Eigenschaften verschiedener Kontaktwerkstoffe für Schaltgeräte der elektrischen Energietechnik und deren Gefügeänderungen durch Lichtbogenbelastung

Properties of Different Contact Materials for Electrical Switchgear and Changes in Structure due to Arcing . Due to arcing during switching operations the microstructure of the material below the contact surface is converted. After the contacts have been used in switching their properties are determined to a great extent by the contact microstructure so formed. By means of a test switching apparatus the contact properties of the materials pure copper and pure silver produced by melting and of AgNi 10, W Ag 35 NiCuT, AgCdO 12 and AgC 3 produced by powder metallurgy were investigated during making operations and alternating making and breaking. Microsections from the used contacts were prepared perpendicular to the contact surface to evaluate the contact microstructure. Considerable differences occur in the contact microstructure depending on the type of material and switching. The contact properties welding force, contact erosion and contact resistance are affected so much by the breaking operation that it can result in a reversal of the tables of materials. In selecting a contact material with a test switching apparatus for use in a specific type of switchgear the contact properties must therefore be acquired simultaneously as a measurement series during test conditions related to the application.     

A review on ultrasonic spot welding of copper alloys

As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided.     

Mechanical analysis of ultrasonic welding considering knurl pattern of sonotrode tip

Ultrasonic welding is attracting increasing attention in dissimilar material joining. The knurl pattern of sonotrode tip strongly affects the contact status and friction coefficient at the sonotrode/workpiece interface and thus plays a significant role on joint formation. Finite element models, with/without consideration of geometrical feature of sonotrode tip, were constructed to reveal the role of sonotrode geometry during ultrasonic welding process of copper to aluminum. The coupled thermal–mechanical fields and high-strain-rate deformation of metallic materials were incorporated in the models. The simulated results showed that the serrated knurl pattern of sonotrode tip greatly influenced the in-process variables (including stress, strain and displacement) at the contact surfaces of specimens. The localized concentration of plastic strain caused by the specific design of serrated tip knurl pattern, turned out to be the major cause for joint formation. Based on the evolution of average state variables in the bond area, ultrasonic welding process could be divided into three periods. Specimen deformation and material flow mainly occurred in the initial period of welding process. The simulated results were further verified by comparing specimen deformation and temperature evolution with experimental results.     

Wetting of Cu by Bi–Ag based alloys with Sn and Zn additions

Contact angles on copper substrate of Bi–Ag–Sn and Bi–Ag–Zn ternary alloys containing 3, 6, and 9 at.% of Sn and Zn, respectively, were studied with the sessile drop method. Wetting tests were carried out at 573 and 603 K with or without the use of a flux. Without the flux, the examined alloys do not wet copper, i.e., the observed contact angles are higher than 90°. However, in the presence of the flux wetting of copper is observed. In the case of alloys with Sn, the contact angles decrease with increasing content of Sn, while in the case of alloys with Zn no such tendency is observed. Solidified solder–substrate couples were cross-sectioned and examined with scanning electron microscopy coupled with electron dispersive X-ray analysis.     

Correlation Between Chemical Composition of Silver Alloys and Photothermal Radiometry Signals

The development of nondestructive and noncontact techniques for evaluation of metallic materials is invaluable to metal characterization. The photothermal radiometry (PTR) amplitude and phase images of silver alloys were used to study the silver distribution in alloys rich in silver and copper for Ag concentrations between 37?mass% and 92?mass%. The silver concentration was determined using inductively coupled plasma. It was found that for Ag concentrations lower than 50?mass%, the PRT signals are governed by the thermal and optical properties of copper and vice versa. It was possible to establish a good correlation between the PTR amplitude and phase signal with the Ag concentration. This means that after calibration it is possible to determine the Ag concentration using nondestructive evaluation.     

Relationship between base metal properties and friction stir welding process parameters

Friction stir welding (FSW) is a solid state welding process for joining aluminum alloys and has been employed in aerospace, rail, automotive and marine industries for joining aluminium, magnesium, zinc and copper alloys. In FSW, the base metal properties such as yield strength, ductility and hardness control the plastic flow of the material under the action of rotating non-consumable tool. The FSW process parameters such as tool rotational speed, welding speed, axial force, etc. play a major role in deciding the weld quality. In this investigation, an attempt has been made to establish relationship between the base material properties and FSW process parameters. FSW joints have been made using five different grades of aluminium alloys (AA1050, AA6061, AA2024, AA7039 and AA7075) using different combinations of process parameters. Macrostructural analysis has been done to check the weld quality (defective or defect free). Empirical relationships have been established between base metal properties and tool rotational speed and welding speed, respectively. The developed empirical relationships can be effectively used to predict the FSW process parameters to fabricate defect free welds.     

