Production of Metallic Foams From Ceramic Foam Precursors

A process has been developed for obtaining closed cell metallic foams using a ceramic foam precursor. In this approach, the major constituent of the ceramic foam precursor is iron oxide (Fe₂O₃), which is mixed with various foaming/setting additives. The mixture sets rapidly at room temperature to stabilize the foam generated by hydrogen release. The oxide foam is then reduced in a non‐flammable hydrogen/inert gas mixture to obtain a metallic foam with a cell diameter of 0.5–2 mm. Iron foams with a relative density of 0.23 were tested in compression and yielded an average compressive strength of ～ 34 MPa. The compressive stress‐strain curves obtained were typical of cellular metals. The normalized strengths of the metal foams obtained in the present study compare very favorably with that of steel foams produced by other techniques.     

Cellular Metals Manufacturing

Open cell, stochastic nickel foams are widely used for the electrodes and current collectors of metal – metal hydride batteries. Closed cell, periodic aluminum honeycomb is extensively used for the cores of light, stiff sandwich panel structures. Interest is now growing in other cell topologies and potential applications are expanding. For example cellular metals are being evaluated for impact energy absorption, for noise and vibration damping and for novel approaches to thermal management. Numerous methods for manufacturing cellular metals are being developed. As a basic understanding of the relationships between cell topology and the performance of cellular metals in each application area begins to emerge, interest is growing in processes that enable an optimized topology to be reproducibly created. For some applications, such as acoustic attenuation, stochastic metal foams are likely to be preferred over their periodically structured counterparts. Nonetheless, the average cell s ize, the cell size standard deviation, the relative density and the microstructure of the ligaments are all important to control. The invention of more stable processes and improved methods for on‐line control of the cellular structure via in‐situ sensing and more sophisticated control algorithms are likely to lead to significant improvements in foam topology. For load supporting applications, sandwich panels containing honeycomb cores are much superior to those utilizing stochastic foams, but they are more costly than stochastic foam core materials. Recently, processes have begun to emerge for making open cell periodic cell materials with triangular or pyramidal truss topologies. These have been shown to match the stiffness and strength of honeycomb in sandwich panels. New cellular metals manufacturing processes that use metal textiles and deformed sheet metal are being explored as potentially low cost manufacturing processes for these applications. These topologically optimized systems are opening up new multifunctional applications for cellular metals.     

板料激光成形的正交实验设计与量纲分析

激光弯曲是一种利用激光加热来实现构件的柔性成形技术。利用正交实验研究各可控因素对弯曲角度的影响,通过量纲分析建立数学模型,根据正交实验数据对数学模型的相应参数进行回归求解。研究结果表明,利用正交实验可对激光成形的工艺参数进行全面评估;利用量纲分析法仿真复杂的激光弯曲过程是简便有效的。     

Creep Response of Sandwich Beams with a Metallic Foam Core

The creep response of metallic foam sandwich beams in 3‐point bend is investigated numerically for the case of a metallic foam core and two steel faces. The face sheets are treated as elastic, while the foam core is modeled by a viscoplastic extension of the Deshpande‐Fleck yield surface. This power‐law creeping constitutive law has been implemented within the commercial finite element code ABAQUS. It is found that the beams creep by a variety of competing mechanisms, depending upon the choice of material properties and the geometric parameters. A failure map is constructed and effect of rate dependence on the load‐deflection curves is quantified, and compared against the available experimental data.     

不锈钢/铝合金异种金属激光-MIG熔钎焊工艺研究

分别采用激光-MIG复合焊和单MIG焊,实现了2mm厚的304不锈钢和6061铝合金对接接头的熔钎焊,对比了不同焊接热源对接头显微组织、界面层化合物及力学性能的影响。结果表明,采用激光-MIG复合焊可以获得性能良好的不锈钢-铝对接接头。激光-MIG复合焊接头的界面层化合物为FeAl_2和Fe_4Al_(13),厚度约为5μm;而单MIG焊接头的界面层化合物厚度约为3μm,主要为Fe_4Al_(13)。激光-MIG复合焊接头的抗拉强度为105MPa,比单MIG焊接头提高了10.8MPa,达到铝合金母材的33.9%。接头试样拉伸断裂均起裂于钎焊界面处,并向余高处扩展,且由脆性断裂转变为韧性断裂。     

Processing of Titanium Foams

Because of their excellent mechanical properties, low density and biocompatibility, titanium foams are attractive for structural and biomedical applications. This paper reviews current techniques for titanium foam processing, which are all based on powder‐metallurgy because of the extreme reactivity of liquid titanium. A first group of processes is based on powder sintering with or without place‐holder or scaffolds. A second group relies on expansion of pressurized pores created during prior powder densification.     

