Critical temperature for grain refining of primary Si in hyper-eutectic Al-Si alloy with phosphorus addition

The relation between the casting temperature and the size of primary silicon particles of hyper-eutectic Al-Si alloys was studied to understand the behavior of phosphorus in the melt, when phosphorus is added, primary silicon particles are refined as long as the casting temperature exceeds the temperature T, defined as the critical temperature for grain refinement T is expressed as T(K) = 23 × Si(mass%) + 630. However, they are coarsened as the casting temperature decreases in the temperature ranges between T and liquids, when phosphorus is added, the grains are not refined and are not affected by the casting temperature. Temperature T is considered as the temperature at which AlP compounds begin to grow and agglomerate, and it is a useful index for determine the casting temperature.