Fortschritte der Kontaktwerkstoffentwicklung

Progress in Contact Material Technology . Materials for electrical contacts have to show a plurality of different properties which in most cases cannot be found with pure metals. The development of new and better contact materials is therefore restricted to alloys and mostly to composite materials. The use of intermetallic compounds and ordered alloys will be described. This type of materials shows better corrosion behaviour, lower are erosion and lower material transfer. Silver-, gold- and platinumbased dispersion hardened alloys and methods of manufacture will be described. Today there are tendencies for the use of fiber reinforced metals as materials for electrical contacts. Some applications will be discussed.     

Low-current resistance spot welding of pure copper using silver oxide paste

Silver oxide particles were used as an insert material to reduce the current necessary for resistance spot welding of pure copper plates. To form a conduction path for successful bonding, silver-oxide particles were reduced before bonding by preheating with a reducing solvent at 120 °C for 3 min to cover the particles with silver nanoparticles. At 2200 A, bonding could be achieved with silver-oxide particles, whereas bonding was not successful in welding experiments conducted without insert materials or with fine silver particles. Bonding was accomplished through the formation of a dense sintered layer. When such silver oxide particles are used for resistance spot welding, the joining is achieved by the high sinterability of the generated silver nanoparticles.     

The treasure of gold and silver artifacts from the Royal Tombs of Sipán, Peru — a study on the Moche metalworking techniques

In 1987–1990, a spectacular treasure of gold and silver ornamental and ceremonial artifacts was recovered scientifically from the unlooted Royal Tombs of Sipán, Peru (dated to approximately AD 50–300). These objects give evidence of the outstanding craftsmanship of the Moche metalsmiths and reflect the various elaborate metalworking techniques available at that time. The present paper summarizes the results of a study on an array of artifacts stemming mainly from the tomb of the “Lord of Sipán.” Most of the objects were found to be made of thin sheet metal (1–<0.1 mm thick), which was further worked by cutting, embossing, punching, and chasing. Three-dimensional structures were created from pieces of the sheet metal by mechanical or metallurgical joining (soldering or welding). The Moche metalsmiths were masters in making objects that looked like pure gold or silver. In the case of copper objects, the surfaces were often found to be gilded electrochemically by the deposition of very thin gold films. In the case of objects made of alloys of copper with gold and some silver (tumbaga) or of copper with silver, the surface gilding or silvering was achieved by the depletion of copper, mostly by selectively oxidizing the surface copper and etching away the copper oxides that are formed.     

Effects of bimetallic nanoparticles on seed germination frequency and biochemical characterisation of Eruca sativa

In the modern era of science and technology, nanotechnology is becoming popular science field because materials at nanoscale contain improved physical, chemical and biological properties. This study aimed to explore the capacity of bimetallic nanoparticle alloys of silver (Ag), copper (Cu), gold (Au) in different ratios to evaluate the effects on medicinally important plant Eruca sativa. Biochemical parameters of Eruca sativa were studied by applying bimetallic alloy nanoparticles. Seeds of Eruca sativa were germinated on Murashige and Skoog medium with various combinations of nanoparticles suspension employed in concentration of (30 µg/ml). Bimetallic alloys were considered as a stress inducing factor in plants while studying the phytotoxicity. Many secondary metabolites were released because defensive mechanism of plants was active in response to stress. Such secondary metabolites produced in medicinal plants have a great capability in treating the human diseases. In the authors’ study, nanoparticles of small size and of high toxicity effect produced more secondary metabolites like total protein content, total flavonoids and total phenolic content.Inspec keywords: botany, biochemistry, nanoparticles, silver alloys, copper alloys, gold alloys, biomedical materials, nanomedicineOther keywords: seed germination frequency, Eruca sativa biochemical characterisation, nanotechnology, bimetallic nanoparticle alloy, silver alloy, copper alloy, gold alloy, murashige, skoog medium, nanoparticles suspension, secondary metabolite, medicinal plant, human disease, total protein content, total flavonoid, total phenolic content, Au, Ag, Cu     

