The Effects of Processing Variables on Formability of Aluminium Sheets : 2nd Report, The Effect of Annealing Temperature

Abstract

The optimum processing conditions of commercially pure aluminium sheet for the pressformability are clarified in correlation with the tensile properties, crystallographic orientation and microscopic structure, by testing sheets differently cold-reduced and annealed at various temperatures. It is concluded that the drawability is governed by the minimum value of r in the sheet plane, similarly to the case of the as-rolled sheets in the previous report. Therefore, the processing conditions which increase the minimum value of r are effective in improving the drawability. The r-value of the tensile specimen taken at 0° to the rolling direction is minimum in the asrolled sheets, but the r-value at 45° becomes minimum in the fully annealed sheets. The numerical order of the r-values in the three directions is in most cases reversed by annealing. The minimum value of r becomes largest at the transition point of this reversal, where recrystallized grains are partially observed. In addition, at this point, the earless condition is satisfied. The heavier the cold reduction prior to annealing the higher becomes the minimum value of r.