7050 aluminum alloy ingots with 162 mm in diameter were prepared by direct chill（DC） casting process with applying a low frequency electromagnetic field

and effects of electromagnetic field on the as-cast microstructure were investigated.The experimental results show that low frequency electromagnetic field has a significant effect on both grain size and morphology of grains in 7050 alloy.The average grain size is evidently reduced from 230 μm to about 42 μm

and the morphology is transformed from coarse dendrite to fine spherical euiaxed structure.The electromagnetic field frequency and intensity play very important roles in refining the grain size.The optimum processing parameters for casting 7050 alloy ingot with 162 mm are presented as follows:electromagnetic field frequency of 25 Hz and electromagnetic field intensity of 12 800～16 000 At.