Basic Research On Microstructure And Properties Control Of Metal Solidification Process Based On Permanent Magnet Stirring

The solidification process from liquid to solid is an important step in the production and preparation of metal materials,and also a key step in the quality control of materials metallurgy,which plays a significant influence on the performance control of metal materials.However,the current mainstream three-phase AC electromagnetic stirrer is faced with high power consumption,high maintenance costs and other problems,which is not conducive to energy-saving and green production.Permanent magnet stirring owns various advantages of simple structure,low energy consumption,low requirements for cooling water,and is an ideal alternative to electromagnetic stirring.However,the research of permanent magnet stirring（PMS）in the solidification process mainly focuses on the solidification microstructure of low melting point alloy,while the research of high melting point alloy and precipitated phase received very little attention.Based on the self-developed permanent magnet stirring device,three alloys with different melting points,namely,tin antimony alloy（lower）,aluminum scandium alloy（medium）and sulfur-containing non-quenched and quenched steel（high）,are selected to investigate the effect of permanent magnet stirring on the structure and properties of metals solidification process.The solidification process of low melting point Sn-11wt%Sb alloy is studied under permanent magnet stirring.It is observed that the melt flow driven by permanent magnet stirring could effectively eliminate the shrinkage holes of Sn-11wt%Sb alloy and refine alloy grains and eutectic microstructure.With the increase of rotating speed from 0 r/min to 180r/min,the longitudinal distribution of precipitated phase Sb₃Sn₄ is significantly improved,and the area proportion difference between the upper and lower regions of Sn-11wt%Sb alloy decreases from 17.05%to0.41%.The average friction coefficient of Sn-11wt%Sb alloy decreases from 0.77 to 0.72,and the wear surface width decreases from 1.51 mm to0.81 mm.The solidification process of medium melting point Al-2wt%Sc alloy is studied under permanent magnet stirring.The results revel that gravity segregation of Al₃Sc in Al-2wt%Sc alloy is significantly improved with the increase of rotating speed from 0 r/min to 150 r/min,and the difference of the area proportion of primary phase in upper and lower regions decreased from 44.36%to 0.73%.The microhardness test shows that the microhardness of Al₃Sc phase is 172.9 HV,which is much higher than that of the matrix 28.6 HV.Due to the uniform distribution of Al₃Sc phase with high hardness,the macroscopic Brinell hardness of Al-2wt%Sc alloy increases from 20.9 HB to 27.8 HB,and the tensile strength increases from80.9 MPa to 128.2 MPa.The solidification process of high melting point 49Mn VS3 steel is studied under permanent magnet stirring.It is found that the precipitation of Mn S along grain boundaries is inhibited and the distribution is more uniform with the increase of rotating speed from 0 r/min to 150 r/min.The number of Mn S increases from 1440 n/mm² to 2335 n/mm²,and the average size of Mn S decreases from 7.2μm to 3.2μm.The content of intragranular ferrite increases from 0.3%to 3.1%,and the proportion of intragranular ferrite to the total ferrite increases from 2.6%to 25.2%.The tensile strength of the steel is enhanced from 605.8 MPa to 689.4 MPa,and the elongation is enhanced from 7.5%to 8.9%.Permanent magnet stirring can refine the size of Mn S,increase the number of Mn S,promote the uniform distribution of Mn S,and thus promote the formation of ferrite in grain,and improve the tensile properties of steel.