4032铝合金圆锭DC半连铸过程中冷却速率对共晶硅变质的影响

采用数值模拟的方法,研究DC(direct chill,DC)半连铸?120 mm、?300 mm、?500 mm的4032铝合金圆锭在横截面上的冷却速率分布,并进一步研究冷却速率对共晶硅Sr变质效果的影响。研究表明,从铸锭表面至中心冷却速率整体呈下降趋势。随着铸锭尺寸的增大,铸锭的液穴变深,液相线温度与固相线温度的等温线之间的距离变大,铸锭内部的冷却速率显著降低。Sr对共晶硅的变质效果受到冷却速率的影响,冷却速率高于1.8 K/s时,Sr变质可以获得较好的变质效果。随着冷却速率的降低,在Sr含量相同的条件下,变质效果变差。工业生产条件下,?500 mm圆锭内部的冷却速率降低至1 K/s以下,此时含量为0.033%~0.036%的Sr已不能使共晶硅有效变质。DC半连铸工艺参数中,铸造速度对?500 mm铸锭的冷却速率分布的影响程度较大,但也仅影响距离铸锭表面小于R/2以内的冷却速率分布,无法提高铸锭内部的冷却速率。

Effect of cooling rate on modification of eutectic silicon during DC semicontinuous casting of 4032 aluminum alloy billet

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?120 mm,?300 mm and?500 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?500 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.