Formation of Primary TiAlSi Intermetallic Compounds in Al-Si Foundry Alloys

摘要

It is common practice to add Ti to Al-Si foundry alloys because of its potential grain refining effect. However, an excess of Ti may cause the precipitation of primary TiAlSi coarse particles in the cast microstructure. The present paper describes work conducted to better understand the formation of primary TiAlSi compounds and the resulted cast microstructure. The precipitation temperature of primary TiAlSi intermetallics and the solubility limit of Ti in Al-Si alloys were investigated using thermodynamic calculation, metallographic examination and by LiMCA detection. The impact of the Ti level and cooling rate on the formation and growth of intermetallic particles was experimentally evaluated. The variation of the particle morphology and composition in the cast microstructure were described. The growth of TiAlSi intermetallics in a DC casting of alloy A356 was demonstrated by a decanting method.