FORMATION OF (Can-x,Nax)Pm COMPOUNDS IN EUTECTIC Al-Si PISTON ALLOYS AND INVALIDATION OF PHOSPHORUS MODIFICATION EFFECT
Formation of （Ca n-x, Na x）Pm Compounds in Eutectic Al--Si Piston Alloys and Invalidation of Phosphorus Modification Effect

The influence of Ca and Na on phosphorus modification performance, the relation between constitution of compounds containing-phosphorus and modification performance in eutectic Al-Si piston alloys were investigated by optical microscopy and electron probe microanalyzers (EPMA). It has been shown that Ca or (and) Na can make phosphorus modification inefficiency and even Na modification efficiency appears, the abnormal phenomena is due to the formation of (Can-x, Nax)Pm compounds which is more stable than A1P phases in the melt. However, the phosphorus modification efficiency can recover after refining treatment by C2Cl6, because of (Can-x, Nax)Pm changing to (Al5, Mg0.85, Ca0.15) P3.4 which can serve as the nuclei of primary Si phases.