The Study On The Effects Of Electromagnetic Fields On The Performance And Organization Of Al-Si Alloy

The ingots of 4045 alloy with diameter of 100mm were processed by Casting Refining Electromagnetic (CREM). Based on the experimental and theoretical analysis of electromagnetic casting analyzes the change of microstructures along with the change of current intensity and frequency. Combining metal solidification theory and magnetohydrodynamis, the effect of electromagnetic field on magnetic force distribution in melts and varieties of flow and temperature field are analyzed, the theory about influence of current intensity and frequency on structures is discussed. The following results were obtained:(1) Combining metal solidification theory and varieties of concentration and temperature field in melts with CREM, come to conclusions: resulting from electromagnetic field, condenser depression augmented, critical grain radius and forming grains energy reduced, nucleate rate increase, which is helpful to forming grain; electromagnetic stirring promotes concentration field to uniform, reduces segregation; electromagnetic stirring also promotes concentration field to uniform, cuts down component-over-cooling, and provides shearing action for dendrite, so it weakens growth condition of dendrite.(2) The quality of ingots is greatly improved by applying the electromagnetic field, which are presented in the following aspects: Firstly, the surface quality is remarkably improved. Casting defects such as scratch marks and exudation are effectively suppressed and the utilization rate of material is raised. Secondly, electromagnetic field make grains finer and homogeneous, and make space between arms of branch-shaped grain shorten. Thirdly, under the conditions of this experiment, the mechanical properties are improved; Tensile strength, elongation and hardness were increased by 16.7%, 22.1% and 11.3%.(3) During the studying on microstructure of 4045 alloy ingot under different electromagnetic frequency and current intensity, this thesis got that not all of the magnetic field can refine grains, and if the condition of the magnetic field is unsuitable, the grain will be thicker than usual one. In the scope of research in this thesis, the ingot has the best microstructure when current intensity is 100A, and the electromagnetic frequency is 20Hz on condition that the pouring temperature is 750℃and the casting speed is 100mm/min,α-Al grains are small and smooth, the mass of them are spherical, Al and Si has the uniform distribution in eutectic area, the eutectic Si is significantly thinned, the organization of the original dendrite area and the eutectic area are uniformly distributed.(4) According to the analysis the effects of frequency on the microstructure of modification alloy, this thesis got the result that the modifier under magnetic field has better result. The effectiveness of improvement differs along with the changes of frequency, the interaction of electromagnetic field and modifier can be used as a new means of grain refinement.