Recrystallization
of zone-refined aluminium* During the past few years a number of investigators (1,2~3s4) have demonstrated a remarkable decrease in the recrystallization temperature of cold worked aluminium due to the decrease in the impurity content resulting from zone refining. In our experiments we have commenced with a bar of 99.990/ aluminium, 50 cm long and 1 cm2 in cross-section, contained in a graphite boat. A molten zone 3 cm long was maintained using a Radyne highfrequency induction heater whilst the molten zone was traversed at 1 cm/hr. Duplicate bars were prepared after one, two, four and eight passes in this apparatus and the purified sections from each bar were used for the recrystallization studies. Preliminary experiments on materra given eight passes in the zone refining apparatus indicated that recrystallization at room temperature could be obt.ained if the material was given more than 85 per cent cold reduction at room temperature. In consequence, further studies were carried out on material given 40 per cent cold reduction at room temperature. To achieve this, the zone-refined bars were cold-rolled to 0.090 in. sheet, recrystallized at 200ยฐC and finally cold-rolled to 0.054 in. (40 per cent cold work). Samples approximately 3 cm x 1 cm were then annealed for 30 min at various temperatures in the range loo"-320ยฐC. The extent of recrystallization was assessed by an examination under polarized light of electropolished and anodized specimens.