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The microstructure and its evolution during isochronal annealing of a twin roll cast Al-3.2Mg-0.19Sc-0.14Zr (wt.%) alloy was investigated by light optical microscopy and electron microscopy. Two procedures - equal channel an- gular pressing and annealing at 300 řC for 8 h were applied to enhance mechanical properties of the alloy. The annealing led to the precipitation of a fine dispersion of Al3(Sc,Zr) particles providing an increase of ∼20 HV in the Vickers microhard- ness. Equal channel angular pressing refined significantly the microstructure and raised the microhardness by about 30 HV. Applying of the 300 řC / 8 h both before and after equal channel angular pressing did not induce further strength- ening. However, the precipitation of the Al3(Sc,Zr) phase had a stabilizing effect when the material was exposed to the subsequent isochronal annealing. 1

Mechanical properties of aluminium alloys highly depend on their phase composition and microstructure. High strength can be achieved among others by introduction of a high volume fraction of fine, homogeneously distributed second phase particles and by a refinement of the grain size. Powder metallurgy allows to prepare fine grained materials with increased solid solubility which are favourable precursors for further precipitation strengthening. Gas atomization was used for the preparation of powders of the commercial Al7075 alloy and its modification containing 1 wt% Zr. A part of gas atomized powders was mechanically milled at different conditions. Mechanical milling reduced the grain size down to the nano-size range and the corresponding microhardness exceeded the value of 300 HV. Powders were consolidated by the spark plasma sintering method to nearly fully dense compacts. Due to a short time and relatively low temperature of sintering the favourable microstructure can be preserved in the bulk material. The grain size of compacts prepared from milled powder was retained in the submicrocrystalline range and the microhardness close to 200 HV exceeded that of the specially heat treated ingot metallurgical counterparts. The prepared compacts retained their fine grained structure and high...

Mechanical properties of ultra-fine grain magnesium alloys AE42 and LAE442 prepared by ECAP were investigated. The study was focused on finding suitable conditions for the superplastic deformation. In the first place, the thermal stability of the microstructure was investigated. Afterwards, the strain rate sensitivity was measured in the temperature range 180-240 řC and the strain rate of =5·10-5 -2·10-3 s-1 . Conditions for tensile tests of =10-4 s-1 at 180 ř C and =10-3 s-1 at 240 řC ware selected. Finally, the microstructure change as a result of deformation was observed by AFM and EBSD. The results were discussed with mechanical tests. The best superplastic properties were observed in LAE442 alloy deformed at 180 ř C and =10-4 s-1 . Under these conditions, the achieved tensile strain was 395%.