Improvement of press formability of aluminium sheets

Abstract

The effects of cold reduction before annealing and final annealing conditions on the r and n values, press formability, and textures of commercially pure aluminium sheets and the correlation among these properties have been investigated. Cold reduction before annealing strongly affects r values of fully recrystallized sheets: r ₄₅ and r markedly increased with increasing cold reduction (> 90%), and the order of r value with test direction changed owing to recrystallization. Two regions can be distinguished: in the first (50 to about 84% reduction), the order of r value is changed from r ₄₅> r ₉₀>r ₀ to r ₉₀ r ₀ r ₄₅, whereas in the second (reductions >90%),r ₄₅ >r ₉₀ >r ₀ is changed to r ₄₅ > r ₀≳r ₉₀. For sheets cold rolled to 90% and larger reductions, r ₄₅ and r show high peak values, and good drawability is gained at partial recrystallization. The variation in r value with increasing annealing temperature and its variation with cold reduction before annealing can be qualitatively correlated with that of texture. In order to improve the press formability, it is essential that aluminium sheets be cold rolled with as great a reduction as possible (> 90%) and then fully annealed.