Effect Of Electromagnetic Energy On Fluidity And Microstructure Of A356 Aluminum Alloy

The fluidity of the alloy affects mold-filling capacity and determines whether the alloy can cast complex castings.Its fluidity is closely related to its microstructure,and the solidification process of the alloy has a great influence on its microstructure.Of course the microstructure determines its mechanical properties.In this thesis,A356 aluminum alloy was taken as the research object.A electromagnetic energy grain refinement device independently developed by our group was applied to the solidification process of A356 aluminum alloy above the liquidus temperature to study the influence of electromagnetic energy on the fluidity and microstructure properties of A356 aluminum alloy by setting different electromagnetic parameters.The microstructure of A356 aluminum alloy was observed using metallographic microscopy and scanning electron microscope,the lattice constant and crystal orientation of A356 aluminum alloy were analyzed using XRD,and the change of mechanical properties of A356 aluminum alloy was detected using a universal testing machine and Vickers hardness tester.The experimental results showed that the fluidity of A356 aluminum alloy changed under the action of electromagnetic energy,and the fluidity of the alloy was related to the di/dt and d B/dt of electromagnetic energy.The fluidity of the alloy would increase when di/dt and d B/dt increased,while when di/dt and d B/dt decreased the fluidity of the alloy would decreases.However di/dt and d B/dt were related to electromagnetic parameters.With the increase of frequency,di/dt and d B/dt increased obviously,but they decreased obviously with the increase of duty cycle.Therefore,the fluidity of A356 aluminum alloy increased with increasing frequency and decreased with increasing duty cycle.At the same time,the fluidity of A356 aluminum alloy was also related to the peak current of electromagnetic parameters,and increased with the increase of peak current.In addition,electromagnetic energy was injected into the alloy melt as external energy.By influencing the atoms and atomic clusters,the critical nucleation radius and the nucleation barrier were reduced,and the nucleation rate was increased.Thus,the morphology and size of primary α-Al,eutectic silicon and Fe phase in A356 aluminum alloy were changed obviously.When the frequency was 50 Hz,duty cycle was 0.2 and peak current was 100 A,the average grain size of primaryα-Al was reduced to 27.150 μm at the flow channel,and it was reduced to 43.514 μm at the runner position.The morphology of eutectic silicon was more circular,and its equivalent diameter was 1.220 μm.The Fe phase also became smaller and its size decreased by 39.38%.Electromagnetic energy could improve the tensile properties and hardness of the alloy by refining its microstructure.Based on the experiment results and the theoretical analysis,conclusion could be drawn that electromagnetic energy was helpful to improve the fluidity of A356 aluminum alloy and refine its microstructure.The optimal values of frequency,duty cycle and peak current chosen for solidification process was 50 Hz,0.2 and 100 A.Meanwhile mechanical properties of alloy best at this time...