Effects of low frequency electromagnetic casting on solidification macrostructure of GH4742 superalloy

The low frequency electromagnetic casting (LFEC) was used to prevent hot cracking during the solidification process of GH4742 superalloy ingot. The effects of LFEC on the solidification macrostructure of the ingot were investigated through experiments and simulation. The results show that the average grain size decreases after application of LFEC. At the same time, the fraction of equiaxed grains increases compared with the ingots that without LFEC. In addition, the average grain size decreases and the fraction of equiaxed grains increases with increasing the current frequency. When the current frequency increases from 5 Hz to 20 Hz, the average grain size decreases from 5.39 mm to 4.74 mm, and the fraction of equiaxed grains increases from 41.21% to 55.24%. The distribution of Lorentz force, melt flow field and temperature field in the melt was simulated using COMSOL Multiphysics software. It is found that the Lorentz force increases and the forced convection is enhanced with increasing the current frequency, thus the melt flow velocity and heat transfer in the melt are promoted. It can facilitate the heterogenous nucleation in the melt, resulting in grain refinement, and further preventing hot cracking of large size ingots.