Study On Industrialized Technology Of Low Frequency Electromagnetic Casting(LFEC) Of Al Alloys

The mutil-ingot low frequency electromagnetic casting (LFEC) process and equipments are successfully developed by introducing LFEC technology into industrial application in this study. Firstly, the effects of technical parameters of casting, hot top and mold structure on the surface quality of7075aluminum alloy LFEC ingots are studied, on the basis of the quality of onsite conventional DC casting ingot. The interference of electromagnetic fields and its effect on microstructure of ingots and distribution of alloy element are focused on during mutil-ingot LFEC process. Also, a new homogenizing aging process is proposed considering microstructural characteristics of LFEC ingots. And then, a set of new process for products has been realized industrialization in Giant Light Metal Technology Co., Ltd and has gained notable economic benefits.The effects of casting speed, quantity of cooling water, overhang size, distance between first and second cooling and the processing method of triangle zone on the surface quality of ingots are systematically studied. The optimum surface of7075aluminum alloy ingot with a diameter of152mm has been achieved as following conditions was obtained that field frequency is15Hz, field current is120A, casting speed is115mm/min, the quantity of cooling water is60L/min, the size of overhang is5mm, the distance from the bottom of the graphite ring to the point when the cooling water contacts ingots is23mm, and the mixture of talc and coconut oil is daubed on the triangle zone.The distribution of magnetic flux density during mutil-ingot LFEC was investigated with finite element simulation and experimental examination. It is found that regardless of current direction, the magnetic field interference among coils appears and the magnetic flux density weakens in the neighbor part of coils. When the current direction of adjacent coils is opposite, the magnetic intensity in ingots is stronger than that of in the same direction. As the distance between coils increases, the magnetic field reduction generated by interference decreases. The magnetic field interference can be alleviated by setting silicon steel sheets or shield, by which the ingot with fine and homogeneous microstructure and uniformly distributed alloying elements can be acquired.The grain is fine and its size is uniform, the amount of non-equilibrium eutectic phases is significantly smaller in LFEC7075Al ingot, compared with that conventional DC casting by a systematical study. However, there is no difference in phases and no change in over-heated temperature between two kinds of ingots.The non equilibrium eutectic phases in LFEC ingots dissolve faster than conventional DC ingots during homogenization. The area fraction of residual phase of LFEC ingot is consistently lower than that of conventional DC ingot after same homogenization. The non equilibrium eutectic phases fully dissolve after three-step homogenization (200℃/2h+460℃/6h+480℃/12h).The deformation resistance of LFEC ingots is lower than that of conventional DC ingots in extruding, so that a sixth of working hours is reduced when an ingot was extruded. The microstructure of the products extruded from LFEC ingots is finer and its average section diameter of grain is about10μm while that of conventional DC extruded bar is20μm.The extruded product from LFEC ingots exhibits better mechanical properties by comparing with DC ingot. Its tensile strength in T6condition is673.50MPa, conductivity is32.4%IACS and it possesses a strong ability of over-aging resistance. It acquires the strength, Vickers-hardness and electrical conductivity676.64MPa,197.88, and35.7%IACS respectively after RRA process (120℃/24h+180℃/30min+120℃/24h).The low frequency electromagnetic mutil-ingot casting technology has been realized industrialization in Giant Light Metal Technology Co., Ltd and its technology has been expanded to produce other superhigh strength Al alloys, such as7050and7459, which has been used to develop a series of new products. Based on statistical results after one-year production, the cost of production decreases about5%and the finished rate increases about20%, the new output value reaches30million RMB, which delivers a direct profit of2million RMB to the company. The developed products have been applied to markets such as high-grade bicycles, electromobile and so on. The industrial practice shows that LFEC technology has brought significant economic benefits.