The Effect Of Direct Current On The Solidification Structure Of Eutectic Aluminum Iron Alloy

Solidification refers to the phase transition process from liquid to solid,and the solidification process of metals is essentially the nucleation and growth of grains.Aluminum-iron eutectic alloy has attracted great attention due to its lightweight advantage and excellent mechanical properties such as high hardness,heat resistance,wear resistance,and corrosion resistance.In this study,aluminum iron eutectic alloy was chosen as the research object to achieve non-contact alloy strengthening by introducing direct current during the solidification process.The study focused on aluminum iron eutectic alloy samples with wall thicknesses of 5mm,7.5mm,and 10mm,where direct current ranging from 0 to 30m A/mm~2 was applied.Cooling curves and macroscopic and microscopic microstructures of the aluminum alloy under different current densities were obtained.The effects of current on the macroscopic grain size,microscopic grain growth mode,and eutectic microstructure of the aluminum iron eutectic alloy were investigated.Analyzed the growth mode of macroscopic and microscopic microstructure morphology of aluminum iron eutectic alloy under direct current and its influence on eutectic microstructure morphology;Explored the mechanism of direct current in the solidification process of alloys.Draw the following conclusion:(1)The passage of direct current can refine the grain size andα-Al phase size of aluminum iron eutectic alloy and change the columnar crystal length.As the current density increases,the grain size andα-Al phase size decrease and then increase,the positive columnar crystal increases and then decreases,and the negative columnar crystal decreases and then increases.(2)As the current density increases,direct current affects the undercooling and reheating temperature of aluminum iron eutectic alloy during solidification,first increasing and then decreasing,refining the interlayer spacing of eutectic wafers,and decreasing the proportion of eutectic structure.When the current density is high,the eutectic layer becomes disordered,and even the morphology of the layer cannot be seen clearly.(3)The introduction of direct current can increase the hardness of aluminum iron eutectic alloy samples,As the current density increases,the direct current causes the hardness of the sample to first increase and then decrease.(4)After the metal melt is energized with direct current,the Peltier effect inhibits the formation of nuclei,increases the melt subcooling,and promotes grain refinement,while the Joule effect eliminates various tiny tips on the nucleus surface,promotes nucleation,and reduces the melt subcooling.When the current density reaches a certain value,under the action of the Joule effect,the crystal nucleus tends to become hemispherical,reducing the surface area of the crystal nucleus,promoting the growth of the crystal nucleus,resulting in a phenomenon where the grain size first decreases and then increases with the increase of current density.(5)After the metal melt is energized by direct current,the directional motion of free electrons causes some heat to be brought from the negative terminal to the positive terminal,increasing the cooling capacity of the negative terminal and decreasing the cooling capacity of the melt at the positive terminal,making the length of the columnar crystals near the negative terminal shorter and the length of the columnar crystals near the positive terminal longer.As the current density continues to increase,the free electron movement becomes violent,leading to an increase in the temperature difference between the positive and negative electrodes;the increase in the temperature difference between the positive and negative electrodes leads to more heat transfer from the phonon in the positive region of the alloy to the negative electrode,making the temperature difference between the positive and negative electrodes gradually become smaller.As the current density increases,under the combined effect of these two effects,the positive pole columnar crystal first increases and then decreases,and the negative pole columnar crystal first decreases and then increases.