Study On Microstructure And Properties Of Spiral Self-inoculation Al-Si Alloy Ingots

Accurate control of casting solidification process can not only improve the quality of the ingot,but also obtain the necessary structure and properties,which has an important influence on solidification casting.The grain refinement technology,the most commonly used in solidification control,is constantly innovating.Refined grains,less segregated and higher-mechanical properties of ingots can be obtained by grain refinement.The sodium thiosulfate was used for simulating the solidification process of the spiral self-inoculation in this paper;The optimum electromagnetic stirring parameters were obtained by ANSYS-Fluent software,which was used to simulate the solidification process of the metal under the electromagnetic stirring;The solidification process of Al alloy was obtained in situ by applying magnetic field and inoculation treatment with confocal scanning laser microscopy;The solidification optimization experiments of Al alloy ingots were carried out by using the data obtained from the experiments and simulation.The result is as follows:（1）Sodium thiosulfate melts with reduced superheat,accelerated solidification rate,heterogeneous nucleation rate increased by melt and refined solidification structure can be obtained by the treatment of the sodium thiosulfate spiral self-inoculation.The electromagnetic field is distributed symmetrically in radical direction and attenuates from the surface to the center of the ingot the size isΦ0.1m×0.1m calculated by ANSYS-Fluent software.When the frequency is constant,the magnitude of magnetic induction and electromagnetic force is directly proportional to the current intensity.When the current is constant,with the increase of the frequency,the electromagnetic force increases.With the increase of frequency,within the radius of 0 to 0.04m,the magnetic induction decreases,but when the radius is within 0.04m to 0.05m,the magnetic induction increases.The distribution of velocity is that increases first and then decreases from the center to the surface.The location of the maximum velocity and the minimum velocity of the melt flow is on the radius value of 0.04m and the center,respectively.The velocity of melt flow increases obviously,when the frequency increases from 10Hz to 20Hz,and changes little and almost uniformly,when the frequency increases from 20Hz to 30Hz.The melt temperature reduces faster and the solidification speed increases under electromagnetic stirring.（2）In-situ observation by CSLM shows that the final microstructure of the ingot is significantly reduced after the application of magnetic field and self-inoculation treatment.The spacing is significantly reduced of the Al₂Cu structure precipitates from the boundary,which the shape is mainly lamellar and the size is small.The hardness of the alloy is obviously improved.From the solidification experiment of Al-Si alloy ingot,it can be concluded that the synergistic effect of the electromagnetic stirring and the self-inoculation process can significantly refine the grain structure and improve the segregation of the ingot.Under the effect of electromagnetic stirring,the morphology of theα+Si phase of the boundary precipitate changes from the original acicular shape to the lath shape,and the length is reduced.The grain structure under the electromagnetic stirring and self-inoculation treatment process is further reduced,the distribution of the precipitated phase is more uniform,and the precipitated morphology becomes a plate-like shape,and the length is further reduced.The average grain size is 209μm,176μm and 164μm.The average size of the precipitatedα+Si phase is 59.65μm,28.55μm and 24.04μm,respectively.