Study On Microstructure Evolution Of Mushy Zone During Solidification Of Al-Ni Alloy Under High Magnetic Fields

There must be a region in which liquid and solid coexist corresponding to the solidification interval in the solidification process of alloy,due to external temperature gradient,called mushy zone.Present studies have shown that the formation and evolution of solidification structure in mushy zone will affect the morphology,size,solute distribution and precipitation characteristics of subsequent alloy microstructure.Furtherly,the final properties of the material will be affect.High magnetic field is a non-contact controllable high-energy physical field,it can effectively control the fluid and solute migration and redistribution in the solidification of alloy.Therefore,this research takes Al-18at%Ni alloy as the research object and does the experiment of quenching after thermal stabilization in a high magnetic field by controlling the magnetic field parameters and thermal stabilization time.The solidification microstructure evolution and mechanism of the mushy zone under high magnetic field are investigated.Results show that:The high magnetic field effectively changes the morphology and distribution of the microstructure in the mushy zone.On the one hand,Due to the coupling of the thermal electromagnetic force(TEMF)and the magnetic force,the Al3Ni phase in the peritectic phase mushy zone changes from lath to irregular agglomerate.Inside,and a large number of liquid micelles in rich of Ni atoms unevenly distribute in the peritectic phase mushy zone.On the other hand,the Al3Ni2 phase in the primary phase mushy zone is irregular island shape.Due to the thermal electromagnetic convection(TEMC)and the magnetic force,the Al3Ni2 phase changes from a uniform distribution to a segregation under a high magnetic field.High magnetic field significantly changes the morphology of the TP interface.The magnetic field gradient affects the magnetization of Ni atoms,which enriches a large number of Ni atoms at the front of the Tp interface,causing the re-melting and solidification of the tissues on both sides of the TP interface,which leads to the change of TP interface morphology.In addition,the difference in magnetic field strength and thermal stabilization time makes the TP interface morphology irregular and complex.High magnetic fields significantly change the length of the mushy zone.For the peritectic phase mushy zone with relatively few liquid,the high magnetic field mainly affects the length of the peritectic phase mushy zone by competitive effect between TEMF and the Lorentz force.For the liquid-rich primary phase mushy zone,the high magnetic field mainly affects the solute migration,causing the melt to strongly disturb in the direction of temperature increase and the solid phase cannot be stably suspended to migrate,thereby changing the length of the mushy zone of the primary phase.The high magnetic field effectively changed the distribution of Al3Ni phase and solute atoms in the mushy zone.It is showed a corresponding relationship with the evolution and distribution of solidification micro structure in the mushy zone,indicating the effect of solute migration and redistribution on the microstructure evolution of the alloy solidification.