Nanostructured Al-3.0Fe-0.42Cu-0.37Mn powder alloy was deformed by extrusion over a temperature range of 375C to 425C, a ram speed range of 1 to 30 mm/s, and an extrusion rate of 10:1. Flow stresses and strain rates were calculated from the experimental ram pressures and speeds. The stress–strain-rate–temperature relationship in the extrusion of the nanostructured alloy was found to be similar to that in hot-worked conventional materials. The extrusion, torsion, compression, and creep data of nanostructured and conventional materials, extending over ten orders of magnitude of strain rate and over two orders of magnitude of stress, were correlated by a hyperbolic-sine constitutive equation, because the power and exponential laws lose linearity at high and low stresses, respectively. The hyperbolic-sine equation was widely used to correlate the hot-working behavior of conventional materials. It was concluded that the hot working of nanostructured powders was a thermally activated process in which the rate-controlling mechanism was the climb of edge dislocations. Microstructural changes in the consolidated alloys as a function of the extrusion conditions were investigated. An analysis was made of the dislocation behavior in very small grains of nanostructured metal by transmission electron microscopy and a dislocation structure and the different ways it appears in 40 to 100nm Al-alloy grains was identified. Also discussed were the thermally activated propagation of dislocations and their interactions with shear bands/grain boundaries, and dislocation loops. Microstructural features including low-angle grain boundaries, high-angle grain boundaries, and equilibrium grain boundaries and sub-grain boundaries were observed. Dislocation structures under deformation conditions were studied to investigate the microstructural evolutions, which revealed some unique microstructural features such as dislocation tangle zones and dense-dislocation walls, and the recovery process was discussed herein.

Effect of Dislocation Mechanisms during Extrusion of Nanostructured Aluminum Powder Alloy. A.M.Jorge, M.M.Peres, C.S.Kiminami, C.Bolfarini, W.J.Botta: Metallurgical and Materials Transactions A, 2009, 40[13], 3322-30