铝合金线性摩擦焊研究现状

线性摩擦焊作为一种新型的固相焊接技术,热输入低、焊接应力小,适合于铝合金的焊接。介绍了线性摩擦焊的工作原理,主要综述了铝合金线性摩擦焊数值模拟、微观组织和力学性能等3个方面的研究进展。在此基础上,着重介绍了摩擦压力、焊接时间及振动频率等工艺参数对铝合金线性摩擦焊微观组织和力学性能的影响,介绍了工艺参数对铝合金与不锈钢、纯铜、镁合金等异种金属线性摩擦焊微观组织、力学性能及金属间化合物种类和分布的影响。最后,对铝合金线性摩擦焊在数值模拟、接头性能及金属间化合物调控方面存在的不足进行了总结,并对其主要发展方向进行了展望。     

Establishing relationship between the base metal properties and friction stir welding process parameters of cast aluminium alloys

In friction stir welding (FSW), the material under the rotating action of non-consumable tool has to be stirred properly to get defect free welds in turn it will improve the strength of the welded joints. The welding conditions and parameters are differing based on the mechanical properties of base materials such as tensile strength, ductility and hardness which control the plastic deformation during friction stir welding. The FSW process parameters such as tool rotation speed, welding speed and axial force, etc. play a major role in deciding the weld quality. FSW Joints of cast aluminium alloys A319, A356, and A413 were made by varying the FSW process parameters and the optimum values were obtained. In this investigation, empirical relationships are established and they can be effectively used to predict the optimum FSW process parameters to fabricate defect free joints with high tensile strength from the known base metal properties of cast aluminium alloys.     

Al-Cu双金属复合结构的扩散连接试验研究

应用扩散连方法进行了Al-Cu双金属复合结构的试验研究，比较了不同的焊接工艺，材料组合以及母材状态情况Al合金与Cu的连接性，观察了接头区域的微观组织结构，研究表明，固相扩散连接是一种适用于异种材料连接的有效方法，通过在连接区域形成Al-Cu金属间化合物，达到Al和Cu的有效连接，材料组合，母材原始状态以及连接工艺参数对Al合金与Cu的扩散连接存在着明显的影响。表面镀Ni工艺不但能够有效阻止Al和Cu之间形成脆性相，而且Al和Ni之间形成了良好的扩散连接，改善了接头性能。     

Effect of ultrasonic welding parameters on microstructure and mechanical properties of dissimilar joints

Ultrasonic spot welding has received significant attention during past few years due to their suitable applications in comparison to conventional fusion welding techniques. Fusion welding of dissimilar Aluminum and Stainless steel alloys is always a challenging task because of poor control on grain size and formation of undesirable brittle intermetallic compounds in the weld metal, which have deleterious effect on mechanical properties. In the past, welding of dissimilar alloys has been performed using electron beam welding, laser beam welding and friction stir spot welding, resistance spot welding, etc. However, little work has been reported on dissimilar welding of Aluminum and Stainless steel alloys using ultrasonic spot welding. The objective of the present work is to optimize ultrasonic spot welding parameters for joining 3003 Aluminum alloy with 304 Stainless steel. Welding was performed at various clamping pressures (i.e. 30, 40, 50 and 60 psi) and energy levels for investigating its effect on microstructure, mechanical properties and bond quality of the weld. Different levels of weld quality i.e. ‘under weld’, ‘good weld’ and ‘overweld’ were identified at various welding parameters using physical attributes. The weld specimens prepared with energy 125 and 150 J showed the maximum bond strength and were rated as “good” weld. It was also revealed that for a good quality weld, the maximum tensile strength is achieved once a reasonable amount of bond density and material thinning (required for the formation of metallurgical bonds) is attained.     

形变铜基原位复合材料的研究现状及展望

高强高导铜合金是一类具有优良综合物理性能和力学性能的结构功能材料,形变铜基原位复合材料是高强高导铜合金的研究热点和发展方向之一,其突出的特点是具有超高的强度和良好的电导率.综述了形变铜基原位复合材料的国内外研究现状,并指出这类材料的发展方向为高性能Cu-Fe系原位复合材料的开发以及材料的工业规模制备和应用.     

