| Electromagnetic casting(EMC) is a new material processing method, a comprehensive subject based on magneto-hydrodynamics(MHD) and combined with metallurgical engineering. The outstanding merits of EMC lie in its high smooth surface, good mechanical properties and high production efficiency, which has become an important method to realize tandem rolling in continuous casting and produce high qualified aluminum alloys. However, the various technological parameters and high control precision require realizing auto-control of EMC in industry. In this thesis, on the one hand, the technical process of EMC is studied to improve the control accuracy of solidification process of ingot, the microstructure and mechanical properties are analyzed to extend the range of application of EMC alloys; on the other hand, the electromagnetic continuous casting (EMCC), which request less control accuracy and is easier to realize industrialization, is proposed and also is applied to practice. The main results are as follows:The electric parameters and induced heating power are calculated using inductance equivalent circuit, the set of equipment of EMC is established; the Al ingot with the cross section size 100x400mm2 is produced and the defects of EMC are analyzed, the preliminary study is made to hot-top EMC.Three type of cooling system fit for EMC are designed, the method of increasing cooling water flux and cooling effect is proposed to improve casting speed of EMC, it is found that the casting speed reached 10.5 cm/min, increased by 30%, using the double-row declining spraying cooling water system.Comparative studies are made to microstructure and mechanical properties of Al round ingots casting by EMC and continuous casting (CC). The EMC ingot has smaller, even microstructure and better mechanical properties; The hardness of EMC specimens increases one times than that of CC ingot and the solution and ageing strengthening properties are better; the abrasion loss of EMC specimen is only 50% of that of CC, that is, the abrasivity of EMC increases one time than that of CC; the EMC ingot has smooth surface and has not interdendritic shrinkage porosity, the precipitation hardening phase more easily forms in EMC, and the fatigue life is three times as high as CC one in as-cast state.A new method of electromagnetic continuous casting, which applied intermediate frequency electromagnetic field in soft-contact mold, is proposed to improve the quality of Al ingot, the shape and fluctuation of liquid surface are measured using low melting alloy in electromagnetic field; the magnetic flux density inside the mold can be improved greatly through slitting in the mold; the amplitude of the fluctuation of the melt surface increase with the reduce of magnetic frequency, thus the stability of the surface decline; the rising height of the surface increase and the surface fluctuation is tempestuous when increasing the magnetic power.In EMCC, the height of the melt surface to the mold top can reach 10mm, however, in EMC, it is less than 2mm, thus, EMCC can be controlled easier; the region of magnetic frequency in EMCC is l-5kHz, which is also larger than in EMC; the grain size is small and even when the frequency is 1kHz, and the ingot has stable liquid column and good surface quality in 5kHz.The defects, such as segregation, lard in ingot surface, can be eliminated through EMCC, consequently the ingot with better surface quality and microstructure is obtained; the Al-l%Si alloy made of EMCC can be used to be the raw material to make Al-Si bonding wire used in integrate circuit; Compared to the common CC ingot, the tensile strength of EMC one increased by 30%, and elongation 70%, which provide a good application in the future.Based on the substitution method of boundary condition, the heat transfer coefficient in continuous casting of aluminum alloy during the process of water cooling is calculated, and a calculation model of heat transfer coefficient is obtained as follows: hw=7.3xl05xW0.77/Ts1.36, which can be used to the numerical...
|
PDF Full Text Request