Ultrafine grain and nanocrystalline materials show attractive properties - very high strength and relatively good ductility. Such metals can be produced by severe plastic deformation methods. In the previous work , it was shown that the hydrostatic extrusion results in grain refinement to nanometer scale of aluminium alloys. This processing method can be used to produce large fully-dense bulk elements (rods of various cross-section shapes and lengths much higher than in other techniques). The aim of this work was to show how the properties of nano-sized age hardenable aluminium alloy depend on the initial microstructure (single or two-phase) of extruded samples.
The material used in this study was an Al-4Cu-1Mn-0,5Mg aluminium alloy. In the as-received state, the material had a form of 20 mm diameter rod. The specimens were solution heat treated, water quenched and some of them aged at various conditions. Next, they were subjected to the hydrostatic extrusion under high pressure. The final diameter was 3 mm which corresponds to the cumulated true strain of 3,67. In order to characterize the mechanical properties of the materials, microhardness measurements and tensile tests were performed.
The results have shown that the highest strength is achieved for the specimen deformed in the as quenched condition. Moreover, this sample exhibits the highest value of elongation during tensile deformation. These results will be discussed in terms of microstructure evolution during severe plastic deformation (grain refinement rate, precipitates transformation).
 M. Lewandowska, H.Garbacz, W. Pachla, A. Mazur, K.J. Kurzydłowski: „Hydrostatic Extrusion and Nanostructure Formation in an Aluminium Alloy" Solid State Phenomena, in press.