先进航空材料焊接过程热裂纹研究进展

高焊接热裂纹敏感性是制约新一代合金材料在航空航天领域推广应用的技术瓶颈。本文分别从焊接热裂纹的产生机理和各类合金裂纹敏感性实验的角度梳理该方向的研究进展。焊接热裂纹主要包括凝固裂纹（在焊缝内部产生）和液化裂纹（在焊缝与部分熔化区交界处产生）。影响焊接热裂纹产生的因素包括材料成分、焊接热循环以及接头热应力。在梳理焊接热裂纹机理研究的基础上,分别总结了铝合金、镁合金、先进高强钢以及镍基合金焊接热裂纹的实验研究进展。建立考虑复杂多组元以及结晶形态对裂纹敏感性影响的量化判据,是该领域未来的重要发展方向。针对母材和焊材进行成分优化、添加形核剂或实施辅助工艺措施,是工程应用领域抑制热裂纹缺陷的有效方法。开展焊接热裂纹产生机理及其抑制方法研究,有助于突破新一代合金材料加工技术瓶颈,推进其在航空航天领域的应用。     

Wettability and contact interaction of gallium-containing melts with non-metallic solids

The wettability of sapphire, quartz and graphite by gallium, gallium-based binary alloys with indium, tin, copper, silver, nickel, manganese, chromium, vanadium and titanium and by ternary Cu-Ga-Ti, Cu-Ga-Cr and Cu-Ga-Mn alloys has been studied by sessile drop, plate weight and meniscus form methods. The character and intensity of contact reactions and the composition of transition layers at the solid—melt boundary have been investigated by X-ray analysis and profilographic measurements and the correlation between the wettability and the contact reaction intensity has been established. The condition for high wettability of non-metallic solids by multicomponent melts is shown to be a combination of high affinity of a component for solid phase atoms with high thermodynamical activity of this component in the melt.     

Rapid penetration of bismuth from solid Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> along grain boundaries in Cu and Cu-based alloys

As well known, bismuth rapidly penetrates into copper grain boundaries at about 550 °C and embrittles copper. In the experiments, the authors have used solid Bi₂Te₃ for the embrittlement of pure copper and copper-based solid solutions containing iron and silver. The investigated alloys were heated in the closed volume together with Bi₂Te₃ for a short time (5–90 min) at 570 °C in the hydrogen atmosphere. Bi₂Te₃ did not contact with copper samples during annealing. After that, the samples were bent and grain boundary cracks were formed (with the depth about 10–500 μm). Experiment showed that silver accelerates the embrittlement in the contrast to iron. The cracks in the silver–copper alloys were deeper than in the iron–copper ones. It was assumed that the depth of cracks is equal to the penetration depth. The reasons for this phenomenon were discussed in terms of the impurities effect on the grain boundary segregation.     

Microstructure and properties of the laser butt welded 1.5-mm thick T2 copper joint achieved at high welding speed

Laser welding of highly reflective materials, such as copper, has suffered problems such as spatter, underfill and undercut for a long time. This work analyzed the associated mechanism and suggested that appearance and integrity of laser welded copper joint could be improved by conducting the welding process at a high welding speed which is slightly below the critical welding speed for full-penetration welding at the specified laser power. The microstructure, mechanical properties and electrical conductivity of the T2 copper joint achieved under high welding speed were tested. Results show that copper joint and base material (BM) have similar electrical conductivity, the weld fusion zone (FZ) and the heat affected zone (HAZ) are softened; the tensile strength and elongation of the joint are approximately 20% and 84% below those of the BM respectively. The joint breaks near the interface between the longitudinal columnar grain structures (LC) growing along welding direction at the FZ center, and the horizontal columnar grain structures (HC) growing perpendicular to the welding direction at other area of FZ. Degradation of the mechanical properties of copper joint is attributed to the softening of the heated zone and the big angle between the growth directions of LC and HC.     

Improved contacting by the use of silver in solid oxide fuel cells up to an operating temperature of 800 °C

In the following, a contacting variant for solid oxide fuel cells will be presented in which the conductivity of the interconnect is ensured by contact elements made of fine silver. To this end, the interconnect has holes through which the contact elements of fine silver (99.9 wt% Ag) are introduced and then pressed. This pressing process and the thermal expansion of the silver during heating leads to a gastight joint. The silver penetrations are additionally soldered to render them capable of withstanding temperature cycling. Contact resistance measurements and corrosion studies at 800 °C in air or Ar/4 vol.% H₂/3 vol.% H₂O demonstrate the functionality of the contacting variant under the described conditions. The experimental results indicate that contacting by means of silver contact elements ensures long-term stability up to operating temperatures of 800 °C. Current transmission via the silver contact elements means that a large number of materials are conceivable as the interconnect material. In the following application, an FeCrAl steel (1.4767, Aluchrom Y Hf—trade name Krupp Thyssen Nirosta) with 5.7 wt.% aluminium was used. At the operating temperature, a dense aluminium oxide layer forms on its surface which prevents the vaporization, for example of chromium oxide species, during fuel cell operation.