Research On The Purification Technique Of Melt Under Traveling Magnetic Field

A kind of hypereutectic aluminum silicon alloy (Al-20wt%Si) was used asexperimental material in the thesis. Primary silicon particles precipitating from thesolidification process of hypereutectic Al–Si alloy were considered as nonmetallicinclusions. The influence of current, frequency and process-time parameter ofdownward traveling magnetic field (TMF) to the migration and distribution ofnonmetallic inclusions are researched. A new TMF electromagnetic purificationtechnique of metal melt is proposed and the mechanism of this technique isinvestigated.The research discovers that:(1) the damping property of downward TMF causesthe distribution of magnetic induction and electromagnetic force is inhomogeneous indirection of radial. So there exists a pressure difference in melt. Then a rotational flowwill be induced in melting alloy. This forced flow makes an important influence on themigration and distribution of primary silicon particles.(2) A downward TMF can inducea downward flow adjacent to the cylinder and an upward central flow. Thereforeprimary silicon particles are tending to be driven to the top of the sample by the upwardflow, captured and accumulating in the top area.(3) Increase the current equals toenhancing magnetic induction, accordingly electromagnetic force in direction of radialwill increase in linearity. Therefore the degree of unevenness of electromagnetic forceincreases, which means enhancing the stirring of molten alloy.(4) Increase thefrequency of downward TMF will reduce penetration of electromagnetic force.Therefore increase the unevenness of downward TMF and driven flow.(5) Themigration and accumulation of primary silicon particles need a period of time toaccomplish.The research indicates that:(1) use of driven flow caused by downward TMF caneliminate nonmetallic inclusions particles from metal melt effectively.(2) Increase thecurrent of downward TMF can enhance driven flow of melt notably, and then improvethe purification efficiency. But with the increasing of current, the improving trend ofpurification efficiency will decline gradually.(3) Increase the frequency of downwardTMF can also enhance driven flow of melt and improve the purification efficiency.However, when the level of current is too high, increasing frequency will reduce the purification efficiency.(4) When the current and frequency of downward TMF isenough, increasing the handling time of downward TMF can make the migration andaccumulation of inclusion particles sufficient. Therefore increase the handling time canimprove the purification efficiency.