Wear and Corrosion Resistance of AlSi10Mg–CP–Ti Metal–Metal Composite Materials Produced by Electro-Sinter-Forging

Metal–metal composites are a class of composite materials studied for their high ductility and strength, but their potential applications are currently limited by the complex manufacturing processes involved. Electro-sinter-forging (ESF) is a single-pulse electro discharge sintering technique that proved its effectiveness in the rapid sintering of several metals, alloys, and composites. Previous studies proved the processability of Ti and AlSi10Mg by ESF to produce metal–metal composites and defined a correlation between microstructure and processing parameters. This paper presents the wear and corrosion characterizations of two metal–metal composites obtained via ESF with the following compositions: 20% Ti/80% AlSi10Mg and 20% AlSi10Mg/80% Ti. The two materials showed complementary resistance to wear and corrosion. A higher fraction of AlSi10Mg is responsible for forming a protective tribolayer in dry-sliding conditions, while a higher fraction of Titanium confers improved corrosion resistance due to its higher corrosion potential.     

Effect of Heat Treatment on Microstructure and Selective Corrosion of LPBF-AlSi10Mg by Means of SKPFM and Exo-Electron Emission

The paper deals with the evolution of the microstructure of AlSi10Mg alloy obtained by laser powder bed fusion (LPBF), as a function of the post-processing heat treatment temperature. This was approached by complementary methods including FE-scanning electron microscopy, scanning Kelvin probe force microscopy and exo-electron emission techniques. The fast cooling rate of the LPBF process as compared to traditional casting produces a very fine microstructure with high mechanical properties and corrosion resistance. However, the LPBF-AlSi10Mg alloy can be susceptible to selective corrosion at the edge of the melt pools generated by the laser scan tracks. Post-process thermal treatments of the Al alloy induce a marked modification of the silicon network at melt pool edges, in particular at high temperature such as 400 °C. It was found that this is associated to a more homogeneous distribution of Volta potential. Analysis of exo-electron emission confirms the silicon diffusion during thermal treatment. The modification of the silicon network structure of the LPBF-AlSi10Mg during thermal treatment reduces the susceptibility to selective corrosion.     

0～3岁儿童全血微量元素的检测及意义

目的检测了解0～3岁健康儿童全血铜、锌、钙、镁、铁5种微量元素水平,为制订儿童营养膳食结构及健康检查提供指导和参考。方法采用原子吸收光谱法测定2 000例0～3岁儿童全血中铜、锌、钙、镁、铁5种微量元素并对检测结果进行分析。结果 0～3岁儿童分为三组,三组儿童同种微量元素比较水平差异无统计学意义（P〉0.05）,其中锌缺乏率为54.75%,铁缺乏率为23.55%,铜缺乏率为0.8%,钙缺乏率为0.45%,镁缺乏率为0.1%。结论 0～3岁儿童全血中锌和铁缺乏较为严重,铜、钙、镁缺乏较低,建议加大宣传力度,调整饮食结构,重视儿童健康发育,定期健康体检,争取做到早发现、早预防、早治疗,保障儿童健康成长。     

Novel properties of the depolarization-induced endogenous sodium conductance in the Xenopus laevis oocyte

 It has been shown by means of the two-microelectrode voltage-clamp technique that in membranes of Xenopus laevis oocytes a Na⁺-selective permeability can be activated by long-lasting or repetitive depolarization (R.T. Kado and C. Baud, Journal of Physiology, Paris, 77:1113–1117, 1981). In this study the permeability in inside-out giant membrane patches with diameters of 20–30 μm was analysed. Once induced, the Na⁺ permeability has a voltage-dependent open probability that increases with positive potentials and half-maximally activates at about 0 mV. Sudden changes of membrane potential elicit transient currents with strongly voltage-dependent time constants of from less than 1 ms at –150 mV to several hundreds of milliseconds at positive potentials. In contrast to the on-cell configuration, the permeability ceases completely within a few minutes in the cell-free inside-out configuration. This rundown can be prevented by including MgATP, but not Mg²⁺ or ATP alone, in the intracellular solution. Intracellular Mg²⁺ ions, in addition to being a co-factor for ATP in the activation process, decrease the permeability in a dose-dependent manner. Steady-state fluctuation analysis gave no evidence that an increased noise level is caused by open–close kinetics of an ion channel, suggesting that the single-channel conductance is below 1 pS if a channel-like structure is the origin of the endogenous Na⁺ permeability. Received: 14 July 1998 / Received after revision: 4 November 1998 / Accepted: 18 January 1999     

纤维级Mg（OH）2超细粉的应用

天然水镁石经特殊加工制成纤维级Mg(OH) 2 超细粉 ,采用X射线衍射和扫描电子显微分析技术对其结构进行认定和分析 ,研究了它与LDPE、PVC及橡胶等复合后的阻燃作用和相容性 ,同时对共混材料的其他性能进行了分析     

兔脑缺血后脑细胞线粒体Ca^2＋,Mg^2＋的变化

Ｃａ２＋和Ｍｇ２＋是一对相关的阳离子，它们在脑缺血的病理生理变化中起着重要作用。本试验通过对兔脑缺血后脑细胞线粒体Ｃａ２＋、Ｍｇ２＋的测定，发现缺血早期线粒体Ｃａ２＋明显增高而Ｍｇ２＋明显下降，结果提示Ｍｇ２＋／Ｃａ２＋比值下降在缺血性脑损害中具有重要意义。     

