| In the past hundred years,China has made great efforts in the research and development of aluminum alloys.In the early days of the founding of the People’s Republic of China,in order to build and improve the formed aviation technology as soon as possible,the country made great efforts to develop the aluminum alloy industry and broke through the barriers of alloy technology restrictions.The development was particularly rapid,and the scope of use continued to expand.Up to now,China has also made remarkable achievements in metal materials,non-ferrous metals and other fields.However,in order to make the alloy have more perfect performance,technical innovation is also urgent.The new technology of external electromagnetic field is favored because the electromagnetic force generated by it is pollution-free and does not directly act on the alloy melt to refine the melt structure and control its solidification forming process,which provides a broader development space for preparing alloys with excellent mechanical properties.Therefore,this thesis aims to solve the problems of the cutting damage of coarse and irregular primary Si in the solidification structure of Al-7%Si alloy,and the internal porosity,shrinkage cavity,porosity and solute inequality of Al-7%Si alloy.The effects of electromagnetic field and induction coil coupling on the solidification structure and properties of Al-7%Si alloy were systematically studied.Firstly,the former electromagnetic stirring technology has been improved.Two kinds of electrodes are set: double electrodes and coaxial electrodes are inserted into the alloy liquid surface to perform electromagnetic stirring on the solidified structure of Al-7%Si alloy.The results show that proper current can indeed strengthen the internal structure of the alloy,homogenize the structure,reduce the undercooling and the internal and external temperature gradient,avoid the secondary crystallization of the alloy crystal,eliminate the directivity of the alloy solidification,and cause the columnar crystal to gradually reduce to equiaxed crystal.The heat preservation effect on the alloy can make the current fully stirred,so that the stirring effect can be applied to the early solidification stage,further refine the alloy structure,and increase the α-The compactness between Al phase and primary Si can also reduce defects such as bubbles and cracks.However,if the heat preservation is carried out under excessive current,more irregular turbulence will be generated in the alloy liquid.During the solidification and contraction of the alloy,the turbulence will cross the lattice to destroy the internal structure of the alloy,leading to the failure of the alloy product performance.On this basis,two kinds of nano particles were added into the alloy to study the strengthening of the relative alloy structure.And the dispersion distribution of nano particle reinforced phase in the alloy under the action of electrode.The analysis shows that when the power is off,the particle cluster shape is large,and a large number of particles will fall off near the dispersed silicon phase due to insufficient adhesion,which will accelerate the growth of holes and cracks.After the current is applied,not only the adhesion of nanoparticles is increased,but also the directivity of particle clusters can be eliminated by the agitation of the flow field.Large area of pins are pinned on the grain boundary,which hinders the Directional growth of α-Al phase.The purpose of grain refinement is achieved,and the mechanical properties of the alloy are enhanced.In addition,the effects of the two electrodes in the experimental scheme on the internal flow field of the alloy were simulated respectively,and two turbulence models(SST and LES)were used to analyze the dispersion of particles in the alloy.It was believed that particles would be affected by turbulence clusters of different sizes according to the current intensity under the large eddy simulation,and the turbulence simulation results were closer to the experimental items. |
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