Papers by Author: L.L. Rokhlin

Abstract: Severe plastic deformation of a Mg-Al-Ca alloy resulted in different types of grain structure. High pressure torsion (HPT) was shown to lead to the formation of a nanocrystalline structure with a grain size of 100-200 nm, while equal channel angular pressing (ECAP) produced ultrafine grained (UFG) or submicrocrystalline (SMC) structures, depending on the ECAP temperature. An UFG structure with a grain size of 2-5 -m was formed at 300°C, as distinct from a finer SMC structure with a grain size of 300-800 nm formed at a lower temperature (220°C). The possibility of increasing the strength of the alloy in the UFG condition by a factor of 1.5-2, combined with a reasonable level of ductility and enhanced functional properties was thus demonstrated. ECAP of annealed Mg-Al-Ca with the formation of UFG structure was shown to lead to increased yield strength (by a factor of 2) and enhanced tensile ductility (by a factor of 3).

Abstract: Texture and microstructure formation during equal channel angular pressing (ECAP) of Mg-0.49%Al-0.47%Ca alloy were studied. The selected ECAP condition (route BC, N=6 passes, true strain ε ≈ 6.8, T=300°C) ensures an ultrafine-grained structure of the alloy and basal texture, inclined at an angle of 45-55º relative to the direction of extrusion. The expectation that such a change of the texture, together with the refinement of microstructure, should improve the low temperature ductility of this material was confirmed by tensile testing.

Abstract: In this work severe plastic deformation (SPD) was applied to magnesium base alloys of the Mg-Sm system (2.8-5.5 mass %Sm). These alloys are characterized by high strength at elevated temperatures and high strengthening effect during aging. SPD was performed by torsion under pressure of 4 GPa at 20 and 200°C to ε ∼ 6. SPD results in significant strengthening of the Mg-Sm alloys due to the formation of submicrocrystalline structure. In all cases SPD accelerates the solid solution decomposition upon subsequent aging. The highest strengthening can be obtained if the solution treated alloy is aged at 200°C after SPD at room temperature. The state of high strength can be also reached if the following sequence of the operations is used: solution treatment + aging at 200 °C up to maximum hardness + SPD at 20°C + aging at 200°C accompanied by Sm –rich phase precipitation in the submicrocrystalline matrix.

Abstract: The effect of the supersaturated solid solution decomposition occurring prior to, during, and after severe plastic deformation by torsion under high hydrostatic pressure on strengthening is examined by the examples of Al-Cu-Mg, Al-Mg-Sc, and Mg-Sm alloys and 0.12%C-0.85%Mn- 0.65%Si and 0,1%C-1.12%Mn-0.08%V-0.07%Ti low-carbon steels. The decomposition of the supersaturated solid solution was realized upon cooling from the quenching temperature (lowcarbon steels), prior to deformation (Al-Cu-Mg-, Mg-Sm alloys), during deformation (Al-Cu-Mg-, Mg-Sm alloys), and after deformation. It is shown, the decomposition of the supersaturated solid solution is effective for the grain refinement down to nanoscale and strengthening, but, for different materials, different combinations with SPD should be used.