The paper presents results of FEM modelling as well as properties and microstructure of the ultralow-carbon ferritic steel after the unconventional SPD process—DRECE (dual rolls equal channel extrusion). Based on the conducted numerical simulation information about the deformation behaviour of a steel strip during the DRECE process was obtained. The simulation results were experimentally verified. The influence of DRECE process on hardness distribution, fracture behaviour and microstructure evolution of the investigated steel was analysed. The increase of steel strength properties after subsequent deformation passes was confirmed. The microstructural investigations revealed that the processed strips exhibit the dislocation cell microstructure and subgrains with mostly low-angle grain boundaries. The grains after processing had relatively high dislocation density and intense microband formation was observed. It was also proved that this unconventional SPD method fosters high grain refinement.

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A growing interest in wrought magnesium alloys has been noticed recently, mainly due to development of various SPD (severe plastic deformation) methods that enable significant refinement of the microstructure and -as a result -improvement of various functional properties of products. However, forming as-cast magnesium alloys with the increased aluminum content at room temperature is almost impossible. Therefore, application of heat treatment before forming or forming at elevated temperature is recommended for these alloys. The paper presents the influence of selected heat treatment conditions on the microstructure and the mechanical properties of the as-cast AZ91 alloy. Deformation behaviour of the as-cast AZ61 alloy at elevated temperatures was analysed as well. The microstructure analysis was performed by means of both light microscopy and SEM. The latter one was used also for fracture analysis. Moreover, the effect of chemical composition modification by lithium addition on the microstructure of the AZ31-based alloy is presented. The test results can be helpful in preparation of the magnesium-aluminum alloys for further processing by means of SPD methods.

Hot compression tests of the AZ31 magnesium alloy, performed for wide ranges of temperature and strain rate, revealed two different flow curve types for the material investigated. At higher strain rates and lower temperatures, flow curves exhibit a distinct peak. At lower strain rates and higher temperatures, flow stress values change less rapidly. This makes it difficult to find a single function able to accurately describe the deformation behaviour of AZ31 alloy in the entire forming range.The present study discusses an effect of the AZ31 magnesium alloy flow stress description on the accuracy of extrusion force prediction by means of FE simulation. A number of forward extrusion trials were carried out in order to acquire experimental data on AZ31 alloy deformation behavior in various forming conditions. Cylindrical billets of 40 mm in diameter and the tooling were initially heated to temperatures in the range of 200 to 400• C and placed in the working space of the 1500 kN hydraulic press to produce extruded rods of 12 mm in diameter. Numerical models for conducting corresponding extrusion simulations were prepared in Forge 2009 software and the selected form of Hensel-Spittel function was applied for the material flow stress description. Function coefficients were calculated both for the entire forming range of AZ31 alloy as well as for the ranges of parameters specific to a certain extrusion trial conditions. The numerical results were compared to the experimental ones and the accuracy of both approaches were estimated. It was found that the selected flow stress function, determined for the wide ranges of temperature and strain rate, allows to achieves a tis factory accuracy of AZ31 alloy extrusion force prediction by FE simulations.Keywords: magnesium alloy, AZ31, flow stress, extrusion, FE simulation Dwa różne rodzaje krzywych płynięcia uzyskano w próbach ściskania na gorąco stopu magnezu AZ31, prowadzonych dla szerokiego zakresu temperatury i prędkości odkształcenia. Dla wyższych prędkości odkształcenia i niższych temperatur krzywe płynięcia wykazują wyraźne maksimum naprężenia uplastyczniającego. Dla niższych prędkości odkształcenia i wyższych temperatur zmiany wartości naprężenia uplastyczniającego są mniej gwałtowne. Z tego względu trudno jest znaleźć jedną funkcję opisującą zależność naprężenia uplastyczniającego dla całego zakresu warunków odkształcania stopu magnezu AZ31.W artykule przedstawiono wpływ zastosowanej funkcji naprężenia uplastyczniającego stopu AZ31 na dokładność wyznaczania siły wyciskania poprzez symulacje MES. Przeprowadzono szereg prób wyciskania współbieżnego w celu uzyskania danych doświadczalnych charakteryzujących zachowanie się stopu AZ31 w różnych warunkach kształtowania. Próbki walcowe o średnicy 40mm wraz z przyrządem do wyciskania były nagrzewane do temperatury w zakresie od 200 do 400• C i umieszczane w przestrzeni roboczej pionowej prasy hydraulicznej o nacisku 1500kN. Następnie wyciskano z nich pręty o średnicy 12mm. Próby wyciskania zostały zamodelowane w programie FORG...