The superplastic deformation process is interesting not only from the scientific point of view but also because of benefits it offers when applied in industry. The generation of superplastic structures in aluminium alloys of the 7XXX type depends on the formation of precipitates in suitable amount, size and dispersion which may be obtained by thermomechanical treatment. The A7475 alloy was continuously cast, extruded and thermomechanically treated. The investigations on creating precipitates and microstructure of the AIZnCuMgCr alloy were performed using optical, scanning and transmission electron microscopy and X-ray phase analysis. The morphology of the alloy after a full thermomechanical treatment showed fine, equiaxial average grain about 12 urn in size. The strain rate sensitivity coefficient m determined from tensile tests was estimated between 0.56-0.70. About 495 pct elongation was obtained in a tension test at the flow stress of 3 MPa, strain rate 8 x I O 3s I and temperature 790 K. It demonstrates that material of good superplastic properties was elaborated.

The suitable structure of an alloy affects its superplastic properties due to a basic mechanisms of superplastic deformation. A fine structure of equiaxial grains appears in the alloy provided there are dispersoids and intermetallic compounds of certain size and distribution. The composition of the 2:XXX - type alloy (with Ni - addition) as well as a special thermomechanical treatment allowed to obtain a suitable structure of 15 μm-grain size and an equiaxial shape. The formation of such microstructure was investigated using optical, scanning and electron microscopy, as well as X-ray phase analysis techniques. The X-ray and electron microscopy with EDAX analyser allowed to determine the type and morphology of the intermetallic compounds, very important to generation the fine-grained structure. The superplastic state regarding quality of the structure was verified in tensile tests performed at the range of deformation rates between 1.4 x 10--4 to 7 x 10-3 s-1 and at temperatures from 789 K to 839 K, which allowed to attain the elongation above 300% and strain rate sensitivity coefficient m = 0.509.

Fine equiaxial grain structure is a consequence of designing a material with a large contribution of intermetallic compounds of certain size and distribution. A 2XXX alloy with Fe, Ni, Mn and Zr additions was cast obtaining large amounts of Al-Fe-Ni and Al-Cu-Mg precipitates, in which the Al-Zr compounds appeared as dispersoids. After the application of a modified thermomechanical procedure, an alloy with average grain size of 12 μm with a large contribution of grains smaller than IO μm has been obtained. Apart from that, elongated precipitates of0.8-4.0 μmin size as well as globular ones about 0.3 urn large were produced in the alloy after recrystallization. The alloy revealed high resistance to grain growth at high temperatures, which was due to the appearance of intermetallic compounds (mostly Al-Fe-Ni) in grain boundaries.