Corrosion Fatigue of Fine Grain Mg-Zn-Zr and Mg-Y-Zn Alloys

Corrosion fatigue data for magnesium alloys are still scarce. The present communication reports the results of microstructural investigations and fatigue testing of the fine grain Mg-Zn-Zr (ZK60) alloy after multiaxial isothermal forging and of the hot extruded Mg-Y-Zn (WZ21) alloy in air and in the 0.9% NaCl water solution. Both of the alloys demonstrate a very good high-cycle fatigue performance in air. However, the significant drop of fatigue resistance is observed in the corrosive environment. Results are discussed from perspectives of potential applications and future studies

Evolution of Mechanical Twinning during Cyclic deformation of Mg-Zn-Ca Alloys

The present study clarifies the complex interplay between mechanical twinning and dislocation slip during low-cycle fatigue testing of Mg-Zn-Ca alloys. Temporal details of these mechanisms are studied non-destructively by in situ monitoring of the acoustic emission (AE) response powered by a robust signal categorization. Through the analysis of AE time series, the kinetics of deformation twinning per cycle and the overall accumulation of twinning during cyclic loading is described and its effect on fatigue life is highlighted

Corrosion Fatigue of Fine Grain Mg-Zn-Zr and Mg-Y-Zn Alloys

Corrosion fatigue data for magnesium alloys are still scarce. The present communication reports the results of microstructural investigations and fatigue testing of the fine grain Mg-Zn-Zr (ZK60) alloy after multiaxial isothermal forging and of the hot extruded Mg-Y-Zn (WZ21) alloy in air and in the 0.9% NaCl water solution. Both of the alloys demonstrate a very good high-cycle fatigue performance in air. However, the significant drop of fatigue resistance is observed in the corrosive environment. Results are discussed from perspectives of potential applications and future studies

Evolution of Mechanical Twinning during Cyclic Deformation of Mg-Zn-Ca Alloys

The present study clarifies the complex interplay between mechanical twinning and dislocation slip during low-cycle fatigue testing of Mg-Zn-Ca alloys. Temporal details of these mechanisms are studied non-destructively by in situ monitoring of the acoustic emission (AE) response powered by a robust signal categorization. Through the analysis of AE time series, the kinetics of deformation twinning per cycle and the overall accumulation of twinning during cyclic loading is described and its effect on fatigue life is highlighted

Fatigue Performance of Mg-Zn-Zr Alloy Processed by Hot Severe Plastic Deformation

Fatigue properties under axisymmetric push-pull loading of a magnesium alloy Mg-6Zn-0.5Zr (ZK60) after processing by multiaxial isothermal forging (MIF) to a total strain of 4.2 at 400 °C were investigated. The strong influence of the microstructure on the mechanical behavior is demonstrated. Hot severe plastic deformation was shown effective in improving the fatigue life in both the high- and low-cyclic regimes

The processing route towards outstanding performance of the severely deformed Al–Mg–Mn-Sc-Zr alloy

Aiming at obtaining the enhanced mechanical properties profile for lightweight applications, bulk billets of the commercial 1570C aluminium alloy (Al–5Mg-0.18Mn-0.20Sc-0.08Zr, wt. %) with nanosized aluminides of transition metals (TM) were subjected to various thermomechanical treatments comprising severe plastic deformation for grain refinement and favourable distribution of disperse phases. The potential of multiaxial isothermal forging (MIF) for the fabrication of ultrafine-grain advanced aluminium alloys is unveiled via a multistep pathway involving two primary routes – the one under constant processing temperature and the other with the inter-step temperature reduction from 325 to 175 °C - combined with conventional cold rolling or high-pressure torsion. Processing-dependent microstructural factors controlling the alloy's behaviour under monotonic and cyclic loading at ambient temperature are discussed with the account of the role of the grain size, grain boundary distribution, precipitates of Mg-rich β-phase and TM-aluminides. In particular, it is shown that after MIF followed by cold rolling, the outstanding combination of the tensile strength and ductility was observed concomitantly with the fatigue resistance superior to that in the contemporary alloys of the same class and/or of many currently available commercial high-strength alloys

On the Corrosion Fatigue of Magnesium Alloys Aimed at Biomedical Applications: New Insights from the Influence of Testing Frequency and Surface Modification of the Alloy ZK60

