铝基粉芯线材电弧喷涂工艺参数优化研究

为了使铝基粉芯线材电弧喷涂涂层获得优良的涂层性能,选择涂层孔隙率为判据,通过正交试验和OLYC IA m3金相图像分析系统对铝基粉芯线材电弧喷涂工艺进行了优化,同时采用SprayW atch热喷涂监控系统对喷涂过程中粒子的飞行速度和温度进行了测定.经研究得到了铝基粉芯丝材电弧喷涂的最佳工艺参数.结果表明,影响铝基涂层致密性的工艺因素按主次顺序分别为喷涂气压、喷涂电压和喷涂距离;在所选试验范围内,随气体压力和喷涂电压的增大、喷涂距离的减小,涂层的孔隙率降低;在优化的喷涂工艺参数条件下,铝基涂层最小孔隙率可达1.3%.     

电弧熔丝增材制造铝合金研究进展EI北大核心CSCD

电弧增材制造因其独特的无模壳快速近净成形特点而备受关注,有望成为突破铝合金材料研发与工业应用瓶颈的先进制造技术。电弧增材技术在传统电弧焊接的基础上发展而来,二者均以高能电弧为热源、以金属丝材为原材料进行成形。本文综合分析了电弧增材制造工艺与设备研发现状、凝固与固态相变特性、显微组织特点、冶金缺陷概况以及力学性能特点,论述了热丝及多丝增材制造技术前景和电弧增材制造独特的成形方式与相变显微组织特征。针对电弧增材制造铝合金制造精度及稳定性较差、气孔及热裂缺陷严重、材料力学性能优势不突出的问题,提出了电弧增材制造专用设备开发、熔丝累加快速凝固冶金缺陷控制专用方法研发、专用材料成分及显微组织设计、专用热处理工艺制定等发展方向,为加快电弧增材制造铝合金高端化、定制化、专属化发展提供重要参考。     

自动化高速电弧喷涂锌铝基防腐涂层的耐蚀性研究

采用自动化高速电弧喷涂技术制备出Zn-Al及Zn-Al-Mg-RE涂层。通过浸泡实验考察涂层在3.5%NaCl溶液中的腐蚀行为,并结合扫描电镜(SEM)和X射线衍射仪(XRD)分析涂层的显微组织和相结构变化。结果表明,自动化高速电弧喷涂法制备的涂层均匀,与基体结合良好。浸泡试验两种锌基涂层均未出现红锈,能够对钢结构提供有效保护。     

Experimental observation of rainbow scattering by a coated cylinder: twin primary rainbows and thin-film interference

We experimentally examine the primary rainbow created by the illumination of a coated cylinder. We present a simple technique for varying the coating thickness over a wide range of values, and we see evidence for two different scattering regimes. In one, where the coating thickness is large, twin rainbows are produced. In the second, where the coating is thin enough to act as a thin film, a single rainbow is produced whose intensity varies periodically as the coating thickness varies. We find good agreement with previous theoretical predictions.     

镀Au键合Ag线性能对键合质量的影响研究

利用扫描电镜、能谱仪、拉力-剪切力测试仪等研究了不同镀Au厚度的镀Au键合Ag线Free Air Ball(FAB)特性和不同力学性能的镀Au键合Ag线对键合强度及其可靠性的影响规律，研究结果表明：镀Au键合Ag线镀层厚度过小会造成Electronic-Flame-Off(EFO)过程中的FAB偏球及球焊点形状不稳定，镀层厚度过大会导致FAB变尖；高强度、低伸长率会造成焊点颈部产生裂纹而造成焊点的拉力偏低并在颈部断裂，低强度、高伸长率引起颈部晶粒粗大进而降低颈部连接强度；镀Au键合Ag线颈部应力集中或内部组织结构不均匀，在冷热冲击周期性形变作用下，球焊点颈部产生裂纹并引起电阻增加，进而导致器件失效.     