Dissimilar Joining of Aluminum to Copper Using Ultrasonic Welding

Joint of aluminum to copper sheets with an Al2219 particle interlayer was successfully achieved by ultrasonic spot welding (USW). Effects of clamping pressure and surface activation on the microstructure and mechanical performances of the joints were systematically studied. It turned out that the optimal clamping pressure is 60 psi, and surface activation is beneficial to obtain a sound joint. On combining the actions of optimal clamping pressure and surface activation, the interfacial combination was highly intimate, and more plastic deformation occurred in the weld interface. Appropriate clamping pressure (30–60 psi) was beneficial to the weld interface bonding, whereas beyond the critical value (60 psi) aluminum beneath the sonotrode tip would be squeezed out of the weld interface.     

金属结构焊缝的疲劳设计

本文讨论分析了目前金属结构焊缝的设计方法，介绍了焊缝疲劳设计的方法及公式，提出了提高金属结构焊缝疲劳强度的一些措施。     

Potential New Matrix Alloys for production of PM Aluminium Foams

The powder compact melting technique for aluminium foam production as practised today accepts a certain mismatch between foaming agent decomposition and matrix alloy melting temperatures. This mismatch is believed to influence the pore structure in an unfavourable way. Adjustment of TiH₂ decomposition as well as liquidus and solidus temperatures of matrix alloys can be used to counteract it. Effects of TiH₂ thermal treatments are investigated using thermal analysis. TiH₂ variants gained via annealing treatments were used to produce aluminium foam precursor materials. As matrix for these specimens, aluminium based alloys with low liquidus and solidus temperatures were selected. Alloy systems considered include established combinations of aluminium with Cu, Mg, Si and Zn as well as special quaternary mixtures of these elements. First examinations presented include thermal analysis of alloys as well as studies on expansion vs. time and temperature relationships of precursor material based on new alloys and foaming agent variants.     

我国焊接材料的发展趋势

近年来,我国焊接材料的产量占到世界总产量的一半以上,并且随着国民经济的发展,我国焊接材料的消耗量仍将保持增长趋势。并且钢材品质的提高及品种的完善,对焊接材料提出了更高的技术要求。本文论述了近几年国内焊接材料的应用现状,分析了焊接材料的应用领域,总结出我国焊接材料的发展趋势。     

陶瓷-金属焊接的方法与技术

概述了陶瓷-金属焊接的特点,综述了常见的6种焊接方法,包括钎焊、扩散连接、过渡液相连接、自蔓延高温合成连接、热压反应烧结连接和摩擦焊等,重点介绍了它们的工艺特点和研究现状.在此基础上,比较了各种方法的优缺点和适用范围,并对陶瓷-金属焊接的研究前景进行了展望.     

Fabrication of Lotus‐type Porous Metals and their Physical Properties

Lotus‐type porous metals whose long cylindrical pores are aligned in one direction were fabricated by unidirectional solidification in a pressurized gas atmosphere. The pores are formed as a result of precipitation of supersaturated gas when liquid metal is solidified. The lotus‐type porous metals with homogeneous size and porosity of the evolved pores produced by a mould casting technique are limited to the metals with high thermal conductivity. On the other hand, the pores with inhomogeneous pore size and porosity are evolved for metals and alloys with low thermal conductivity such as stainless steel. In order to obtain uniform pore size and porosity, a new “continuous zone melting technique” was developed to fabricate long rod‐ and plate‐shape porous metals and alloys even with low thermal conductivity. Mechanical properties of tensile and compressive strength of lotus‐type porous metals and alloys are described together with internal friction, elasticity, thermal conductivity and sound absorption characteristics. All the physical properties exhibit significant anisotropy. Lotus‐type porous iron fabricated using a pressurized nitrogen gas instead of hydrogen exhibits superior strength.     

