关键词： Corrosion resistance   Electroless nickel   Magnesium alloy   Microarc oxidation   Molecular dynamics simulation   Self-assembly  

摘要： A microarc oxidation (MAO) film was prepared on the surface of magnesium alloy by using microarc oxidation technology. Three kinds of self-assembled films with different hydrophobicities were prepared on the surface of the MAO film by self-assembly (SAM) technology using different self-assembled molecules. The static contact angle tests determined that the contact angles of the self-assembled films were 33.71 degrees, 93.99 degrees, and 140.46 degrees. After that, three layer composite coatings were successfully prepared by electroless nickel (EN) technology. SEM, EDS, XRD and XPS were used to characterize the surface morphology and composition of the samples. The Mott Schottky (M-S) curves characterize the semiconductor properties of the samples. The electrochemical test evaluates the corrosion resistance of the samples. The results show that the characteristic peaks of Ni were detected on the surfaces of the three three-layer composite coatings, and the electroless nickel plating layer was successfully prepared on the surface of MAO/SAM layers with different hydrophobicity. The better the hydrophilicity of the self-assembled layer is, the fewer morphological defects of the composite coatings there are, and the thicker the electroless nickel layer is. The composite coatings prepared by the most hydrophobic self-assembled layer only exhibited N-type semiconductor characteristics, while the other two exhibited P-N dual-semiconductor characteristics. The MAO/SAM/EN three-layer composite coatings provide better protection for the Mg alloy substrate, but as the hydrophobicity of the self-assembled layer increases, the corrosion resistance of the composite coating decreases. The deposition reaction mechanism proves that the hydrophilic film is more conducive to electroless nickel plating. Molecular dynamics simulations show that the E-binding of the three molecules gradually decreases. Both theories agree with the experimental results. (C) 2021 Elsevier B.V. All rights r

关键词： Replacement reaction   Mg-In alloy   Corrosion resistance   Corrosion layer  

摘要： Magnesium alloys play a vital role in future development. However, the application of magnesium alloys with great potential is limited due to their strong corrosion sensitivity. In this work, the double-layer protective film of Mg-In alloy was constructed and adjusted by controlling the amount of indium (In) addition. The cross-section of the corrosion layer presents an inner In-rich layer accompanied by a compact outer layer of magnesium hydroxide with the distribution of Indium hydroxide alternating or interlayer, which significantly enhances the corrosion resistance of the Mg-In alloy and exhibits a self-generated function during the self-corrosion deposition process.

关键词： Graphene oxide   Layered double hydroxides   Micro-arc oxidation   Corrosion resistance   Magnesium alloys  

摘要： The preparation of excellent anti-corrosion coatings is necessary for practical large-scale applications. In this study, a micro-arc oxidation (MAO) coating was prepared on the AZ31 magnesium alloy in advance. Then, on the basis of the MAO coating, the graphene oxide (GO)/MgAl-layered double hydroxide (MgAl-LDH) composite was prepared by hydrothermal chemical transformation in pure GO solution with the mixed oxide of aluminum and magnesium in the MAO coating as the endogenous cation, without introducing any kind of salts. The chemical states, structural composition and morphology of the GO/LDH-MAO coating were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The potentiodynamic polarization revealed that 0.1 GO/LDH-MAO coating (3.89 x 10(-9) A/cm(2)) is more resistant to corrosion than MAO coating (9.89 x 10(-6) A/cm(2)) in 3.5 wt% NaCl solution. The organic combination of Mg-Al LDH and GO can obviously enhance the corrosion protection ability of the coating. This research explored in detail the possible corrosion protection mechanisms regarding GO/LDH-MAO coatings, which supplied the feasibility for enhancing the anti-corrosion performance of MAO coating.

关键词： Magnesium alloy   Friction stir processing   Graded microstructure   Texture   Post-dynamic recrystallization  

摘要： The present work deals with the effect of mechanical post-treatment on the microstructure and texture evolution of friction stir processed Mg-4.37 wt%Y-2.9 wt%RE-0.3 wt%Zr alloy. In this respect, the stir processed specimens were compressed down to engineering strain of 10 and 20%, and the resultant microstructures were characterized. Through applying subsequent compressive loading, fraction of low angle boundaries was increased, substructure was developed, the grain size was refined, and specified misorientation angles/texture components were faded or appeared. The degrees of such evolutions were different between the surface layer and stir zone, and resulted in development of graded microstructures. The fraction of strain-less and fresh grains was considerably decreased;but the fraction of coarse grains holding high grain orientation speared (GOS) was remarkably increased specially by moving away from material surface. Schmid analysis indicated the higher probability of non-basal slip within the unstable coarse grain in the course of subsequent loading. This was led to the occurrence of post-dynamic recrystallization which was traced through the sequence of substructure development and transformation of the low angle boundaries in to the high angle ones. Such gradual microstructure/texture evolution indicate the stir processing plus compression loading as capable method for fabrication of micro-scale functionally graded materials.

