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： Plasma electrolytic oxidation (PEO)   composite coatings   graphene oxide   hydrothermal treatment  

摘要： Graphene oxide (GO) integrated composite coatings were deposited on AZ91 magnesium alloys by the PEO (Plasma Electrolytic Oxidation) and the treatment which has a post-PEO hydrothermal process. For the first group samples, PEO was performed in the silicate/phosphate-based electrolyte including 5-10 mu m in size the GO particles synthesized using the Tour Method. For the second group samples, after PEO treatment, the post-PEO hydrothermal process was carried out in the oven in the GO-distilled water mixture containing GO produced with the same protocol. The effects of GO on wear behavior, structural and morphological features of composite coatings were examined with a pin-on-disc tribometer, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy, respectively. The results showed that the addition of GO improved significantly the adhesion to the substrate material of composite coatings, increased the coating thickness and hardness. Post-PEO hydrothermal process resulted in the formation of partial a thin solid lubricant GO film on the surface of composite coatings and thus exhibited the best wear and friction resistance.

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.

关键词： 镁合金   肝素   耐蚀性能   蒙脱石   生物材料  

摘要： 目的为解决镁合金血管支架使血管内皮化、造成再狭窄等问题,在AZ31镁合金表面制备具有抗凝特性的肝素(HS)/蒙脱石(MMT)复合涂层,并研究其耐蚀性能。方法采用水热法在AZ31镁合金表面制备钠蒙脱石(Na-MMT)涂层,在此基础上通过浸泡法以蒙脱石为载体,制备肝素/蒙脱石复合涂层。利用扫描电子显微镜(SEM)、傅里叶红外光谱仪(FT-IR)、X射线衍射仪(XRD)对所得涂层进行表面分析,通过电化学分析和析氢速率测定研究涂层的耐蚀性。结果表面分析结果显示,通过水热法和浸泡法得到了均匀致密的HS-MMT涂层,厚度为41mm。HS-MMT涂层的EDS元素分析图中出现了N、S及蒙脱石的基本元素,同时该涂层的FT-IR和XRD图出现了肝素及蒙脱石的特征峰。耐蚀性研究显示,与AZ31镁合金相比,HS-MMT涂层的自腐蚀电位升高了0.29 V,腐蚀电流密度降低了2个数量级,且其平均析氢速率为0.016 mL/(cm×h),仅为AZ31镁合金平均析氢速率的18%。结论采用水热法和浸泡法在AZ31镁合金表面成功制备了HS-MMT涂层,该涂层具有良好的耐蚀性能,为镁合金血管支架的研究提供了一种新方案。

关键词： 高强镁合金   高强度镁合金   国防军工   抗蚀性   抗疲劳性能   电学性能   艾利  

摘要： 艾利特超级镁合金(Allite Super Magnesium)是一种高强度镁合金,是美国艾利特公司研发的,过去仅用于国防军工和航空航天领域,现在它的价格有所下降,成为一种高强度的比铝轻得多的价格较为合理的镁合金,开始在其他领域应用。它有三种型号:AE81、ZE62、WE54,各具特色,强度也各异,但都具有高的抗蚀性、抗疲劳性能和耐磨性,还有优秀的硬度和电学性能。