of eutectic silicon becomes worse, even the Sr contents are the same. At the industrial casting conditions, the cooling rates of inner part of the ϕ500 mm billet are below 1 K/s. At this low cooling rate, the Sr content of 0.033%-0.036% is not enough to modify the eutectic silicon any more. To the billet with the diameter as large as 500 mm, the casting speed is the most important factor that influence the cooling rate distribution. But the influenced area is only limited within the distance of R/2 to the surface, and little influence to the center of the billet.