Mg2+快速抑制谷氨酸诱导大鼠海马神经元内游离钙浓度升高的作用及特征

目的　采用钙离子特异性荧光指示剂Fura 2 /AM ,使用光电联合检测系统检测镁离子 (Mg2 + )对谷氨酸培养的海马神经元内游离钙离子浓度 ([Ca2 + ]i)的影响和特征。方法　实验设计分三组 (n =2 6 ) ,向细胞吹药各 2 0秒 :①组 1× 10 -5mol/L谷氨酸 ;②组同时 1× 10 -5mol/L谷氨酸和 1× 10 -5mol/LMg2 + ;③组即在②组回到基线后给 1× 10 -5mol/L谷氨酸。结果　①组 [Ca2 + ]i 明显升高 ;②组 [Ca2 + ]I 的变化明显变小 ,其峰值明显下降 ,且Phase 1上升速度减慢 ,Phase 2的时间也有所缩短 ,二相之间的平台期相对延长 ;③组出现与①组中相似的钙震荡表现 ,但Phase 1和Phase 2的时间均缩短 ,△ [Ca2 + ]i 的变化稍低。结论　Mg2 + 可快速抑制谷氨酸诱导大鼠海马神经元内游离钙浓度升高。     

Sensitivity to H, Li and Mg ions of the slow inward sodium current in frog atrial fibres.

Membrane currents have beenmeasured in frog atrial fibres under voltage clamp conditions (double sucrose gap method); the effects on these currents of (i) an increase in [H]_o, (ii) the complete substitution of external Na by Li, (iii) the addition of Mg have been studied.The TTX-sensitive rapid inward current is decreased in acid Ringer (pH 5.6) as compared to values in normal Ringer (pH 7.8); it is unchanged in Li-Ringer and increased in Mg-Ringer. The slow inward calcium current (measured in TTX, Na-free solution) is decreased in acid Ringer and in Mg-Ringer and is unchanged in Li-Ringer. Increases or decreases affecting the rapid sodium current and the calcium current never exceed 40% and are generally smaller. On the other hand the slow inward sodium current (measured in TTX, Ca-free solution) is always suppressed in the three conditions studied.The participation of Na ions to the slow inward current in so called normal Ringer, that is in Mg-free Ringer is discussed. Indirect evidences are presented in favour of such a participation. After addition of Mg 1.8 mm to Ringer the slow inward current is carried only by Ca ions. Since the slow inward sodium current increases markedly in Mg-free Ca-free Ringer, it is concluded that the slow Na conductance is controlled by both Ca and Mg ions in addition to being strongly pH-dependent. It is also suggested that Na and Ca ions participating to the slow inward current do not penetrate necessarily through the same channel.     

Microstructure and Properties of a Graphene Reinforced Cu–Cr–Mg Composite

To improve the graphene/copper interfacial bonding and the strength of the copper matrix, Cu–Cr–Mg alloy powder and graphene nanosheets (GNPs) have been used as raw materials in the preparation of a layered graphene/Cu–Cr–Mg composite through high-energy ball-milling and fast hot-pressing sintering. The microstructure of the composite after sintering, as well as the effect of graphene on the mechanical properties and conductivity of the composite, are also studied. The results show that the tensile strength of the composite material reached a value of 349 MPa, which is 46% higher than that of the copper matrix, and the reinforcement efficiency of graphene is as large as 136. Furthermore, the electrical conductivity of the composite material was 81.6% IACS, which is only 0.90% IACS lower than that of the copper matrix. The Cr and Mg elements are found to diffuse to the interface of the graphene/copper composite during sintering, and finely dispersed chromium carbide particles are found to significantly improve the interfacial bonding strength of the composite. Thus, graphene could effectively improve the mechanical properties of the composite while maintaining a high electrical conductivity.     

Investigation of Surface Integrity of Selective Laser Melting Additively Manufactured AlSi10Mg Alloy under Ultrasonic Elliptical Vibration-Assisted Ultra-Precision Cutting

Additive manufacturing technology has been widely used in aviation, aerospace, automobiles and other fields due to the fact that near-net-shaped components with unprecedented geometric freedom can be fabricated. Additively manufactured aluminum alloy has received a lot of attention, due to its excellent material properties. However, the finished surface of additively manufactured aluminum alloy with nanoscale surface roughness is quite challenging and rarely addressed. In this paper, a novel machining technology known as ultrasonic elliptical vibration-assisted cutting (UEVC) was adopted to suppress the generation of cracks, improve the surface integrity and reduce tool wear during the ultra-precision machining of selective laser melting (SLM) additively manufactured AlSi10Mg alloy. The experimental results revealed that, in the conventional cutting (CC) process, surface defects, such as particles, pores and grooves, appeared on the machined surface, and the machined surface rapidly deteriorated with the increase in cumulative cutting area. In contrast, an almost flawless machined surface was obtained in the UEVC process, and its roughness value was less than 10 nm. Moreover, the tool wear of the CC tool was remarkably greater than that of the UEVC tool, and the standard flank wear width of the CC tool was more than twice that of the UEVC tool. Therefore, the UEVC technology is considered to be a feasible method for the ultra-precision machining of SLM additively manufactured AlSi10Mg alloy.