关键词： Magnesium alloys   fine grains   hardness   tensile strength   wear  

摘要： ZE41 magnesium alloy was successfully produced by friction stir processing and grain refinement was achieved from a starting size of 107 mu m +/- 6.7 mu m to 3.5 mu m +/- 1.5 mu m. MgZn intermetallic which was appeared as network like structure at the grain boundaries before friction stir processing was greatly affected due to the severe plastic deformation and broken as small particles as observed from the microstructural studies. Higher hardness (approximate to 30 %) was measured for the fine grained ZE41 magnesium alloy compared with the base alloy due to the grain refinement. From the tensile tests, yield strength and ultimate tensile strength was significantly increased at the cost of decreased ductility reflected in lower strain for the fine grained ZE41 compared with the base alloy. Wear studies showed higher coefficient of friction and lower mass loss for the grain refined ZE41 magnesium alloy. From the results, it can be understood that the grain refinement achieved by friction stir processing has a profound influence on enhancing the mechanical and tribological properties of ZE41 magnesium alloy.

关键词： AZ31B Mg alloy   Hybrid inhibitor   Synergistic effect   Inhibitory mechanism   Density functional theory  

摘要： L-Phenylalanine (L-Phe) is a promising eco-friendly alternative to replace the conventional toxic inhibitors for magnesium alloys in NaCl solution. However, its inhibitory performance is not satisfied. The addition of slight amount Zn(NO3)2 would greatly refine the inhibitory efficiency. The inhibitory performance of hybrid inhibitor is explored by scanning electron microscopy (SEM) along with energy dispersive X-ray spectroscopy (EDS), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and various electrochemical measurements. The highest inhibitory efficiency of 93.2% is achieved for 0.30 mM L-Phe + 0.07 mM Zn(NO3)2. The amount of each inhibitor and the suitable match of two inhibitors are carefully determined, which are both critical items for the final performance. The possible inhibitory mechanism is conjectured by the XRD and XPS measurements along with the quantum chemical calculations. (c) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

关键词： Zerilli-Armstrong   Orthogonal cutting   Flow stress   Magnesium   HCP   AZ31B  

摘要： This work reports on a methodology to extend Oxley's analysis of the thick shear zone to account for HCP materials. Ultimately, the work extracts Zerilli-Armstrong (ZA) constitutive equation' material parameters for AZ31B, an HCP crystal structure magnesium-based alloy. The methodology for accomplishing this utilizes three tasks namely: 1) Extension of thick shear zone approach for machining force simulation to account for Zerilli-Armstrong HCP material model, 2) measure cutting and thrust edge forces from orthogonal cutting tests (uncut chip thickness and cutting speed values varying between 0.05 and 0.4 mm/rev and 50-400 m/min, respectively), and 3) numerically determine updated material model parameters for AZ31B by minimizing the difference between the methodology-predicted forces and those experimentally measured. Comparing numerical data with the experiments, the determined AZ31B material model with updated parameters yielded predictability of R-2 of 0.94 and 0.91 for cutting and thrust forces, respectively. Additional validations were conducted by favorably comparing flow stress numerical predictions for AZ31B with literature-published histories at wide operating ranges of temperature, strain, and strain rate values. The presented methodology for finding HCP Zerilli-Armstrong material model parameters based on orthogonal cutting tests may serve as complementary alternative to time-consuming tension-compression flow stress experiments.

关键词： dislocations   DSA effect   Mg alloys   strain hardening   temperature effect  

摘要： Herein, the effect of temperature on strain-hardening behaviors of binary Mg-3X (X = Al, Zn, Sn, Y, and Gd) alloys were investigated. Uniaxial tensile tests are carried out at room temperature (RT), 150 and 250 degrees C. These samples are composed of a-Mg phase and second-phase precipitates which exist only in Mg3Sn and Mg-3Gd. In the temperature range of this work, dislocation movement dominates the plastic deformation process and strain-hardening ability decreases with rising temperature due to stronger dynamic recovery. The amount of forest dislocations decreases at elevated temperature under the influence of dynamic recovery and grain boundary sliding (GBS), thus strain-hardening ability is seriously weakened. However, a periodic serrated hardening curve appears in Mg-3Y and Mg-3Gd alloys at elevated temperature, which results from dynamic strain aging (DSA) effect. Moreover, with increasing deformation temperature, the decline scope of strain-hardening ability of Mg-3Y and Mg-3Gd is significantly lesser than non-RE binary alloys. The differences in strain-hardening behavior of these alloys at various temperatures are mainly related to diffusion coefficients of alloying elements in alpha-Mg matrix.

