The Influence Of Magnetic Field On Diffusion Behavior In Mg-Al Diffusion Couple And Annealing Process In Commercial Pure Aluminum After ECAP

As a significant physical field,magnetic field has been widely applied to control material structure.Combined with the traditional process,it can be used to prepare advanced material and develop new technology,manufacture better-performing products consequently.Diffusion is the main way to be transportation of substance,the microstructure and performance of material could be improved by means of effective control of the diffusion of atoms.Various metallurgical phenomenon,such as solid phase transformation,recrystallization,grain boundary migration,are closely related with the diffusion of atoms.The magnetic fields affect on these process significantly.Therefore,a detailed discussion of the effects of magnetic fields on the diffusion behavior is the precondition and foundation for the control of microstructure using a magnetic field.Mg-Al diffusion couple and commercial pure aluminum after ECAP are chosen as experimental material.The Mg-Al diffusion couple are treated under pulsed magnetic field and high magnetic field in different heating treatment conditions.The commercial pure aluminum after ECAP are annealed with pulsed magnetic field.We researched the effect of pulsed magnetic field and high magnetic field on atomic diffusion by analyzing the diffusion layer thickness,in addition,we also studied the effect of pulsed magnetic field on annealing processing in commercial pure aluminum after ECAP by analyzing the recrystallized microstructure and grain boundary structure.The growth of interphase layer formed in Mg-Al diffusion couples is studied under different magnetic field strength and temperature.Experiment results show that β(Al3Mg2)and γ(Al12Mg,7)still exist in the interface after annealing either with or without magnetic field.When the Mg-Al diffusion couples are treated under pulsed magnetic field,the higher the annealing temperature,the longer the annealing time,the greater the diffusion layer thickness.And the thickness data analysis indicates that they all grow in accordance with the parabolic law.Comparing with the case of conventional conditions,calculated data indicate that pulsed magnetic field has little influence on the interphase layer growth active energy Q.The results was that pulsed magnetic field increased the effective diffusion coefficient k by increasing diffusion constant k0,therefor promoted the growth of Mg-Al interphase layer.When high rmagnetic field is a positive gradient,it plays a promoting role of diffusion,and the bigger the gradient,the more obvious the effect of promotion;when high magnetic field is a negative gradient,it plays a inhibition role of diffusion,and the bigger the gradient,the more obvious the effect of inhibition.When the magnetic field is a positive gradient,there is an optimal value of 6T that the strength of the magnetic field’s effect on diffusion;when a strong magnetic field is a negative gradient or in the Omm position,in its inhibitory effects on the diffusion that 3T is the strongest,followed by 6T,12T.The recrystallized structure of commercial pure aluminum after ECAP was researched under pulsed magnetic field by optical microscopy and TEM analysis.Comparing with the case of conventional conditions,pulsed magnetic field promotes the process of commercial pure aluminum recrystallization and increases the trend of grain growth.The reason is that magnetic field boosts dislocation release at its pile,thereby accelerating the mobility of dislocation and grain boundaries,and increasing the driving power of grain boundary migration.With the increase of annealing temperature and time,the trend of grain growth are becoming weaker.As can be seen from the TEM analysis of commercial pure aluminum,the pulsed magnetic field has litter effect on the size of subgrain,but it reduces the dislocation density and make grain boundary more clearly and straightly.