关键词： corrosion behavior   EIS   magnesium alloy   orientation   simulated body fluid  

摘要： Two orientation samples were prepared along the normal (ND) and transverse (TD) directions of the rolled AZ80 magnesium alloy. The samples (ND and TD) were immersed in simulated body fluid (SBF) for long-term (25 days) immersion test. Electrochemical measurements such as electrochemical impedance spectroscopy and potentiodynamic polarization test were conducted to study the electrochemical behavior. Scanning electron microscopy and energy-dispersive x-ray spectrometer were used to investigate the corrosion morphology and chemical composition of samples during various immersion processes. X-ray diffraction was employed to identify the texture composition. The results indicated that severe localized corrosion occurred in the ND sample. Uniform corrosion was the dominant corrosion in the TD sample. The TD sample exhibited better corrosion performance (higher corrosion resistance and lower corrosion rate) than the ND sample. The corrosion behavior of magnesium alloy was closely related to texture, microstructure, and corrosion product film. The influence mechanism of texture and microstructure on corrosion behavior of magnesium alloy was discussed.

关键词： Magnesium alloys  

摘要： The in vivo fast degradation and poor biocompatibility are two major challenges of the magnesium alloys in the field of artificial bone materials. In this study, graphene oxide (GO) was first functionalized by chitosan (GOCS) and then immobilized on the magnesium alloy surface, finally the complex of heparin and bone morphogenetic protein 2 was incorporated on the modified surface to synergistically improve the corrosion resistance, anticoagulation, and osteogenesis. Apart from an excellent hydrophilicity after the surface modification, a sustained heparin and BMP2 release over 14 days was achieved. The corrosion resistance of the modified magnesium alloy was significantly better than that of the control according to the results of electrochemical tests. Moreover, the corrosion rate was also significantly reduced in contrast to the control. The modified magnesium alloy not only had excellent anticoagulation, but also can significantly promote osteoblast adhesion and proliferation, upregulate the expression of alkaline phosphatase and osteocalcin, and enhance mineralization. Therefore, the method of the present study can be used to simultaneously improve the corrosion resistance and biocompatibility of the magnesium alloys targeted for the orthopedic applications. [GRAPHICS] . Highlights The GOCS@Hep/BMP2 bioactive coating was created on the magnesium surface. The coated magnesium alloy had good wettability and corrosion resistance. The coating can improve anticoagulation and osteogenesis of magnesium

关键词： Composite coatings  

摘要： The bacterial infection of bone implants is a vital factor leading to implant failure. Superhydrophobic surface with low adhesion can effectively enhance corrosion resistance and antibacterial adhesion properties of magnesium alloy. Herein, the superhydrophobic composite coating of hydroxyapatite (HA)/stearic acid was successfully prepared on magnesium alloy (AZ31B) using hydrothermal method and followed modification of stearic acid. The wettability, corrosion resistance and antibacterial adhesion capacity of the composite coating were studied. The composite coatings confer excellent superhydrophobicity with a contact angle about 152.52 degrees and a sliding angle about 2 degrees, and showed good long-term superhydrophobic stability in air. Meanwhile, during immersion in simulated body fluid (SBF), the superhydrophobic composite coating was converted to hydrophilicity in a short time and exposed the micro-/nano-scale structure surface of HA, which could induce the fast deposition of the mineralized apatite layer. The characteristics endowed the composite coating with the short-term antibacterial adhesion property and long-term corrosion resistance in SBF, which will afford a surface modification strategy for the application of magnesium alloy implants in orthopedics and dentistry.

关键词： magnesium alloys   rare earth metals   reversion after aging   solid solution decomposition  

摘要： The parameters of reversion after hardening aging of magnesium alloys containing two rare earth metals gadolinium (yttrium group) and samarium (cerium group) were determined at various ratios of their contents. The reversion was observed at short annealing at 250 and 300 degrees C beginning with 5 min after preliminary aging at 200 degrees C up to maximum hardening and consisted of significant softening of the alloys then. Measurements of the electrical resistance indicated that during softening the reverse dissolution of the rare earth metals in magnesium-based solid solution takes place with diminution of the quantity of hardening particles precipitated during aging beforehand. The reverse dissolution of the rare earth metals in solid magnesium increases with increase in the annealing temperature after aging from 250 to 300 degrees C and with increase in the gadolinium to samarium ratio in the alloys.

关键词： Temperature field   Numerical study   DC casting   Pulsed magnetic field   Velocity fluctuation  

摘要： Purpose The purpose of this paper is to investigate the effect of pulsed magnetic field (PMF) with different duty cycles on the melt flow and heat transfer behaviors during direct-chill (DC) casting of large-size magnesium alloy billet and find the appropriate range of duty cycle. Design/methodology/approach A transient two-dimensional mathematical model coupled electromagnetic field, flow field and thermal field, is conducted to study the melt flow and temperature field under PMF and compared with that under the harmonic magnetic field. Findings The results reveal that melt vibration and fluctuation are generated due to the instantaneous impact of repeated thrust and pull effects of Lorentz force under PMF. The peak of Lorentz force decreases greatly with the increasing duty cycle, but the melt fluctuation region is expanded with higher duty cycle, which accelerates the interior melt velocity and reduces the temperature gradient at the liquid-solid interface. However, PMF with overly high duty cycle has adverse effect on the melt convection and limited influence on the interior melt. A duty cycle of 20% to 50% is a reasonable range. Practical implications This paper can provide guiding significance for the setting of duty cycle parameters on DC casting under PMF. Originality/value There are few reports on the effect of PMF parameters during DC casting with applying PMF, especially for duty cycle, a parameter unique to PMF. The findings will be helpful for applying the external field of PMF on DC casting.

