Effect Of Strontium And Cooling Velocity On The Organization And Properties Of Al-16Si Alloy

Hypereutectic Al-Si alloy was widely used because of the low density,high hardness,low linear expansion coefficient,good casting performance advantages,especially in aerospace,railway transportation,military,electronics and internal combustion engine piston manufacturing and other fields,which has broad application prospects.But the massive primary silicon phase in the microstructure significantly reduce its mechanical properties.Eutectic Al-16Si alloy was the research object in this article.In this paper we studied effect of the Sr elements on alloy organization structure and the solidification behavior,and investigated the effect of cooling velocity on the microstructure and hardness of alloy solidification,the solidified structure and discussed the formation mechanism and strengthen the behavior performance.After this research,we got the following conclusions:The simulation results show that when the wt 0.2%and wt 1%of Sr element were add into Al-16Si alloy,respectively,the eutectic point will move to the right and Help to reduce the primary silicon phase.with the increase of Sr content,the eutectic point moves to the right further.The new compound of Al₂Si₂Sr would generate in the microstructure,the solidification organization of Al-16Si-xSr alloy mainly include Al₂Si₂Sr compounds,the primary silicon and eutectic organization.The experiment verified simulation results subsequently.With much amount of Sr was added into the alloy,morphology of primary silicon changed obviously in the Al-16Si-xSr alloy,which changed from the regular plate shape to the irregular Petaloid with many holes in the middle of the grain.The crystal morphology of Al₂Si₂Sr compounds changed form small block to larger rod or stick with the increase of Sr element addition by comparing the rules of Al-16Si alloy,the amount of Al₂Si₂Sr grain increased in the meanwhile.The addition of Sr element has significant influence on the eutectic silicon phase.After the Sr element was added,the morphology and distribution of eutectic silicon in the Al-16Si-xSr alloy has had the obvious difference,changed from bulky,discrete rod into a very thin and small grain spacing coraloid,but eutectic silicon grew up trend was obvious with the increase of addition of Sr;The eutectic reaction was also influenced by the Sr elements and the change of cooling velocity of the alloy.When the quantity of Sr element increased within a certain range,the eutectic point of Al-Si alloy in the phase diagram moved to the right direction,and the proportion of eutectic phase increased in the microstructure of Al-16Si-xSr alloy.The different cooling velocitys have great influence on the primary phase and eutectic microstructure.The size of primary silicon will obviously bulky with the increase of cooling velocity,but the morphology did not change.In the process of solidification,the grain morphology of Al₂Si₂Sr did not change,but the grain size decreased with the increased of cooling velocity.When the cooling velocity of alloy was increased,the eutectic silicon grain growth trends were suppressed,thus the grain size of the eutectic silicon became more fine and with much smaller grain spacing..Besides large cooling speed,can inhibit the formation of primary phase,make alloy eutectic point moves to the right,reducing the precipitation of primary phase,make eutectic phase proportion increases.The results of hardness testing show that the microhardness of eutectic organization increased obviously with the increase of Sr content,Mainly because of grain refinement of eutectic organization and eutectic silicon content increases.Besides larger cooling velocity also lead to the refining of eutectic organization a,the value of microhardness also will increase.