Effect Of AC Magnetic Field On Thermoelectric Power And Microstructure Of Al-Fe Alloys

The solidification microstructure of metal materials affected by the AC magnetic field is related to the nucleation and growth behaviors in the solidification process,while the latter are determined by the melt microstructure.Therefore,it is necessary to study the influence of AC magnetic field on the melt structure.The previous study shows that thermoelectric power,as a sensitive physical parameter of the structure,can be used to study the microstructure of metallic melt.This paper investigates the physical nature of Al-Fe alloys' microstructure affected by the AC magnetic field through measuring the thermoelectric power of Al-Fe alloys melt in the AC magnetic field,as well as the observation of the rapid solidification microstructure of the melt.It shows that thermoelectric power is the sensitive physical parameter of melt structure,which can be used to characterize melt structure changes.Therefore,two aspects are studied with three different components of the Al-Fe alloy.Firstly,thermoelectric power and rapid solidification microstructure of the melt affected by AC magnetic field at different temperatures;Secondly,thermoelectric power and rapid solidification microstructure of the melt affected by different intensity and different frequency of AC magnetic.With XRD and hardness analysis,the influence of AC magnetic field on the melt structure of Al-Fe alloy was explored.Conclusions are as follows:(1)It proposes a hypothesis of cluster structure in Al-Fe alloy melt,which claims that the influence of AC magnetic field on the metal structure in Al-Fe alloys is based on the change of the outer electric layer structure of clusters.The change of clusters' electric layer enables the clusters to adsorb the atoms around them and reorganize of clusters.There are two types of reorganization:those do not meet the magic number characteristics will revert to the original state after closing the AC magnetic field;those meet the magic number characteristics will not revert.(2)The AC magnetic field has no influence on thermoelectric power of solid state Al-Fe alloy,while it has a significant effect on the thermoelectric power of Al-Fe alloy melt.The influence of the structure of the Al-Fe alloy melt in the AC magnetic field can be characterized by the following characteristic parameters:lasting change amount of thermoelectric power,?S(t1),can characterize the lasting change of the structure of metal melt in the AC magnetic field;the residual quantity,?S(t2),can characterize the residual variation of the structure of metal ingots affected by the AC magnetic field;recovery time,At,is used to show the stability of melt structure in the AC magnetic field.(3)In total,three characteristic parameters of thermoelectric power shows a trend of first rising then declining with the increase of the temperature,while the corresponding maximum value varies depending on the Fe content in the alloys.For the Al-0.99%Fe hypoeutectic alloy,with the increase of temperature,the characteristic parameters of the alloy have a maximum value at 673?.For the Al-2.89%Fe hypereutectic alloy,a maximum value is at 710?.(4)The thermoelectric power of Al-Fe alloys in the AC magnetic field has a corresponding relationship with the rapid solidification microstructure.With the variation of thermoelectric power increases,the refinement of the rapid solidification microstructure improves.This shows that the variation of thermoelectric power can be used to characterize the metal structure of Al-Fe alloys.(5)With the increase of the intensity of AC magnetic field,the influence of the AC magnetic field on the melt structure of these three Al-Fe alloys also gradually increases.With the increase of magnetic field frequency,the influence of the magnetic field on the melt structure first increases then decreases,and there is a maximum value related to the Fe content.The possible cause for this phenomenon can be explained from two aspects:on one hand,the higher the frequency is,the shorter the response time will be;on the other hand,the higher the frequency is,the more significant the skin effect will become,thus the interaction range of AC magnetic field becomes smaller.