冷铁对铝合金铸件二次枝晶间距的影响

研究了冷铁厚度、冷铁的有效作用距离、铸件二次枝晶间距以及铸件的模数之间的关系。结果表明，随着冷铁厚度的增加，试样的二次枝晶间距减小；试样的直径和冷铁的厚度显著影响冷铁的有效作用距离，随着试样直径的增加，必须相应增加冷铁的厚度。根据研究结果，绘制了铸件模数、铸件热节厚度及应加冷铁厚度之间的关系诺模图。还研究了冷铁厚度与局部凝固速度及铸件二次枝晶间距之间的关系，并给出了局部凝固速度及铸件二次枝晶间距之间关系的数学表达式，对于任何模数的A357合金铸件，只要合理控制其局部凝固速度，即可得到需要的二次枝晶间距。

Effect of Chill on Secondary Dendrite Arm Spacing of Aluminum Alloy Casting

The relationship of the thickness and effectively acted distance of the chill with secondary dendrite arm spacing and casting mod ulus was investigated. The results indicated that the secondary dendrite arm spa cing of casting sample decre ased with the increase of chill thickness. The specimen diameter and the chill t hickness significantly influenced the effective functional distance of chill. Wi th the increase of specimen diameter, the chill thickness should be increased.Th e network diagram for relationship among casting modulus, thickness of cas ting hot spot and required thickness of chill was plotted.The relationship of chill thickness with secondary dendrite arm spacing and loca l solidification rate was studied. The mathematical expression for relation betw een local solidification rate and secondary dendrite arm spacing was built. It c ould be concluded from the expression that the required secondary dendrite arm s pacing could be attained for any modulus of A357 alloy castings when the local s olidification rate was rationally controlled.