Study On The Refinement Of Primary Si Phase In Hypereutectic Al-Si Alloy By In-sit TiB₂

Hypereutectic Al-Si alloy get excellent wear resistance property for its low density and low thermal expansion coefficient because of the addition of Si.Under conventional conditions,there are coarse primary silicon phase in hypereutectic Al-Si alloy,which seriously separates the alloy matrix,reduces the wear resistance and machinability of the alloy,and seriously restricts the application of the alloy.In this study,TiB₂ particles were synthesized in hypereutectic Al-Si alloy by in-situ method.The effects of TiB₂ particles on the morphology and size of the primary Si phase in hypereutectic Al-Si alloy were investigated.In situ TiB₂ particles were prepared in Al-Si alloy melt by using Al-Ti master alloy and Al-B master alloy as the intermediate alloy method.The TiB₂ particles were refined in the primary Si phase of Hypereutectic Al-Si alloy.Ultra high temperature（1000℃）and low temperature（780℃）the content of TiB₂ in situ under direct in situ 1.3-1.5wt.% range,the average size of Al-20 wt.%Si alloy in early phase of Si crystal is about 50μm;direct in situ mixed fluoride salt by using the method of K2TiF6 and KBF4 in situ TiB₂ particles,high temperature（850℃）and low temperature（780℃）content of in situ TiB₂ was in the range of 1.3-1.5wt.%,Al-20 wt.%Si alloy in the average size of primary crystal phase Si is about 50μm.Al-20 wt.%Si alloy with TiB₂ content of 12 wt.% was prepared by in situ TiB₂ with mixed fluoride method.The Al-Si alloy with TiB₂ content of 1.0-3.0wt.% was prepared.The average size of the primary Si phase in the alloy was refined to about 30μm.The experiment results indicate that the TiB₂ particles are stable in hypereutectic Al-Si alloy,which can act as the nucleation substrate of the primary silicon phase and so refine the primary silicon.TiB₂ does not affect other elements to modify the eutectic silicon in the alloy for its stability.The test shows that by in situ mixed villiaumite authigenic high volume fraction of 12 wt.% TiB₂,the diluted TiB₂ of Hypereutectic Al-Si alloy in early grain refinement of Si phase,at the same time,the Sr of the eutectic Si Al-Si eutectic alloy is refined,the hypereutectic Al-Si alloy in the primary Si phase the eutectic Si phase to achieve the effect of composite modification.In the range of TiB₂,the average size of the primary Si phase in the Al-20 wt.%Si alloy is about 20μm,and the eutectic Si phase is refined into fine particles of 1.0-3.0wt.%.The experiment results show that the addition of Mn,Cu,Mg,Fe,and other alloying elements in Al-20 wt.%Si-TiB₂ alloy has no obvious improvement on the primary Si phase in TiB₂ alloy.TiB₂ phase density is higher than that of Al-Si phase in Aluminum Alloy melt so gravity segregation may be found,with argon to Aluminum Alloy melt stirring and refining process,can improve the uniform distribution of TiB₂ particles in aluminum melt,TiB₂ particles uniformly distributed ingot.In-situ TiB₂ particles can refine the primary silicon phase of the hypereutectic Al-Si alloy in conventional casting temperature range,and it does not need high temperature casting,and does not affect the refinement effect of modification elements on eutectic silicon,at the same time,this method can achieve the effect of composite modification.