关键词： Refill friction stir spot welding   magnesium alloy   temperature field   material flow   microstructure  

摘要： Temperature distribution and material flow behaviours during refill friction stir spot welding (RFSSW) of AZ91D magnesium alloy were studied by a combination of numerical modelling and experimentation. The coupled Eulerian-Lagrangian (CEL) formulation was adopted to analyse processing thermal history and plastic deformation mechanisms of the RFSSW joint more accurately. Welding thermal cycles of varying positions in joint were measured by thermocouples so as to validate accuracy of this simulation process. The FEA (Finite Element Analysis) simulation to cover mechanical results was found to be consistent with the experimental values. Moreover, simulation analysis presented that material flow caused the clear hook defects and bonding ligament, and such material flow behaviours were experimentally verified via the macrostructure and microstructure of the RFSSW joint.

关键词： Friction stir welding   ME20M magnesium alloy   preheating   thermal history   microstructure   mechanical properties   fracture  

摘要： Friction stir welding (FSW) of ME20M magnesium alloy without and with preheating in different temperatures is carried out. The thermal histories of different preheating temperatures are investigated;the microstructure and mechanical properties of the weld joints are studied. The results show that by increasing the preheating temperature, the peak temperature, the grain size as well as the precipitate size are increased, and the precipitation is reduced. After FSW, the preferred orientation of the (0001) crystal direction changes not to parallel but to normal direction, and the texture intensity improves. The microhardness and the tensile strength of the joints first increase and then decrease with the increase of the preheating temperature.

关键词： Severe plastic deformation   Strain path   Constrained groove pressing   Microstructure   Mechanical properties   AZ31 magnesium alloy sheets  

摘要： Constrained groove pressing (CGP) is a novel severe plastic deformation (SPD) method suitable for fabricating ultra-fine grained (UFG) sheet metals. In this work, two passes of CGP were conducted to AZ31 magnesium alloy sheets at 523 K, and three routes including traditional CGP, 180 degrees cross-CGP and 90 degrees cross-CGP were employed to investigate the effects of pressing number and strain path on microstructure, texture and mechanical properties of the alloy sheets. The results show that, irrespective of CGP routes, a bimodal microstructure is developed in the deformed materials and the capability of CGP in fabricating UFG magnesium alloy sheets is confirmed by TEM observation. The superior grain refinement and microstructure homogenization is achieved in traditional CGP route from the as-annealed 9.85 mu m-5.04 mu m after one pass while no further improvement is observed after two passes. The average grain sizes are 5.69 mu m and 5.18 mu m after two passes of 180 degrees cross-CGP and 90 degrees crossCGP, respectively. The average misorientation angle is mainly determined by the fraction of very high angle grain boundaries and texture and microstructure mechanisms dominate the generation of high angle grain boundaries in traditional and cross-CGP routes, respectively. The coexistence of strain free recrystallized grains and substructured/deformed grains is observed after one pass of traditional CGP due to incomplete dynamic recovery and dynamic recrystallization and promotes the subsequent activation of strain induced grain boundary migration, which may be postponed by employing cross-CGP routes. A double-peak basal texture with the basal poles inclined from ND to RD is developed in traditional CGP route while an inclination of the basal poles from ND to TD accompanied by a redistribution of the prismatic intensity toward RD is observed in cross-CGP routes due to the change of shear deformation direction. The texture softening plays a more important role in

关键词： Corrosion inhibitor   AZ91D magnesium alloy   asym-pyrazolium ionic liquid   Inhibition mechanism   Density functional theory  

摘要： Three pyrazolium ionic liquids 1-n-butyl-2-hexylpyrazole bis(trifluoromethylsulfonyl)amide ([BHPz]NTf2]), 1-n-butyl-2-octylpyrazole bis(trifluoromethylsulfonyl)amide ([BOPz][Nrf(2)]), and 1-n-butyl-2-dccylpyrazole bis(trifluoromethylsulfonyl)amide ([BDePz][NTf2]) are firstly synthesized and their corrosion inhibition for AZ91D magnesium alloys in 0.05 wt% NaCl solution is investigated. The highest inhibition efficiency is 90.0% under optimal test conditions. The inhibition performance is measured by electrochemical tests, and follows the Langmuir adsorption model. The surface morphology is determined by scanning electron microscopy (SEM) and atomic force microscopy (AFM), which testifies the formation of protective films on Mg alloy surface. The possible inhibited mechanism is proposed according to X-ray photoelectron spectroscopy (XPS) analysis and the density functional theory (DFT) calculation. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Magnesium alloy   Aging   Damping capacity   beta(1)' phase  

摘要： A Z new approach to improve the damping capacity and mechanical properties of ZK60 magnesium alloy at the same time is discovered by introducing the beta(1)' (MgZn2) precipitates. The beta(1)' precipitates are formed in the alloy experienced solution treatment and subsequent aging at 140 degrees C for 18 h in this study. The synchronous improvement in mechanical and damping properties of the alloy is mainly due to the coherent orientation relationships between the beta(1)' phase and the a-Mg matrix, and the shearing or bypassing of dislocations on the beta(1)' precipitates depending on their sizes and spacing. The modified Granato-Lucke (G-L) model is presented in this work to analyze the favorable damping capacity of the as-aged ZK60 alloy and the interaction between the beta(1)' precipitates and the mobile dislocations is a new source of energy-dissipation.