7A52铝合金薄板搅拌摩擦焊焊缝的组织形貌

采用自行研制的便携式搅拌摩擦焊设备,对厚度为3mm的7A52铝合金薄板进行焊接试验。用金相显微镜、扫描电镜等分析测试手段,分析了焊缝的微观组织结构。焊缝可分为焊核、热机影响区、热影响区等三个区域。焊核为细小均匀的等轴晶,晶粒明显细小;热机影响区出现了晶粒粗化现象,由母材的细纤维组织变为具有弧度的弯曲粗纤维组织;热影响区组织发生了回复、再结晶和粗化。     

超声在电弧焊接中的应用

超声场作为一种高效清洁的物理场在电弧焊接中具有越来越多的应用。在电弧焊接过程中,引入超声,可以有效改善电弧形态、熔滴过渡以及焊缝组织,最终提高焊接接头力学性能。超声在电弧焊接过程中的应用特点主要与超声施加方法有关,不同的超声施加方法具有不同的特点,根据不同的超声施加方法可将超声电弧复合焊接分为不同类型。主要综述了电弧超声技术、超声与电弧同轴复合、超声作用于焊丝以及超声工具头作用于固体母材或者焊缝表面4种技术的各自特点及研究进展,着重分析了不同技术的设备特点及其对组织与力学性能的影响。最后对该方向的研究进展进行了总结,并对其发展前景和主要发展方向进行了展望。     

不锈钢薄板焊接裂纹成因分析

某不锈钢薄板在钎焊过程中产生裂纹,通过对裂纹表面的宏观形貌、微区形貌以及微区成分进行分析,查明了其开裂原因。结果表明:由于在钎焊过程中有铜粒子熔化渗入到不锈钢的晶粒边界,在晶粒边界形成脆性液膜,因此铜脆是导致该不锈钢薄板产生裂纹的主要原因。最后根据开裂原因提出了相应的改进措施和建议。     

异种有色金属电磁脉冲焊接研究现状及发展趋势

电磁脉冲焊接技术由电磁脉冲成形技术演化而来,通过电磁力驱动被焊接金属发生高速碰撞,实现碰撞界面的冶金结合进而获得焊接接头,作为一种固相连接技术,尤其适用于性能差异显著的异种材料焊接。随着国内外研究者对电磁脉冲焊接技术的深入研究,发现该技术在铝与镁、铝与铜、铝与钛、铝与镍钛等异种有色金属焊接领域的应用前景日益广阔。然而,目前缺乏对异种有色金属电磁脉冲焊接研究现状及发展趋势的综述研究,未能明确该技术在异种有色金属焊接中存在的问题和发展方向。因此,本文详细探讨了异种有色金属电磁脉冲焊接接头的微观结构特征、元素分布规律及显微组织特性,并阐述了接头形成机理,主要包括碰撞界面结合模型和缺陷形成机制。研究发现,不同异种有色金属组合的焊接界面结构明显不同,电磁脉冲焊接接头的力学性能优化需要通过进一步揭示焊接界面结构的形成机制来实现,电磁脉冲焊接技术难以对电学性能差、厚度大以及强度高的材料进行高质量焊接,需要加强相关辅助焊接技术、辅助装备的研究开发。最后对电磁脉冲焊接技术在异种有色金属的焊接过程中存在的问题及未来发展方向进行了展望,提出了未来该技术的研究发展方向,为电磁脉冲焊接技术的相关研究奠定了基础。     

大块金属玻璃焊接研究进展

综述了大块金属玻璃焊接领域的最新进展;介绍了成功焊接大块金属玻璃的不同方法,包括爆炸焊、电火花焊、电子束焊、用多层金属片进行焊接等熔化焊,以及固相下的摩擦焊.熔化焊接方法的成功,原因在于大块金属玻璃的玻璃态成型能力和在这些方法中高的线能量;而摩擦焊接的成功,则是由于金属玻璃在过冷液相区的热稳定性以及在该区域的超塑性和粘滞性.