关键词： Graphene nanoplatelets   Magnesium matrix nanocomposites   Interface characteristics   Uniform dispersion  

摘要： Magnesium matrix nanocomposites reinforced with graphene nanoplatelets (GNPs) additives have long been considered as exciting prospects among nanotechnology applications. Here, the thixomolding process, an extremely efficient dispersing technology, was applied to prepare AZ91D magnesium alloy- GNPs nanocomposites with different GNPs contents (0, 0.1, 0.3, 0.6, 0.9 and 1.2 wt%). The effects of screw rotate rate (RS) and injection velocity (VI) on microstructures, GNPs dispersibility and mechanical properties were investigated. The GNPs, fairly uniform dispersion in the nanocomposites, were incorporated in the alpha-Mg grains, not only in the grain boundaries. Strong bonding interfaces between GNPs and alloy matrix were established because of the formed MgO nanoparticles leading to the formation of Mg/MgO semi-coherency interface and MgO/GNPs interface. Compared with other previously reported results, a relatively higher overall efficiency was achieved in the prepared magnesium matrix nanocomposites. The developed technology has a potential for large-scale industrial production of not only thin-walled complex parts, but also thick-walled products such as automobile parts with complex structure.

关键词： Surface treatment   Pr-based nanofilm   AZ31 magnesium alloy   XPS   AFM   Corrosion   PU  

摘要： This study deals with the Mg-AZ31 alloy anticorrosion properties improvement via a novel surface treatment method. In this regard, the praseodymium (Pr)-based film formation on the Mg-alloy surface at different film formation conditions (i.e., pH, time, temperature) were investigated. The composition of the generated Pr-based film on the Mg-AZ31 alloy surface was characterized in depth using atomic/microscopic level techniques, i.e., Xray photoelectron spectroscopy (XPS), atomic force microscope (AFM), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and contact angle (CA) test. The influence of Pr film on the polyurethane (PU) coating adhesion properties and corrosion protection performance were studied by the pull-off test, neutral salt spray (NSS), and electrochemical impedance spectroscopy (EIS) analyses, respectively. FE-SEM micrographs revealed that the metal surface was covered with a Pr film, which has brought about a rough surface. Applying the Pr film to the Mg alloy surface has caused significant improvement in the corrosion resistance characteristics. A 94.84% corrosion retardation potency was recorded for the Pr-modified Mg alloy at the optimum surface chemical treatment condition. A significant improvement in the adhesion degree (about 64%) was obtained for the PU film on the Mg alloy modified by an optimized Pr film. Results have declared that the Pr-based film could improve the Mg alloy corrosion resistance by affecting the anodic/cathodic reactions through the formation of insoluble and electrically insulate inorganic film and enhancing the PU adhesion by providing a surface with high energy/wettability and micro-nano scales roughness.

关键词： Aluminum alloys   Magnesium dopants   Molecular dynamics   Grain boundary segregation   Grain boundary migration   Grain boundary sliding  

摘要： Atomistic simulations have been used to study the grain boundary (GB) migration in pure Al and Mg-doped Al binary alloys. The results of shearing simulations indicate that the effect of dopants on the GB migration depends on the character of the GB. Negligible influence is found on the migration of the coherent n-ary sumation 3 GB and only a slight change was found in its strength due to the doping. For the other GBs considered in our study, GB migration was pinned by dopants at the GBs, which results in a strengthening effect. The atomic-level GB migration mechanisms are identified for both shear-coupled GB migration in pure Al and dopants pinning GB migration in Mg-doped Al alloys.

关键词： Multistage fracturing   Dissolvable magnesium alloy   Sliding wear   Wear mechanisms  

摘要： The mechanical properties and wear performance of a dissolvable magnesium alloy used for manufacturing the temporary downhole fracturing parts were reported in this study. The dissolvable magnesium alloy's wear performance was compared with that of a commercially available 7075 aluminum alloy in dry sliding condition. The wear tests were performed on a universal tribometer at various normal loads ranging from 20 N to 60 N with a sliding velocity of 10 mm/s to simulate the wear between the fracturing tool and the ceramic proppant (Al2O3 particles). Mechanical testing showed that the ultimate tensile strength and compressive strength of the dissolvable magnesium alloy was 275.5 MPa and 482.7 MPa. The wear testing indicated that the dissolvable magnesium alloy exhibited lower friction coefficients, whereas larger wear rates than that of the 7075 aluminum alloy. The worn surface analysis of the tested magnesium alloy revealed that abrasive wear was the dominant wear mechanism, and oxidative wear was observed with the normal load further increased. The obtained results would provide further insights into the dissolvable magnesium alloy and guide the design of temporary structures or parts in certain applications.

关键词： Magnesium alloy   Reinforced concrete   Structural   Corrosion   Surface  

摘要： A new concept of energy-saving design is proposed in this study that magnesium alloys are considered for rebars in concretes due to their lightweight, energy-efficient and environmentally friendly characteristics. Although magnesium alloys have promising physical properties such as high specific-strength and good fracture toughness, their poor corrosion resistance always hampers their wider applications. Therefore, it is urgent to conduct a preliminary corrosion evaluation. In this study, it is found by longterm immersion test and electrochemical corrosion test that AZ80 alloy has an excellent corrosion resistance in simulated concrete pore solution made of saturated Ca(OH)(2) solution. Furthermore, the saturated solution is diluted by pure water and 3.5 wt% NaCl solution, respectively. The unsaturated solution diluted by pure water does not change the anti-corrosion behavior of AZ80 alloy, whereas the corrosion resistance is significantly deteriorated when chloride ions are introduced. SEM observation corroborates that there exists a layer of protective film on the surface after immersion in the simulated concrete pore solution for 30 days and an intervention of chloride ions can induce a catastrophic surface damage. (c) 2020 Elsevier B.V. All rights reserved.

