Study On Segregations In 2A14 Aluminium Alloy Hollow Ingots By Electromagnetic Stirring

Aluminum alloys have been widely used in the industrial field due to their low cost,high performance,and ease of production.The DC casting method plays an important role in the production of high-strength aluminum alloy ingots.The detrimental defects like coarse microstructure,uniformity chemical compositions and hot tearing,often occurred in those prepared by the conventional DC casting.In order to improve the quality of the ingots,the applied filed measurements are taken to obtain the better quality in DC casting.The annular electromagnetic stirring(A-EMS)is widely used in preparing high strength aluminium alloy ingots.Large-sized aluminum alloy ingots are often used to produce the large-sized structural forged ring pieces through a series of processes.In order to improve the quality of processed ring pieces,shorten the processing,and save costs,DC casting methods are used to prepare aluminum alloy hollow ingots.In this study,the conventional DC casting and the EMS DC casting are both considered,the numerical models to simulate the 2A14 aluminium alloy large-sized Φ730/0340 mm hollow ingots by conventional and EMS DC casting are established,the numerical simulations of the electromagnetic field,temperature field,the profile of sumps and the flow field are studied.In the numerical simulation study of the conventional and EMS DC casting,the electromagnetic field and macrophysics in the hollow ingots are investigated.It indicated that after the applying of EMS,the magnetic field in the melt is mostly distributed on the surface of the ingots,the magnetic induction dramatically reduced in the radial direction from the ingots outer surface to the inner.The Lorentz force generated in the melt creates forced convection in the melt,and the application of electromagnetic stirring treatment not only greatly improves the uniformity of the overall temperature field,but also significantly reduces the depth of the sump.In the observation of the microstructure in the conventional and EMS DC casting hollow ingots,with the application of EMS,the significant grain refinement can be found,the average grain size obviously decreases from 115 μm to70 μm,more equiaxed grains can be observed instead of coarse-cell grains or dendrites,and the difference of the average grain size distribution along the radial direction of hollow ingot with EMS is more even;the amount of non-equilibrium eutectics reduced by about 21%with EMS,and the size is significantly reduced,and the distribution is more uniform;after the EMS is applied,the microsegregation extent of Cu element is reduced,the solubility of Cu element in the a-Al increases,the concentration of Cu in the non-equilibrium eutectic decreases,and the effective partition coefficient of Cu element increases during solidification;the macrosegregation patterns of conventional and EMS hollow ingots are both following the similar trend that positive segregation occurred in inner sub-surface and center section,meanwhile negative segregation occurred in the section offset to inside of centerline and outer surface area,and it should be noted that there is severer macrosegregation occurred in the EMS hollow ingot than that in the conventional one.The electromagnetic stirring treatment increases the cooling rate of the solidification front by promoting heat distraction in the melt,thereby improving the uniformity of the melt temperature field and composition field,providing greater undercooling for grain nucleation,and promoting the occurrence of heterogeneous nucleation.It effectively increases the nucleation rate,then the grain structure is significantly refined,the solubility of Cu element in the grain significantly increases,and the microsegregation is improved.