Grain Refinement Of Primary Si In Hypereutectic Al-Si Alloys Using P-based Master Alloys

Aluminum-based alloys are widely used in the automotive and aeronautical industries due to their high strength-to-weight ratio and high wear resistance.Hypereutectic Al-Si alloys are particularly preferred as they exhibit a low coefficient of thermal expansion and a high temperature-strength.However,the coarse primary silicon phase is prone to premature crack initiation and fracture when subjected to tension loading,which affects the mechanical properties of the alloy negatively.Phosphorous addition is the most common grain refinement method for primary silicon,due to its simplicity and effectiveness.In this study,the grain refinement performances of Si-3P(all composition indicators,such as 3,represent % weight unless otherwise stated),Si-25Mn-10 P and Al-10Si-2Fe-3P master alloys on hypereutectic Al-24 Si alloy were studied by using the optical microscope(OM),scanning electron microscope(SEM),electron probe microanalyzer(EPMA),energydispersive spectroscopy(EDS)and inductively coupled plasma atomic emission spectroscopy(ICP-AES).Holding temperatures of 810oC,820oC and 840oC were used,and holding time was also varied at 30 minutes,60 minutes,and 90 minutes.The main research results obtained in this paper are as follows:The phosphorous-containing compounds in Si-3P,Si-25Mn-10 P,and Al-10Si-2Fe-3P master alloys are SiP,MnP,and AlP compounds,respectively.All three master alloys are good grain refiners for the hypereutectic Al-Si alloy.The average grain size of the primary silicon refined by Si-25Mn-10 P master alloy is about 18?m with a holding time of 30 min,which is significantly better than those of the Si-3P and Al-10Si-2Fe-3P master alloys and satisfying the general expectations for a good master alloy.Higher holding temperature had a positive effect on the grain refinement performance of the Si-25Mn-10 P master alloy.The grain refinement performances of the master alloys showed deteriorating trends with prolonging the holding time.Additionally,the grain refinement mechanism of the three master alloys was revealed.It was concluded that the Si-25Mn-10 P master alloy because the active phase is MnP.Therefore,it does not suffer the challenges suffered by Si-3P or the Al-10Si-2Fe-3P master alloys.