A review of wire arc additive manufacturing and advances in wire arc additive manufacturing of aluminium

Although wire arc additive manufacturing (WAAM) has proven its capability of fulfilling demands of production of medium-to-large-scale components for automotive and allied sectors made up of aluminium, at present, WAAM cannot be applied as a fully fledged manufacturing process because of practical challenges such as under-matched mechanical properties, the presence of large residual stresses and mandatory post-deposition operation for the formed component. This paper is a review of WAAM technology including a brief of WAAM history, status, advantages and constraints of the WAAM field. A focus is provided including the efforts directed towards the reduction of porosity, tensile properties, microstructural investigations and other valuable advancements in the field of WAAM of aluminium.

This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

Tribological properties and structural features of pseudoalloys of the aluminum–tin system

We have studied the influence of alloying of aluminum with tin (2–15 mass %) on its wear resistance in a pair with a copper antibody under conditions of friction without lubrication. We have established that, with increase in the tin content in alloys, their wear is reduced to one-sixth to one-fourth. Alloying with tin over 10% leads to the appearance of liquations.     

Failure analysis of thin spray-on liner coated rock cores

Thin spray-on liners (TSLs) are surface support materials used in mining and civil engineering projects since 1990s with a wide ranging area of application from bolt/mesh support replacement to pillar reinforcement systems. This study presents the investigation of pillar reinforcement capacity of the TSL coated andesite rock core by compression test to mimic pillar reinforcement effect. The uniaxial compressive strength (UCS), modulus of elasticity (E), and energy absorbance capacity of uncoated and 5 mm coated cores having 25, 55, 75, and 100 mm diameters were compared. It was observed that there was no significant improvement in strength or stiffness for the homogenous rock cores coated with < 20% (TSL thickness to core diameter ratio) coverage. The main reinforcement contribution of the TSL was observed on post-failure region of the compression tests. Coated samples had higher energy absorbance (toughness) values than uncoated ones while the coverage of the TSL was increased, toughness enhancement also increased. Therefore, pillar reinforcement capacity of a TSL is a function of both pillar diameter and the TSL thickness. A new equation was found between energy absorbance gain for a given core dimeter and the coated TSL thickness. Researches or design engineers can use this equation as a guide to quantify the energy absorbance gain for a given pillar dimension and TSL thickness. It was found that the common on-site TSL practice of application of a fixed thickness (3–5 mm) for a given diameter does not contribute the toughness enhancement or pillar reinforcement.     

电弧增材制造AZ31镁合金组织与力学性能分析

针对镁合金在轻量化结构件领域的应用前景,采用基于MIG焊的电弧增材制造工艺开展了两组不同路径的AZ31镁合金增材实验,并对其微观组织和力学性能进行了分析。结果表明：增材构件相较于原始焊丝的化学成分无较大变化;单道次多层往复堆积路径相较于多道次多层堆积路径,更易制得表面更为平整,内部更为致密的构件,其屈服强度为77.3 MPa,抗拉强度为235 MPa,达到原始焊丝75%的力学性能水平,平均显微硬度为52.7HV,断后伸长率最高达到了27%;增材构件拉伸断裂方式为韧性断裂,并在多道次多层往复堆积构件断口处发现其内部存在气孔。验证了电弧增材制造AZ31镁合金工艺的可行性。     

Tensile properties of carbon nanotube reinforced aluminum nanocomposite fabricated by plasma spray forming

Uniaxial tensile tests were performed on plasma spray formed (PSF) Al–Si alloy reinforced with multiwalled carbon nanotubes (MWCNTs). The addition of CNTs leads to 78% increase in the elastic modulus of the composite. There was a marginal increase in the tensile strength of CNT reinforced composite with degradation in strain to failure by 46%. The computed critical pullout length of CNTs ranges from 2.1 to 19.7 μm which is higher than the experimental length of CNT, leading to relatively poor load transfer and low tensile strength of PSF nanocomposites. Fracture surface validates that tensile fracture is governed strongly by the constitutive hierarchical microstructure of the plasma sprayed Al–CNT nanocomposite. The fracture path in Al–CNT nanocomposite occurs in Al–Si matrix adjacent to SiC layer on CNT surface.     

