The magnesium AZ31 alloy was swaged with rotary pressure with the aim of redefining the microstructure and improving mechanical and fatigue properties. The rotary swaging process and subsequent ageing improved the yield stress in tension and compression. In the present study, the investigation was focused on fatigue behaviour. The samples were cycled in a symmetric regime with a frequency of 35 Hz. A dependence of the stress amplitude on the number of cycles up to the fracture was estimated. The microstructure of the samples and fracture surfaces was analysed with a scanning electron microscope. The fatigue process was influenced by the pronounced texture formed in the swaging process. The fatigue properties of the swaged samples improved substantially-the endurance limit based on 107 cycles was approximately 120 MPa-compared to those of the cast alloy. The analysis of the fracture surfaces showed a transcrystalline fatigue fracture.

• Klíčová slova
• fatigue life, fractography, magnesium alloy AZ31, non-basal slip, rotary swaging, twinning,
• Publikační typ
• časopisecké články MeSH

An extruded magnesium AZ31 magnesium alloy was processed by rotary swaging (RSW) and then deformed by tension and compression at room temperature. The work-hardening behaviour of 1-5 times swaged samples was analysed using Kocks-Mecking plots. Accumulation of dislocations on dislocation obstacles and twin boundaries is the deciding factor for the strain hardening. Profuse twinning in compression seems to be the reason for the higher hardening observed during compression. The main softening mechanism is apparently the cross-slip between the pyramidal planes of the second and first order. A massive twinning observed at the deformation beginning influences the Hall-Petch parameters.

• Klíčová slova
• dislocation density, grain size, magnesium alloy AZ31, residual stresses, strain hardening, twinning,
• Publikační typ
• časopisecké články MeSH

UNLABELLED: The application of biodegradable magnesium-based materials in the biomedical field is highly restricted by their low fatigue strength and high corrosion rate in biological environments. Herein, we treated the surface of a biocompatible magnesium alloy AZ31 by severe shot peening in order to evaluate the potential of surface grain refinement to enhance this alloy's functionality in a biological environment. The AZ31 samples were studied in terms of micro/nanostructural, mechanical, and chemical characteristics in addition to cytocompatibility properties. The evolution of surface grain structure and surface morphology were investigated using optical, scanning and transmission electron microscopy. Surface roughness, wettability, and chemical composition, as well as in depth-microhardness and residual stress distribution, fatigue behaviour and corrosion resistance were investigated. Cytocompatibility tests with osteoblasts (bone forming cells) were performed using sample extracts. The results revealed for the first time that severe shot peening can significantly enhance mechanical properties of AZ31 without causing adverse effects on the growth of surrounding osteoblasts. The corrosion behavior, on the other hand, was not improved; nevertheless, removing the rough surface layer with a high density of crystallographic lattice defects, without removing the entire nanocrystallized layer, provided a good potential for improving corrosion characteristics after severe shot peening and thus, this method should be studied for a wide range of orthopedic applications in which biodegradable magnesium is used. STATEMENT OF SIGNIFICANCE: A major challenge for most commonly used metals for bio-implants is their non-biodegradability that necessitates revision surgery for implant retrieval when used as fixation plates, screws, etc. Magnesium is reported among the most biocompatible metals that resorb over time without adverse tissue reactions and is indispensable for many biochemical processes in human body. However, fast and uncontrolled degradation of magnesium alloys in the physiological environment in addition to their inadequate mechanical properties especially under repeated loading have limited their application in the biomedical field. The present study providesdata on the effect of a relatively simple surface nanocrystallziation method with high potential to tailor the mechanical and chemical behavior of magnesium based material while maintaining its cytocompatibility.

• Klíčová slova
• Biocompatible magnesium alloy, Cytocompatibility, Severe shot peening, Surface grain refinement,
• MeSH
• elektrochemie MeSH
• koroze MeSH
• kultivované buňky MeSH
• lidé MeSH
• nanostruktury chemie   ultrastruktura   MeSH
• osteoblasty cytologie   účinky léků   MeSH
• povrchové vlastnosti MeSH
• slitiny farmakologie   MeSH
• testování materiálů metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• Mg-Al-Zn-Mn-Si-Cu alloy MeSH Prohlížeč
• slitiny MeSH

Deformation behaviour of rolled AZ31 sheets that were subjected to the accumulative roll bonding was investigated. Substantially refined microstructure of samples was achieved after the first and second pass through the rolling mill. Sheets texture was investigated using an X-ray diffractometer. Samples for tensile tests were cut either parallel or perpendicular to the rolling direction. Tensile tests were performed at temperatures ranging from room temperature up to 300 °C. Tensile plastic anisotropy, different from the anisotropy observed in AZ31 sheets by other authors, was observed. This anisotropy decreases with an increasing number of rolling passes and increasing deformation temperature. Grain refinement and texture are the crucial factors influencing the deformation behaviour.

