Zvyšování užitných vlastností vybraných slitin neželezných kovů vícenásobnou plastickou deformaci

Abstract

At present, machine parts used in industry are subject to high demands in terms of their service life at higher loads. It is obvious that in the coming years the area of research and development of such new materials, which would be able to meet these required properties, will be intensively expanded. Furthermore, it is possible to expect an intensive development in the field of processing technologies for conventional materials as a prerequisite for meeting the required application parameters. One of the known methods of increasing the service properties of conventional materials based on steels and non-ferrous metal alloys is forming under conditions of Severe Plastic Deformation (SPD), where the forming process reduces the average grain size and according to known Hall-Petch relationship there theoretically exists a linear dependence between the average grain size and yield strength of polycrystalline materials. It can be predicted that by suitable reduction of the average grain size it is possible to increase the value of the yield strength, or possibly also of other mechanical properties. Particularly large foreign companies from the automotive (load-bearing machine parts) and medical (implants) industries have shown great interest in the method of forming using a high degree of deformation, where research focused on the production of machine parts for critical applications is already underway. The presented dissertation thesis deals with increasing mechanical properties of magnesium alloys AZ61 and AZ80 formed by the method of Equal Channel Angular Pressing (ECAP). The main aim of this work is to study the influence of applied conditions of forming by the ECAP method on the achieved grain refinement of investigated alloys. The influence of the initial state, the geometry of the extrusion tool and the extrusion temperature were analysed with respect to the achieved microstructural changes with a view to increasing the efficiency of the given process. The microstructures of samples formed by the ECAP method under "optimised conditions" were analysed in detail by electron microscopy (TEM, SEM and the EBSD method) to accurately determine the microstructural changes initiated in the formed samples. Further, the influence of SPD on the change of mechanical properties of investigated alloys of small samples was analysed and detailed measurements were performed of hardness distribution according to Vickers (HV) across the sample cross-section.