关键词： Magnesium alloy   Reactive friction stir processing   In situ reaction   Aging treatment  

摘要： In this study, reactive friction stir processing (RFSP) was applied for AZ31B Mg alloy to improve their inferior strength and corrosion resistance. A high-Al alloying layer was successfully fabricated on rolled AZ31B plate surface through multipass RFSP reacting the additive pure Al powder (3 ?m diameter) along its groove line. During RFSP, the Al powder was completely dissolved into the ?-Mg matrix and reacted in situ with the ?-Mg matrix to produce Mg17Al12 precipitates. With the strengthening effects by the solid solution of supersaturated Al and in situ Mg17Al12 precipitates, RFSP improved the hardness, yield strength, and ultimate tensile strength of the as-received AZ31B by 58%, 34%, and 15%, respectively. Furthermore, aging treatment was conducted after RFSP, inducing a lamellar-shaped Mg17Al12 in the RFSPed layer. The additional strengthening effect by the aging-induced Mg17Al12 resulted in further improvement in the hardness (15%, 97 Hv) and yield strength (13%, 102 MPa) compared to the RFSPed layer. However, the ultimate tensile strength deteriorated due to the too high fraction of aging-induced Mg17Al12 precipitates that caused a premature fracture. The results of the hydrogen evolution measurements and electrochemical impedance spectroscopy showed that RFSP and subsequent aging treatment enhanced the corrosion resistance due to the corrosion barrier effect of the in situ and aging-induced Mg17Al12.

关键词： Magnesium alloys   Age hardening   Precipitation   Deformation  

摘要： Certain magnesium alloy systems can obtain superior mechanical strength through age hardening. However, conventional ageing heat treatments for these alloys are rarely more complex than a single isothermal hold - especially when compared to those of aluminium alloys - so age hardenable magnesium alloys may not be achieving their full strengthening potential. The use of preageing, where a lower temperature heat treatment is utilised before a hotter secondary ageing step, has proven successful in boosting the strength of magnesium alloys previously, but these trials are few in number, and the testing conditions are limited. In this work, a wide range of preageing temperatures and times were trialled on commercial and experimental magnesium alloys to determine the effectiveness of the strengthening technique. The results showed that preageing can produce a significant boost in hardness, can reduce total ageing times, and can provide a degree of mechanical property customisation through control of precipitate habit plane and morphology. However, the effectiveness of the technique is alloy-system dependent, where the fundamental precipitate nucleation and phase evolution is a key contributor to the success of preageing;as is the energy barrier to nucleation in an alloy system, whether that be controlled by alloy chemistry or thermomechanical processing. The results are discussed in the context of alloy design and industrial processing.

关键词： Biodegradable magnesium alloys   Coatings   Corrosion   Chemical conversion   Nanocrystalline zinc  

摘要： Biodegradable medical implants made of magnesium (Mg) alloys must have sufficient corrosion resistance in clinical applications. Herein, a nanocrystalline zinc (Zn) coating is electrodeposited on the WE43 Mg alloy followed by a chemical conversion treatment to produce a titania-Zn phosphate layer. The Zn coating has a rice-like nanostructure and the conversion layer is composed of ZnO, Zn-3(PO4)(2), and TiO2. The Zn coating reduces the corrosion current density of the WE43 Mg alloy from 151.1 +/- 13.8 mu A cm(-2) to 29.4 +/- 7.4 mu A cm(-2) in the simulated body fluid (SBF), while the composite coating decreases it to 4.1 +/- 0.8 mu A cm(-2). The surface morphology, pH variation, and average corrosion rates after immersion for 7 days in SBF reveal that the Zn coating in fact accelerates dissolution of the Mg substrate due to the formation of galvanic couples between the Zn coating and Mg alloy substrate. In comparison, only slight corrosion is observed from limited areas on the sample with the composite coating. The titania-Zn phosphate/nanocrystalline Zn composite coating provides long-term protection in the physiological environment and the protection mechanism is discussed.

