Modification Performance of the Al-P Master Alloy for Eutectic and Hypereutectic Al-Si Alloys

A new type of Al-2.5%P master alloy has been developed, which can be used to modify eutectic and hypereutectic Al-Si alloys. The modifying performance, the P distribution inside Si phases and modification mechanisms were investigated. It has been found that the Al-P master alloy can remarkably refine primary Si grains in hypereutectic Al-Si alloy and its σ_(b,20℃) and δ_(20℃)can increase by 19.0% and 125% respectively; σ_(b,20℃) and σ_(b,300℃) of modified eutectic Al-Si alloy can increase by 11.1% and 18.9% respectively as result of the appearance of fine primary Si grains and shorter eutectic Si crystals. AIP particles are easily found in the center of some primary Si phases in treated hypereutectic Al-Si alloy, while AIP and dissociative P are observed in Si phase in modified eutectic Al-Si alloy. It is considered that there are two modification mechanisms for eutectic Al-Si alloy, one is heterogeneous nucleation and refining of primary Si phase by AlP particles, and the other is P atoms modify the morphologies of Si phases. The modification for the hypereutectic Al-Si alloy mainly depends on heterogeneous nucleation mechanism induced by AlP particles.