Magnesium alloys are contemporary candidates for many structural applications of which medical applications, such as bioresorbable implants, are of significant interest to the community and a challenge to materials scientists. The generally poor resistance of magnesium alloys to environmentally assisted fracture, resulting, in particular, in faster-than-desired bio-corrosion degradation in body fluids, strongly impedes their broad uptake in clinical practice. Since temporary structures implanted to support osteosynthesis or healing tissues may experience variable loading, the resistance to bio-corrosion fatigue is a critical issue that has yet to be understood in order to maintain the structural integrity and to prevent the premature failure of implants. In the present communication, we address several aspects of the corrosion fatigue behaviour of magnesium alloys, using the popular commercial ZK60 Mg-Zn-Zr alloy as a representative example. Specifically, the effects of the testing frequency, surface roughness and metallic coatings are discussed in conjunction with the fatigue fractography after the testing of miniature specimens in air and simulated body fluid. It is demonstrated that accelerated environmentally assisted degradation under cyclic loading occurs due to a complicated interplay between corrosion damage, stress corrosion cracking and cyclic loads. The occurrence of corrosion fatigue in Mg alloys is exaggerated by the significant sensitivity to the testing frequency. The fatigue life or strength reduced remarkably with a decrease in the test frequency

Monitoring Dynamic Recrystallisation in Bioresorbable Alloy Mg-1Zn-0.2Ca by Means of an In Situ Acoustic Emission Technique

The tensile behaviour of the biocompatible alloy Mg-1Zn-0.2Ca (in wt.%) in the fine-grained state, obtained by severe plastic deformation via multiaxial isothermal forging, has been investigated in a wide range of temperatures (20 ÷ 300) °C and strain rates (5 × 10−4 ÷ 2 × 10−2) s−1 with the measurements of acoustic emission (AE). The dependences of mechanical properties, including the yield stress, ultimate strength, ductility, and the strain-hardening rate, on the test temperature and strain rate, were obtained and discussed. It is shown for the first time that an acoustic emission method is an effective tool for in situ monitoring of the dynamic recrystallisation (DRX) process. The specific behaviour of the acoustic emission spectral density reflected by its median frequency as a function of strain at various temperatures can serve as an indicator of the DRX process’s completeness

Attaining High Functional Performance in Biodegradable Mg-Alloys: An Overview of Challenges and Prospects for the Mg-Zn-Ca System

This article presents a concise overview of modern achievements and existing knowledge gaps in the area of biodegradable magnesium alloys. Hundreds of Mg-based alloys have been proposed as candidates for temporary implants, and this number tends to increase day by day. Therefore, while reviewing common aspects of research in this field, we confine ourselves primarily to the popular Mg-Zn-Ca system, taken as a representative example. Over the last decades, research activities in this area have grown enormously and have produced many exciting results. Aiming at highlighting the areas where research efforts are still scarce, we review the state-of-the-art processing techniques and summarize the functional properties attained via a wide variety of processing routes devised towards achieving a desired properties profile, including the mechanical response in terms of strength, ductility, and fatigue resistance paired with biocompatibility and bio-corrosion resistance or controlled degradability. We pay keen attention to a summary of corrosion properties and mechano-chemical interactions between an aggressive environment and loaded Mg-based structures, resulting in stress corrosion cracking and premature corrosion fatigue failures. The polemic issues and challenges practitioners face in their laboratory research are identified and discussed

Attaining High Functional Performance in Biodegradable Mg-Alloys: An Overview of Challenges and Prospects for the Mg-Zn-Ca System

This article presents a concise overview of modern achievements and existing knowledge gaps in the area of biodegradable magnesium alloys. Hundreds of Mg-based alloys have been proposed as candidates for temporary implants, and this number tends to increase day by day. Therefore, while reviewing common aspects of research in this field, we confine ourselves primarily to the popular Mg-Zn-Ca system, taken as a representative example. Over the last decades, research activities in this area have grown enormously and have produced many exciting results. Aiming at highlighting the areas where research efforts are still scarce, we review the state-of-the-art processing techniques and summarize the functional properties attained via a wide variety of processing routes devised towards achieving a desired properties profile, including the mechanical response in terms of strength, ductility, and fatigue resistance paired with biocompatibility and bio-corrosion resistance or controlled degradability. We pay keen attention to a summary of corrosion properties and mechano-chemical interactions between an aggressive environment and loaded Mg-based structures, resulting in stress corrosion cracking and premature corrosion fatigue failures. The polemic issues and challenges practitioners face in their laboratory research are identified and discussed