Effect Of Magnetic Field On Precipitation Behavior Of Iron Intermetallic Compounds In Al-Si-Fe Ternary Alloy Via X-ray Imaging

In the process of Aluminum alloy casting and recycling,iron element generally exists as an impurity element.With the solidification process,the thick and hard brittle iron intermetallic compounds(IMCs)are formed.This precipitated phase generally reduces the mechanical properties of the alloy and is the main location of crack initiation and material fracture.Researchers usually control the precipitation of IMCs by controlling the cooling rate and adding microelements to improve the properties of Aluminum alloy materials.Magnetic field(MF),as a non-contact method,is widely used to regulate the formation of microstructure during metal solidification.However,the study of MF to improve the precipitation behavior of IMCs in Aluminum alloys needs further discussion.In this work,Al-Si-Fe alloy is taken as the research object,and synchrotron radiation X-ray tomography imaging technology is used to study the influence of MF on the precipitation behavior and evolution process of IMCs under different cooling rates and solidification methods.The main research results are as follows:When the axial MF is applied in the directional solidification of Al-10 wt.%Si-1wt.%Fe alloy,it is found that the strong MF inhibits the melt flow,affects the solute transport and makes the solute distribution uneven,thus affecting the morphology and the precipitation location of the IMCs.With the increase of the MF intensity,the growth orientation of the IMCs deflects,and the greater the MF intensity,the shorter the deflection time.In addition,with the increase of solidification rate,the plate-like IMCs gradually change into fine structures,and the IMCs are less affected by MF at this time.When a transverse MF is applied during directional solidification,the plate-like IMCs formed at a slow cooling rate transform into dendrite-like structures.The morphology of IMCs is transformed into fine and lamellar structure with the increase of cooling rate.In the slow cooling experiments of bulk solidification,the solute is enriched on one side of the sample due to the flow generated by the transverse MF.The plate-like IMCs forms and grows only on one side of the sample.Further increasing the cooling rate can only refine the IMCs,and the cooling rate plays a dominant role in this process.Fast synchrotron radiation X-ray tomography imaging shows that the transverse MF have a significant effect on the precipitation behavior of IMCs.Melt flow generated by the MF also affects the solute distribution and temperature,resulting in differences in the growth kinetics of IMCs.When the MF is absent,the IMCs firstly nucleate and grow on the oxide layer of the sample,and then precipitate randomly in the center of the sample,while the IMCs only nucleate and grow on the oxide layer of the sample when the MF is applied.The number and volume of IMCs increase sharply at the middle of solidification stage when the MF is absent,and a large number of fine IMCs precipitate in the sample.However,the number and tip growth rate of the IMCs precipitated in the MF are relatively stable.In addition,under the MF,the melt flow transfers the Fe solute from the center to the edge of the sample,which provides sufficient Fe solute for the IMCs to nucleate and grow on the oxide layer of the sample,and eventually the IMCs are formed a ring structure on the surface of the sample.This phenomenon indicates the potential application of MF in the removal of IMCs formed in iron-containing Aluminum alloys.