Effects of TiB2 particle addition on the expansion,structure and mechanical properties of PM Al foams

Addition of TiB₂ particles to Al–TiH₂ powder compacts results in a significant increase in foam expansion, due to a reduction in the minimum cell wall thickness, but does not affect stabilisation of the foam. Composite foams were found to have higher proof stresses and absorb more energy than Al foams.     

A study of aluminium foam formation—kinetics and microstructure

Aluminium foams were produced by applying the powder compact melting method, i.e. by mixing metal powders and powdered gas-releasing blowing agents and pressing them to a foamable precursor material after this. The resulting precursor was then foamed by heating it up to above its melting point inside an “expandometer”, which allowed for the volume and temperature to be measured throughout the entire process. The present studies comprise the effects of the aluminium alloy composition (AlSi7 and 6061), some of the pressing parameters of the foamable precursor material, the foaming temperature and the heating rate during foaming on the expansion behaviour of the foam. Moreover, the morphological and microstructural evolution of metal foams is investigated.     

A new lubricant carrier for metal forming

A lubricant carrier for metal forming processes is developed. Surfaces with pores of micrometer size for entrapping lubricant are generated by electrochemical deposition of an alloy, consisting of two immiscible metals, of which one metal subsequently is etched away leaving 5 μm layers with a sponge-like structure. The pores will act as lubricant reservoirs during severe forming processes. The deposited microporous layer is evaluated by friction tests in the form of ring compression tests and double cup extrusion tests. Furthermore the anti-seizure properties are investigated by single cup extrusion at high reduction and excessive stroke comparing with conventionally lubrication using phosphate coating and soap.     

A new forming method of solid bosses on a cup made by deep drawing

A new process for forming bosses on the bottom of a cup made by deep drawing is proposed: solid bosses are formed by compression of the cup bottom during deep drawing. By the combined effect of compression and deep drawing, bosses are formed with a lower load than simple compression or backward extrusion. It is found that high bosses can be formed with moderate punch pressure when only one side of the blank is lubricated.     

Comparison Through Image Analysis Between Al Foams Produced Using Two Different Methods

Several methods are available for making metal foams. They allow to tailor their mechanical, thermal, acoustic, and electrical properties for specific applications by varying the relative density as well as the cell size and morphology. Foams have a very heterogeneous structure so that their properties may show a large scatter. In this paper, an aluminum foam produced by means of foaming of powder compacts and another one prepared via the infiltration process were analyzed and compared. Image analysis has been used as a useful tool to determine size, morphology, and distribution of cells in both foams and to correlate cell morphology with the considered manufacturing process. The results highlighted that cell size and morphology are strictly dependent upon the manufacturing method. This paper shows how some standard 2D morphological indicators may be usefully adopted to characterize foams whose structure derives from the specific manufacturing process.     

Manufacturing of Al–Mg–Si alloy foam using calcium carbonate as foaming agent

Aluminium foams can be manufactured by two main methods: casting and powder metallurgy. When the latter route is used, a foaming agent (usually TiH₂) is mixed with the aluminium or aluminium alloy powders, followed by powder mixture consolidation (usually hot extrusion) into a precursor and finally its foaming treatment. In this research, two calcium carbonate powders were used as foaming agents on an Al–Mg–Si (AA6061) alloy. Their different characteristics (particle size and chemical composition) modified the manufacturing process to achieve the final foam. AA6061 powders were then mixed with 10% calcium carbonate and, after cold isostatic pressing into green cylinders, hot extruded at different temperatures (475–545 °C). The foaming treatment was carried out in a furnace preheated to 750 °C using several heating times. The density changed from 2.03 to 2.10 g/cm³ after cold isostatic pressing to 2.64–2.69 g/cm³ in precursor materials obtained by hot extrusion. Foaming behaviour depends on the carbonate powder as well as the extrusion temperature. Thus, natural carbonate powder (white marble) produces a foam density close to 0.65 g/cm³ after a shorter time than when chemical carbonate is used. The foam structure showed a low degree of aluminium draining, no wall cell cracks and a good fine cell size distribution. Compressive strength of 6.11 MPa and 1.8 kJ/m³ of energy absorption were obtained on AA6061 foams with a density between 0.53 and 0.56 g/cm³.     