关键词： Fine-grained   Extrusion   Tension   Compression   Texture  

摘要： The deformation behavior of an extruded Mg-Zn-Zr alloy in the form of plate/sheet was investigated on the basis of fine-grained and initial macro-texture along various directions under uniaxial compression and tension test. The initial macro-texture revealed that 60.4% of grains have c-axes of hexagonal closed packed crystal structure along the normal direction and 17.4% grains have c-axes parallel to the transverse direction. The results showed that the flow stress and strain hardening rate under compression and tension were significantly affected by the loading directions and the initial texture. The ratio of tensile yield strength to the compressive yield strength along normal direction extruded direction, and transverse direction was found 0.85, 1.5, and 0.93, respectively. The practically symmetric yielding behavior along normal and transverse direction was caused by the fine-grained size, twinning dependencies on strain path loading, and texture. The anisotropy similar to 1.5 along extrusion direction is the cause of the large fraction of {10 (1) over bar2} <10<(1)over bar>1 > extension twinning under compression and no twinning activity in tension along ED in the early stages of deformation in large grains. The strain hardening curves under tension and compression shows almost similar behavior in the normal direction. For extrusion direction and transverse direction, strain hardening curves exhibited three and two regimes under compressive loading which leads to a large difference in ultimate compressive and tensile strength. It is also revealed that {10 (1) over bar2} < 10<(1)over bar>1> extension twinning was favorable, while {10 (1) over bar1} <10<(1)over bar>2 > contraction twinning and {10 (1) over bar1} - {10 (1) over bar2} double twinning were unfavorable for strain hardening. The underlying deformation mechanisms under different loading paths were discussed on the basis of X-ray diffraction and optical microscopic analysis. (C) 2020 Elsevier B.V. All

关键词： Magnesium   Biodegradation   PEO   Corrosion   Wear  

摘要： The rapid bio-corrosion of magnesium-based alloys, the formation of hydrogen gas and, consequently, the premature loss of biomechanical functions hinder their applications as biodegradable implant materials. The corrosion becomes even accelerated, when fretting wear occurs at implant junctions, as a result of repeated disruptions of the magnesium (hydr)oxide layer formed on implant surfaces. To improve the overall performance of these materials in a bio-relevant environment, especially corrosion resistance and wear resistance, in this research, plasma electrolytic oxidation (PEO) was applied to create a coating on a magnesium alloy, ZK30. The resulting gains in corrosion resistance and wear resistance were evaluated. In vitro immersion tests in Hank's solution at 37 degrees C showed a reduction in hydrogen release from the PEO-treated alloy. The results obtained from applying the scanning vibrating electrode technique (SVET) indicated a decreased susceptibility of the PEO-treated alloy to localized corrosion, accounting for the improved corrosion resistance. In addition, PEO was found to change the surface topography and roughness, in addition to surface chemistry, which contributed to an increased but stable coefficient of friction and a decreased material removal rate, as revealed by the tribological tests with a ball-on-plate configuration. The results indicate an enlarged opportunity of magnesium-based materials for orthopedic applications, where friction and wear are involved, by applying PEO.

关键词： Mg alloy   Strength   Ductility   Corrosion   Precipitate  

摘要： It is always challenging to synchronously improve the strength, ductility and corrosion resistances, in the development of magnesium alloys. Herein, a concept called hierarchical precipitate embedded fine grain microstructure is proposed and implemented in an Mg-13Al (wt%) alloy by equal channel angular pressing and aging. Compared to the as-cast alloy, the modified alloy with the designed microstructure has high strength, good ductility, and improved corrosion resistance. The enhancement of mechanical properties is mainly attributed to the synergistic effect of fully recrystallized fine grains (similar to 3.7 mu m) and hierarchical beta phase (Mg17Al12) precipitates. Although the formation of the hierarchical beta phase precipitates in fine-grain Mg matrix can accelerate the initial corrosion in 3.5 wt% NaCl solution due to the galvanic corrosion, the ultimate corrosion resistance is successfully improved by the consumption of exposed Mg anodes and the synergistic barrier effect from the newly-formed corrosion products and corrosion-resistant beta phases. (C) 2020 Elsevier B.V. All rights reserved.