Influences of Super-Gravity Field on Aluminum Grain Refining

The influence of a super-gravity field on metal grain refining has been mainly investigated using industrial pure aluminum as an example. The relationship between the super-gravity field (gravity coefficient of less than 1000) and the grain size in the equiaxed crystal zone was studied, and the corresponding mechanism for grain refining was discussed in detail. The effect of the super-gravity field on grain refining was remarkable, and the relationship could be well fitted by the second-decreasing-exponential function. For aluminum, the grain size decreased rapidly as the gravity coefficient increased from 1 to 250, and then remained nearly unchanged from 250 to 1000. Under the experimental conditions, the main mechanism was that the fragments of dendritic grains—generated by super-gravity—acted as the nucleation sites and resulted in grain refining. Further, the change of nucleation Gibbs free energy, directly caused by super-gravity, was not remarkable enough to refine the grains, which could be suggested by the stable freezing points under different super-gravity fields.