Grain Control in Aluminium

Abstract

The methods by which grain control is achieved in the commercial production of rolled aluminium are reviewed. A summary of the recognized mechanisms of nucleation and recrystallization observed in aluminium and its alloys is given, followed by consideration of the way in which the various stages of fabrication, from casting to final annealing, may be used to control grain structure. While in certain circumstances alloying additions that remain in solution throughout processing can lower the recrystallization temperature of aluminium, alloying additions more generally raise the recrystallization temperature. The semi-continuous casting process results in a supersaturated matrix containing a dispersion of cast intermetallic particles. The coarse particles, also widely spaced, accelerate recrystallization, while fine-scale precipitation from supersaturated solid solution exerts important influences upon recrystallization temperature, grain shape, and preferred orientation. As several of the commonly occurring alloying additions have low solubility and low rates of diffusion, considerable control can be achieved over the stage at which fine-scale precipitation occurs to achieve the maximum effect.