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The evolution of microstructure, texture, and microtexture in an Al-6 pct Cu-0.4 pct Zr alloy was studied during mechanical testing at 480 ЊC and a strain rate of 5и10 Ϫ4 s Ϫ1 . The as-processed material had an elongated, banded microstructure and a deformation texture with orientation distribution along the ␤-orientation fiber. The true strain vs true stress curve exhibited three stages: I, II, and III. Work hardening occurred in stages I and III, whereas nearly steady-state behavior was observed in stage II. A bimodal distribution of boundary disorientation angles was evident in as-processed material and persisted into stage I, with peaks at 5-15 deg in the low-angle boundary (LAB) regime and at 45-60 deg in the high-angle boundary (HAB) regime. An increase in strain rate sensitivity coefficient, m, in stage I was accompanied by fragmentation of the initial microstructure, leading to the formation of new grains. During stage II the strain rate sensitivity coefficient, m, attained a value of 0.5, which is consistent with the onset of grain boundary sliding. In stage III, the texture and the grain boundary disorientation distribution became randomized while the m value decreased. Grain elongation and cavity formation at second-phase particles and along grain boundaries were seen in samples deformed to failure. The as-processed microstructure is described in terms of deformation banding, and a model for the evolution of such a structure during superplastic deformation is proposed.

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This paper reports the microstructure and creep behaviour of an Al-Cu-Mg-Ti-Ag alloy processed via Osprey forming and extrusion. The microstructure of the as-received extruded bars showed elongated grains towards the extrusion direction, which contained a fine substructure. Elongation to failure values of about 25% were obtained at test temperatures up to 400 • C and for strain rates ranging from 10 −4 to 10 −2 s −1 . In this temperature range, the mechanical behaviour of the alloy was similar to that of particle-strengthened aluminium alloys: (1) the apparent stress exponents of n = 17 and 7 were higher than that reported for most aluminium alloys; (2) the microstructure and the texture did not change significantly during tensile deformation. At temperatures higher than 400 • C, the elongated grains of the microstructure started to recrystallize into smaller grains and a maximum elongation to failure of 170% was observed at 520 • C and 10 −4 s −1 . Tensile tests performed at higher strain rates in this temperature range revealed a stress exponent of 4.5, which corresponds to a slip creep mechanism.