Tribological properties of silicon nitride ceramics coated with DLC and DLC-Si against 316L stainless steel

Diamond-like carbon (DLC) is an adequate coating on a large variety of materials for tribological purposes, namely against iron alloys in automotive parts, bearings and forming tools. Herein, the tribological properties of DLC-stainless steel couples were assessed by unlubricated pin-on-disc experiments. Plasma enhanced chemical vapour deposition (PECVD) of DLC-Si or pure DLC coatings were performed, respectively, by conventional rf glow discharge from gaseous mixtures of methane and silane or taking only pure methane, with self-bias voltages varying from −200 to −800 V. Silicon nitride (Si₃N₄) was used as DLC substrate aiming the minimisation of adhesion problems, usually found when some metallic substrates are employed. An improved tribological response was obtained with pure DLC coated Si₃N₄ discs sliding against the stainless steel pins. This system almost instantaneously attains a steady-state friction regime with friction coefficients in the range 0.20–0.30 and a wear coefficient value of about 10⁻⁶ mm³ N⁻¹ m⁻¹, one order of magnitude lower than that of the DLC-Si coated ones. The application of a distinct self-bias during the PECVD process only marginally affected the tribological properties of the pure DLC coatings.     

Tribological properties of surfaces

The real area of contact between two solid surfaces is only a small portion of the apparent area. Deformation of these areas can result in solid state contact through surface films. For clean solid-to-solid contact strong adhesive bonding occurs across the interface. Under these conditions many properties of the solid such as the metallurgical and chemical nature of metals can influence adhesion, friction and wear behavior. The presence of gases, liquids and solid films on the surface of solids markedly alters the tribological characteristics. These surface films can also considerably change the mechanical effects of solid state contact on bulk material behavior.     

Microstructure and mechanical properties of spray formed 7055 aluminum alloy by underwater friction stir welding

Ultra-high strength spray formed 7055 aluminum alloy in which Zn is supersaturated solid solution requires strict control of heat input in welding process. In this paper, underwater friction stir welding is carried out in order to reduce heat input comparing with traditional friction stir welding and further improve the joint performances by varying welding temperature history. Through comparing the thermal cycle curves and distribution of residual stress of the plate welded in different media, the reason why the joint welded underwater shows a better performance is figured out. The result shows that tensile strength, hardness and plasticity of underwater welded joint are better than that welded in air. The underwater joint has a fine grained microstructure without “S line” defect, a typically distinct boundary between the weld nugget zone and the thermal mechanically affected zone and a narrow heat affected zone. The main strengthening phase in underwater joint is MgZn₂ .     

Optical properties of plastic scintillators coated with copper, aluminum and silver by magnetron sputtering

Copper, aluminum, and silver thin films are fabricated on plastic scintillators by magnetron sputtering to improve the optical properties. The film morphology is measured by contact mode atomic force microscopy. The optical properties are determined by UV/visible spectrophotometry as well as a single-particle microbeam with proton energy of 2 MeV. Our theoretical analysis suggests a 10.28% increase in the collection efficiency compared to the uncoated plastic scintillator. The improvement in the optical properties is investigated experimentally and the Monte Carlo program SRIM 2008 is employed to investigate the influence of the metal film thickness on the ion stopping and scattering in the materials. Our study suggests that deposition of thin reflecting Cu, Al, and Ag films improves the energy and space resolution of scintillator-based particle spectrometers.     

超音速电弧喷射Ag—Cu共晶熔滴的快速凝固

采用超音速电弧喷射雾化制备Ag-40％（原子分数）Cu共晶合金粉末，用X射线衍射、扫描电镜等对其凝固行为进行研究。结果表明：粉末为球形颗粒，粒径分布90％集中在15～60μm之间、平均粒径为35gm；冷却速率在10^5～10^7K／s范围，最大过冷度不小于232K；粉末富Ag相的平均点阵参数为0．401877nm，Cu的平均扩展固溶度为20．15％（原子分数），直径≤50μm时，点阵参数为0．39252nm，Cu的固溶度达到40％（原子分数），凝固组织为单相亚稳固溶体；对快速凝固行为进行了分析讨论。