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.