• Klíčová slova
• accumulative roll bonding, dynamic recrystallization, magnesium alloy, tensile anisotropy, texture, twinning,
• Publikační typ
• časopisecké články MeSH

The primary objective of this study is to investigate the microstructural, mechanical, and wear behaviour of AZ31/TiC surface composites fabricated through friction stir processing (FSP). TiC particles are reinforced onto the surface of AZ31 magnesium alloy to enhance its mechanical properties for demanding industrial applications. The FSP technique is employed to achieve a uniform dispersion of TiC particles and grain refinement in the surface composite. Microstructural characterization, mechanical testing (hardness and tensile strength), and wear behaviour evaluation under different operating conditions are performed. Response surface methodology (RSM) is utilized to optimize the wear rate by considering the effects of process parameters. The results reveal a significant improvement in hardness (41.3%) and tensile strength (39.1%) of the FSP-TiC composite compared to the base alloy, attributed to the refined grain structure (6-10 μm) and uniform distribution of TiC particles. The proposed regression model accurately predicts the wear rate, with a confirmation test validating an error percentage within ± 4%. Worn surface analysis elucidates the wear mechanisms, such as shallow grooves, delamination, and oxide layer formation, influenced by the applied load, sliding distance, and sliding velocity. The enhanced mechanical properties and wear resistance are attributed to the synergistic effects of grain refinement, particle-accelerated nucleation, the barrier effect of TiC particles, and improved interfacial bonding achieved through FSP. The optimized FSP-TiC composites exhibit potential for applications in industries demanding high strength, hardness, and wear resistance.

• Klíčová slova
• AZ31 alloy, Friction stir processing, Hardness, Microstructure, Tensile properties, TiC particles, Wear optimization,
• Publikační typ
• časopisecké články MeSH

In this study, the effect of ultrasonic vibration during Friction Stir Vibration Processing (FSVP) on the microstructure and mechanical behaviour of AZ31/TiC surface composites was investigated. Specifically, Titanium Carbide (TiC) particles were introduced as a reinforcement (15 vol%) into the magnesium alloy AZ31 using both Friction Stir Processing (FSP) and FSVP. Comprehensive examinations were carried out to analyse the microstructure, hardness, and tensile behaviour of the resulting composites. The study revealed significant improvements in mechanical properties due to the application of ultrasonic vibration during FSP. Firstly, the stir zone region was found to be free from voids, enhancing material flow and promoting even dispersion of TiC powders within the matrix. Secondly, refinement of grains was observed due to dynamic recrystallization and the pinning effect imposed by TiC particles, leading to the formation of more dislocations in the composite and indicating a considerable alteration in the material's structure. Importantly, the vibration during FSP introduced an auxiliary energy source, resulting in a remarkable enhancement in both hardness and tensile strength. Compared to the AZ31/15 vol% TiC FSP composite, the composites produced via FSVP exhibited a grain size reduction of about 64% and improvements in hardness and ultimate tensile strength (UTS) of about 55% and 21%, respectively. Notably, these improvements were achieved without compromising the ductility of the composite, which remained at appreciable levels.

• Klíčová slova
• AZ31, FSP, FSVP, Mechanical properties, magnesium, ultrasonic vibration,
• Publikační typ
• časopisecké články MeSH

Commercially available AZ31 magnesium alloy was four times extruded in an equal rectangular channel using three different routes (A, B, and C). Micro tensile deformation tests were performed at room temperature with the aim to reveal any plastic anisotropy developed during the extrusion. Samples for micro tensile experiments were cut from extruded billets in different orientations with respect to the pressing direction. Information about the microstructure of samples was obtained using the electron back-scatter diffraction (EBSD) technique. Deformation characteristics (yield stress, ultimate tensile stress and uniform elongation) exhibited significant anisotropy as a consequence of different orientations between the stress direction and texture and thus different deformation mechanisms.

• Klíčová slova
• equal channel angular pressing, magnesium alloy, miniaturized tensile tests, processing route, slip systems, twinning,
• Publikační typ
• časopisecké články MeSH

Dry sliding wear behaviour of friction stir processed (FSP) AZ31 and AZ31/ZrC particles (5, 10, and 15 vol%) reinforced surface composite was investigated at different sliding speeds and loads. The samples were tested using a pin-on-disc apparatus with EN31 steel as the counter body to determine the role of FSP and ZrC reinforcement on the microstructure, hardness, and wear behaviour of AZ31. Base metal AZ31 alloy exhibits a hardness of 60 HV, whereas the 15 vol% ZrC-reinforced composites had the highest hardness of 108 HV. It was also identified that 15 vol% ZrC-reinforced composites exhibited lowest wear rate and friction coefficient under all testing conditions. Abrasion, delamination, oxidation, material softening, and plastic deformation are the primary wear mechanisms viewed from the wear tracks of the samples. Higher volume fraction of ZrC particles exhibited better wear resistance at all speeds and loads than AZ31 alloy. A wear map has been generated for different material compositions and wear conditions to identify the main wear mechanisms easily.

• Publikační typ
• časopisecké články MeSH

Two novel ignition-resistant magnesium alloys, Mg-2Gd-2Y-1Ca and Mg-2Nd-1Y-1Ca, were prepared in the ultrafine-grain condition by equal channel angular pressing (ECAP). In addition, four commercial alloys-AZ31, AX41, AE42 and WE43-were prepared similarly as a reference. The microstructure, mechanical properties and ignition temperature were thoroughly investigated. Both novel alloys exhibited a mean grain size of ~1 µm and dense distribution of small secondary phase particles. The mechanical strength measured by the tensile deformation test showed that the novel alloys are much stronger (~290 MPa) than all commercial alloys except WE43. However, Ca segregation into the grain boundaries caused a significant decrease in ductility (<6%). The ignition temperature of the novel alloys (~950 °C) was considerably improved by the presence of Gd/Nd, Y and Ca. This study showed that both novel alloys exhibit high strength and high ignition temperature in the ultrafine-grain condition.

• Klíčová slova
• flammability resistance, magnesium, mechanical properties, microstructure, ultrafine-grain,
• Publikační typ
• časopisecké články MeSH