关键词： Magnesium alloy   Corrosion resistance   Physical barrier coating   Smart self-healing coating  

摘要： With promising mechanical properties and biodegradability, magnesium (Mg) and its alloys are considered as potential candidates in both industrial and biomedical fields. However, rapid corrosion is a major obstacle that severely prevents their widespread applications. Surface modification is a costeffective way to prevent the corrosive medium from contacting with Mg substrate. Generally, fabricating a dense and stable coating as a physical barrier can effectively inhibit the corrosion of Mg substrates. However, in some complex service environments, the coatings are inevitable to be damaged during use. In this case, it is essential to equip coatings with smart self-healing abilities. This article reviews recent advances in conventional physical barrier coatings and smart self-healing coatings on Mg alloys for industrial and biomedical applications. For physical barrier coatings, metal-based coatings, metal hydroxides and hydrotalcite coatings, metal oxide coatings, silane sol-gel coatings, polymer coatings, Ca-P coatings, and others like graphene-based coatings are mainly reviewed. For smart selfhealing coatings, chemical conversion coatings, encapsulation coatings, and layer-by-layer assembled coatings are reviewed. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Nickel recycling   Wastewater   Magnesium alloy waste   Galvanic corrosion  

摘要： A process for recycling Ni2+ in Ni-plating wastewater was investigated. This study employed Mg alloy flash waste to reduce the Ni2+ in the wastewater into metallic Ni. Fine second-phase Mg17Al12 in a network is the critical point for promoting the reduction reaction of Ni2+. The microstructures of the Mg alloy flash scrap and the diecast Mg alloy scrap waste fulfilled the requirement. The Mg17Al12 is like a catalyst for the quick reduction of the Ni2+ ions into pure Ni metal. Contrarily, pure Mg (not containing Mg17Al12 particles) and gravity-cast AZ91D Mg alloy (having coarse Mg17Al12 particles) were not suitable for being used for the Ni2+ wastewater treatment. Based on the above results and discussion, using the Mg alloy flash scrap waste for treating the laboratory-made Ni2+-containing wastewater, the wastewater initially with similar to 5600 ppm of Ni2+ ions could be reduced to similar to 20 ppm in 2 h. When applying the Mg alloy flash scrap for the Ni plating wastewater from industry, the concentration of Ni2+ was able to be reduced from-16,670 ppm to-1434 ppm in 10 min for the wastewater at 90 degrees C.

关键词： 半固态   镁合金   内冷搅拌   微观组织  

摘要： 提升镁及其合金强度和室温韧性是扩展镁及其合金应用的关键技术,对镁合金凝固过程半固态处理是改善微观组织、提高产品质量的一个重要工艺途径。因此,本文提出内冷搅拌法制备非枝晶AZ系镁合金半固态浆料,采用快速淬火研究内冷搅拌过程AZ系镁合金半固态浆料初生相演变规律。通过观察金相微观组织发现,在金属熔体与平衡体质量比为3:1、平衡体温度为室温、熔体温度高于液相线20oC时,随着平衡体旋转速度增加,熔体整体温度梯度减小,凝固组织从粗大枝晶逐渐变为细小近球晶;随着旋转平衡体搅拌时间延长,浆料组织分散变得均匀,后续由于晶粒生长,晶粒出现团聚;Al元素含量增加能够细化自然凝固初生相α-Mg,而内冷搅拌法对AZ系镁合金半固态处理发现,Al元素含量虽然一定程度上细化初生相α-Mg,随着内冷搅拌条件引入,Al元素含量增加细化程度较小,而内冷搅拌条件是细化初生相α-Mg的主要因素。

关键词： 铸造镁合金   疲劳性能   疲劳裂纹   强化方法  

摘要： 归纳了典型铸造镁合金的疲劳强度和疲劳寿命研究现状,介绍了铸造镁合金疲劳裂纹的萌生及扩展机制,以及基体组织、晶粒尺寸、第二相、铸造缺陷和工作环境等多种因素对镁合金疲劳性能的影响规律,总结了提高镁合金疲劳性能的方法,最后对铸造镁合金疲劳方面的研究进行了展望。

关键词： Corrosion   Metals and Alloys   Microstructure   XPS   Surfaces   Thin films  

摘要： In order to give the capability of cathodic protection to silane conversion coating (SCC), nano-Mg particles was used to modify SCC, and a nano-Mg modified SCC (nano-Mg@SCC) was prepared on magnesium alloy (MA) AZ91D. The microstructure and anti-corrosion of nano-Mg@SCC were characterized. Both Si-O-Mg and Si-O-Si bonds were mainly responsible for constructing the nano-Mg@SCC/AZ91D system: the former bond acted at the interfaces between nano-Mg particles and SCC as well as between nano-Mg@SCC and AZ91D substrate, and the latter bond acted in the interior of nano-Mg@SCC. The corrosion current density (i(c)) and the coating resistance (R-c) for the nano-Mg@SCC coated AZ91D were respectively lower and higher than those for the single-SCC coated AZ91D;at the same time, both stable open circuit potential (OCP) and corrosion potential (E-c) of nano-Mg@SCC coated AZ91D were more negative than those of bare AZ91D. The nano-Mg@SCC retained the original capability of physical barrier and possessed the new capability of cathodic protection, so nano-Mg@SCC provided better corrosion resistance to AZ91D substrate than single-SCC did. (c) 2020 Elsevier B.V. All rights reserved.