Research The Technology Of Control Newborn Silicon Shape In Different Content Of Si Of Hypereutectic Aluminum-Silicon Alloy

Hypereutectic aluminum-silicon alloy is an important casting alloys and an excellent wear-resistant material.However,the casting of hypereutectic Al-Si alloys always present relatively coarser and brittle primary silicon particles with shape angle which degrade significantly mechanical properties,and limit the further application.In order to improve the primary silicon morphology,it has been studying effective ways to improve the shape of primary silicon in hypereutectic aluminum-silicon alloy and optimizing eutectic structure,and researching in addition of modifiers,heat treatment,rapid solidification and so on.But it cannot be realized in industry.This research has studied systematically on the influences of casting processing,modification processing,solution treatment and reheating treatment on the size and morphology of primary silicon particles in different content of Si of hypereutectic Al-Si alloy based on the prior work.So as to find a process of farthest improving morphology of primary silicon and simple,reliable,and economical.Several phenomenons can be observed in this research.Although primary silicon particles can be fined greatly with the increase addition of modifiers,their sharp angle cause stress concentration easily,and dissevered the Al matrix;moreover,the excessive amount of modifiers cause deteriorating primary silicon.When processed by solution treatment,eutectic silicon particles can be granulated and spheroidized obviously,while the shape angle presenting in the primary silicon will disappear with the increase of both solution temperature and holding time.However,too higher temperature and too longer holding time will lead to the coursing of primary silicon particles,which will be detrimental to the morphology of silicon particles.The primary silicon can be spheroidized obviously by the effect of reheating treatment,but the effect dependent largely on the origin morphologies of particles.And while the technology is not appropriate,the shape of primary silicon will be deteriorated instead of improving.Finely,the best parameter is:for Al-20Si alloy,the best parameter is preheating mold in 150℃,and pouring in 760℃,add 0.4%CUP14 in Al-20Si alloy,reheating samples in 585℃×10min after 24hours heating preservation in 550℃;for Al-25Si alloy,the best parameter is preheating mold in 125℃,and pouring in 810℃,add 0.8%CUP14 and 0.6%RE in Al-25Si alloy,reheating samples in 625℃×10min after 36hours heating preservation in 525℃;for Al-30Si alloy,the best parameter is preheating mold in 125℃,and pouring in 870℃,add 0.8%CuP14 and 0.9%RE in Al-30Si alloy,reheating samples in 640℃×15min after 48hours heating preservation in 525℃.Primary silicon will be spheroidized obviously under these processes,and the processing effect of this route is very splendid.