关键词： AZ31 magnesium anode   Ultrafine grains   Discharge behaviour   Mg-air battery  

摘要： Fabricating the magnesium alloy with fine grains, low dislocation density, and weak grain orientation is of crucial importance to enhance its anode performance for primary aqueous battery. However, this structure mode can hardly be realized for bulk magnesium alloy via the conventional approaches such as plastic working. Herein, we construct an AZ31 magnesium alloy with ultrafine grains (667.28 +/- 291.35 nm) by using the spark plasma sintering of the alloy powder that has been treated via high-energy ball milling. This alloy exhibits weak grain orientation and its dislocation density is not increased compared to the precursor alloy. Benefiting from the unique microstructure, the modified AZ31 displays significantly more active behaviour with enhanced capacity during the discharge of Mg-air battery, as compared with the precursor AZ31 that has the grain size of 472.89 +/- 154.31 mu m. Furthermore, the impact of ultrafine grains on the discharge behaviour is also analysed based on microstructure characterization and electrochemical response. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： Twinning   Detwinning   Crystal plasticity   Magnesium alloys   AZ31B   Evolutionary algorithm  

摘要： The paper reports experimental and numerical study of different deformation mechanisms activated in the AZ31B magnesium alloy sheet subjected to cyclic in-plane tensile ? compressive deformation. The influence of slip, twinning and detwinning upon the mechanical response and texture evolution of the material is thoroughly investigated. The regime of twinning and detwinning activity is assessed based on the variation of hardening modulus in the course of the process. Velocity-based large strain crystal plasticity model accounting for twinning and detwinning is formulated. The crystal plasticity model parameters are identified using the implementation of the evolutionary algorithm. Predicted activity of deformation mechanisms is discussed with respect to the experimental data.

关键词： ZK60 Mg alloy   Corrosion   Repeated Upsetting (RU)   Mechanical properties   Severe plastic deformation (SPD)  

摘要： The Repeated Upsetting (RU) as a powerful severe plastic deformation technique to produce fine-grained thick plates was investigated in the present research. The evolution of microstructure, texture, mechanical properties, and bio-corrosion behavior of ZK60 Mg alloy after applying 3 and 5 passes of RU process were analyzed in detail. Results showed that performing the RU process on the rolled-annealed ZK60 alloy transformed its initial coarse microstructure with a mean grain size of 40 mu m to a bimodal microstructure after 3rd pass, and a fine equiaxed grain structure having an average size of about 2.8 mu m after 5th pass. The texture of rolled-annealed sample, containing basal components, has been transformed into a shear texture with higher intensity during the RU process. The great improvements of strength after RU were attributed to the finer grain size, while easier activation of basal slip due to the presence of desirable texture component, and uniformly distributed fine second phase particles resulted in larger elongation to fracture. The corrosion resistance of the ZK60 alloy decreased after processing by RU, due to the presence of more non-basal planes in contact with the corrosive solution. Nevertheless, the 3-passed sample can be introduced as a biodegradable Mg alloy for implant applications due to its good combination of acceptable strength, ductility, and corrosion resistance. (C) 2021 Elsevier B.V. All rights reserved.

关键词： ZM1 alloy   Carbon nanotubes(CNTs)   Composites   Microstructure   Mechanical properties  

摘要： Melt processing is a promising process to fabricate Mg-CNTs(carbon nanotubes)composites with high performance and large *** this work,the liquidmixing technique and ball-milling processes as well as the stirring casting method were used to prepare ZM1-1.0 CNTs-L and ZM1-1.0 CNTs-B composites,*** composites were studied using optical microscopy(OM),Raman spectroscopy,scanning electron microscope(SEM),transmission electron microscope(TEM)and room-temperature tensile *** results show that the yield strength(YS),ultimate tensile strength(UTS),elongation and microhardness values of the ***-L composite are improved by 37.3%,29.6%,37.0%and33.3%,respectively,compared with those of ZM1 *** uniform dispersion of CNTs as well as the strong interfacial bonds with the Mg matrix is the main reason for the significant improvement in mechanical properties of the as-cast *** mixing combined with the stirring casting method is favorable to fabricate Mg-CNTs composite with high mechanical properties.

关键词： 介孔二氧化硅   药物载体   生物相容性   口腔医学   应用  

摘要： 近年来,介孔二氧化硅颗粒在分子材料、催化吸附、生物医学等领域的应用越来越受到关注。介孔二氧化硅材料具备粒径、孔径大小可调、骨架结构稳定、空间结构高度有序、表面可修饰、生物相容性好等优势。本文就介孔二氧化硅的基本特性,影响介孔二氧化硅性能的主要因素以及介孔二氧化硅在口腔医学方面的应用进行一综述。

关键词： 铝镁合金   MIG焊   焊接工艺   凝固裂纹   气孔  

摘要： 为研究铝镁合金焊缝内部气孔对不同MIG焊焊缝凝固裂纹敏感性的影响,使用鱼骨型试板测试了8种焊接工艺下的焊缝凝固裂纹长度,并分别对焊缝区的微观气孔进行观察。结果表明:双脉冲MIG焊焊缝凝固裂纹敏感性普遍大于单脉冲MIG焊的,但其焊缝气孔数量却比单脉冲MIG焊的少;双脉冲MIG焊焊缝凝固裂纹敏感性增大的原因是双脉冲电流的振荡作用使气孔聚集,导致气孔内部气压增大,阻碍了低熔点液相向微观热裂纹的填充。