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In this study, large-sized Al–Zn–Mg–Cu alloy billets were prepared by direct chill casting imposed with annular electromagnetic stirring and intercooling; a process named uniform direct chill casting. The effects of uniform direct chill casting on grain size and the alloying element distribution of the billets were investigated and compared with those of the normal direct chill casting method. The results show that the microstructures were refined and the homogeneity of the alloying elements distribution was greatly improved by imposing the annular electromagnetic stirring and intercooling. In uniform direct chill casting, explosive nucleation can be triggered, originating from the mold wall and dendrite fragments for grain refinement. The effects of electromagnetic stirring on macrosegregation are discussed with consideration of the centrifugal force that drives the movement of melt from the central part towards the upper-periphery part, which could suppress the macrosegregation of alloying elements. The refined grain can reduce the permeability of the melt in the mushy zone that can restrain macrosegregation.

Coarse microstructures and severe macrosegregation always occur in large-sized billets prepared by normal direct chill casting, and cannot be eliminated during subsequent deformation or high temperature annealing. This study proposes a new melt treatment method coupled to annular electromagnetic stirring and intercooling, and applies it to direct chill casting of large-sized 2219 aluminum alloy billets. Compared to the normal direct chill casting, the microstructure and second phase were refined and homogenized, and the macrosegregation of Cu was alleviated. Accordingly, the average tensile and yield strengths, elongation and hardness were significantly improved and remained relatively stable at different positions on the billet. Tensile fracture tests showed that annular electromagnetic stirring coupled with intercooling decreases the amount of porosity in the structure.