Research On Soft-contact Electromagnetic Continuous Casting Technology Of Ultra High Strength Aluminium Alloy Slabs

7050 and 7055 ultra high strength aluminum alloys,which have the advantages of low density,high specific strength and good hot-workability,are used as principal structural materials in aerospace field due to their excellent properties of thermal and electrical condutivities and corrosion resistance.However,cracks and element segregation exist in conventional semi-continuous casting due to complex alloy components,which badly affect the yield and mechanical properties.So soft-contact electromagnetic continuous casting technology of ultra high strength aluminum alloy slabs is researched in this paper.The mould is a key equipment of soft-contact electromagnetic continuous casting technology.In this paper,the optimal design of electromagnetic structure in the mould shows that magnetoresistance of magnetic circuit is reduced by reasonably putting the silicon-steel sheets with good magnetic conductivity around the inductive coils,which optimizes the distribution of magnetic field in the mould.The best positions of silicon-steel sheets located in the mould are as following:the silicon-steel sheets are located in both the bottom and side of the coils,6 silicon-steel sheets with the thickness of 1.8 mm are located in the side of coils, which distances 8.5 mm from the coils.The optimized distributions of magnetic field in the mould are as follows:magnetic intensities at the same height plane of mould are strongest in the corner,weaker at the center of short side,which is higher than that of the center of long side,weakest at the center of the plane;the value of magnetic intensity is biggest in the half height of the inductive coils.The magnetic intensities without loading are higher in the middle plane of coils,lower in the upper surface of the coils.The magnetic intensity is bigger in middle plane of the coils when loading in the coils and the distribution of magnetic field is more uniform,which is beneficial to the soft-contact electromagnetic continuous casting.According to experiments,the device of soft-contact electromagnetic continuous casting has been improved.The effects of casting parameters on the ultra high strength aluminum alloy slabs have been studied.The results show that when the current intensity is 50A, electromagnetic frequency is 800 Hz,casting temperature range is 698-704℃,casting speed is 65 mm/min,the flow of cooling water is 2-3-4 m~3/h and liquid level is at the half height of the graphite mould,we can produce 7050 and 7055 slabs with the seize of 430mm×120mm×850mm successfully through pure aluminium pedestal and slow cooling technologies,the slabs have smooth surfaces without cracks,cold traps,melting,segregation defects such as tumors.The structure analysis results of the slab indicate that the above method can effectively refine microstructure and refrain element macro-segregation.The average grain size is reduced from 71.4μm to 62.9μm in 7050 slab and from 57.50μm to 47.31μm in 7055 slab with the application of electromagnetic field.The analysis results of cracks and properties of the slab show that mechanical properties are increased by soft-contact electromagnetic continuous casting technology,the tensile strength and elongation of 7050 slab are increased by 6.21%and by 23.49%respectively,compared to those without electromagnetic field.The potential causes of cracks are eliminated and the yield of slabs is increased a lot.