关键词： Rib-web component   Isothermal local loading forming   Loading modes   Filling rate   Magnesium alloy  

摘要： The lightweight of aerospace equipment has urgent demand for the large-scale reinforced wall structure with higher strength and toughness. In this research, the isothermal local loading forming (ILLF) process was proposed to decrease the extremely larger forming load and promote the material filling at rib locations. A typical rib-web component with two cross ribs was investigated and the experiment setup was designed to fabricate it under three loading modes (two new local loading modes and one conventional integral loading mode). The parallel finite element (FE) models were established and verified by comparing the experimental points and simulation curve. The material filling effect and forming load were compared under three loading mode, and the Lode parameter together with hydrostatic pressure was applied to analyze these differences during the deformation processes. Based on the principle of more uniform equivalent strain and larger filling rate, the best loading mode was determined and its corresponding process parameters were optimized.

关键词： Metals and alloys: AZ31-0.5Ca alloy   Superplasticity   Microstructure   (Mg,Al)(2)Ca particles  

摘要： In this short communication, the superplasticity of AZ31-0.5Ca Mg alloy was investigated and was compared to that of the Ca-free counterpart (AZ31 Mg alloy). For this purpose, AZ31 and AZ31-0.5Ca Mg alloy samples were subjected to elevated temperature tensile tests at various strain rates. The results reported in this work showed that the Ca addition lead to a higher superplasticity (similar to 320%) at strain rate and temperature of 0.001 s(-1) and 300 degrees C, respectively, as compared to that observed in the Ca-free AZ31 alloy.

关键词： Polythiophene   corrosion   AZ91A   interfacial interaction   adhesion   coatings  

摘要： The silane functionalized MnO2 nanoparticles were incorporated in polythiophene (PT) to produce PT/silanes/MnO2 nanocomposites. The surfaces of MnO2 nanoparticles were modified with ethyltrimethoxysilane (ETMS), 3-glycidyloxypropyltrimethoxysilane (GPTMS), and 3-aminopropyltrimethoxysilane (APTMS) and characterized by X-ray diffraction (XRD) studies. The corrosion resistance of newly synthesized PT, PT-ETMS/MnO2, PT-GPTMS/MnO2, and PT-APTMS/MnO2 composite coatings of magnesium alloy (AZ91A) was evaluated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) studies, and scanning electrochemical microscopy (SECM) immersed in natural seawater for several days. The PT-APTMS/MnO2 nanocomposite coatings showed an excellent resistance against corrosion with a charge transfer resistance of over 7517.85 k omega cm(2), which were higher than that of the PT coating (548.25 k omega cm(2)) after 80 days immersion in seawater. The coating with MnO2 nanoparticles modified by APTMS, GPTMS, and ETMS groups showed no significant penetration by corrosive ions during 80 days' immersion due to the strong chemical bonding between amino/epoxide/ethyl groups on MnO2 and the sulfur of PT. Decreased current was detected at the scratch of investigated nanocomposite coatings by SECM analysis. The affinity between PT and silanes/MnO2 nanoparticles is enhanced due to their interfacial interactions, which improves the dispersion of silane functionalized MnO2 nanoparticles in PT to produce uniform coatings. Scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) and XRD technique of synthesized nanocomposite coatings confirmed the presence of corrosion products which block the dissolution of Mg alloy. Excellent mechanical properties are shown by the investigated coatings.

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： 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： 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： 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.