THE INFLUENCE OF CASTING PRACTICE ON THE CRITICAL STRAIN AND SUBSEQUENT GRAIN-GROWTH OF COMMERCIAL PURITY ALUMINUM

The dependence of critical strain and subsequent selective abnormal growth of large grains in commercial purity aluminium containing 0.5 wt.% Fe on ingot structures has been studied. Wedge-shaped strain-annealed specimens taken from sand-cast and direct-chill-cast slabs were cold rolled which gave a strain gradient ranging from 0 to 25%, and after annealing at selected temperatures for 1 h the structures were assessed. The current work also investigated the effects that heat treatment (homogenization) and other processing variables might have on critical strain and maximum grain size values. It has been shown that a satisfactory final structure can result from widely differing cast structures (casting operations) by appropriate combinations of the operational variables; provided that the characteristics of deformation and annealing are controlled it is possible to avoid the occurrence of abnormal or critical grain growth in the processed products.