Mechanism of dissolution of flux containing Mn–Al compacts in molten aluminium

Abstract

Dissolution and recovery of Mn–Al compacts with and without a chloride flux was studied by analysing the Mn content of the specimens taken from the melt after the addition of the compact. In the second set of experiments the compacts were heated in a resistance furnace while a thermocouple was in close contact with them and the temperature was recorded. Thermal gravimetric analysis was also carried out to study the oxidation rates of the powder mixtures. The results showed that the intermetallic forming reactions, in the fluxed compacts starts at significantly lower temperatures in comparison with non-fluxed compact. It is concluded that at first the flux removes the oxide layer out of the surfaces of powder particles and leaves behind active surfaces. Afterwards, the exothermic reactions of forming Mn–Al intermetallics start at solid/solid interfaces at low temperatures, below the melting point of Al.     

气体发生器关键零件热挤压工艺及数值模拟研究

通过对气体发生器零件的分析,提出了金属最后充满模膛位置的判断参数,并用DefORm-2D对其冷挤压和热挤压过程进行了有限元模拟分析,比较了两种挤压过程中的物理量场。通过计算机模拟看出,热挤压是更为经济合理的方案。采用工艺试验验证了模拟结果。     

Fabrication of aluminium foams from powder by hot extrusion and foaming

In order to produce aluminium foams for light-weight and energy absorbing structures of automobiles, a method for fabricating aluminium foam from powder mixed with a foaming agent by using a mould is proposed. The method consists of four sequential processes: powder compacting, extruding, foaming and moulding. In the experiment for fabricating aluminium foam from powder, the conditions of powder extrusion and foaming by the heated die are determined from the density of the aluminium foams made without a mould. The experimental results show that the relative density of the aluminium foam made under appropriate conditions is 0.22. In moulding of aluminium foam, a stainless steel pipe is used as a mould and the cylindrical aluminium foam is produced by filling into the pipe mould. The distribution of relative density within the aluminium foam bar is in a range of 0.2–0.3 by rapid cooling of the pipe. To examine the ratio of deformation energy to weight of the pipe including the aluminium foam, a compression test using a press is carried out. The deformation energy of the pipe can be increased with aluminium foam filled by the proposed method.     

金属塑性加工的物理模拟

物理模拟是进行体积成形工艺研究和生产设计的重要工具方法 ,这种方法简捷、直观 ,还可以预测材料流动情况、填充情况和工艺缺陷形成过程。本文介绍了利用北欧新型模拟材料“菲蜡” ( Filia)进行体积成形物理模拟实验的方法、原理、设备装置、模具和模拟材料的特性。对圆柱坯料的自由镦粗、正挤、反挤、管件变薄挤压、平板坯料平面应变镦粗进行了物理模拟 ,分析讨论了物理模拟实验结果 ,并与上限模拟软件的结果进行了对比。     

采用TiH2粉末和造孔剂NH4HCO3烧结多孔钛（英文）

采用 TiH2和造孔剂 NH4HCO3混合粉末,利用粉末烧结法制备了多孔钛。研究表明,NH4HCO3的添加对于烧结的多孔钛的相组成几乎没有影响。多孔钛的孔隙度、平均孔隙尺寸、压缩强度和压缩弹性模量随 NH4HCO3添加量的增加而急剧下降。多孔钛可用添加不同量的造孔剂来调整孔隙结构和力学性能。独特的孔隙结构和适宜的力学性能满足多孔植入材料的基本要求。表明烧结的多孔钛是有前景的多孔植入候选材料。     

Using microwaves to synthesize pure aluminum and metastable Al/Cu nanocomposites with superior properties

The processing of aluminum using powder metallurgy techniques is a challenging task due to the presence of thin oxide films on the surface of the metal particles which prevent strong bonding between particles during sintering. In this study, an innovative hybrid microwave sintering technique is utilized to process pure aluminum and Al/Cu nanocomposites without the need of any protective atmosphere. Hybrid microwave sintering involves the heating of aluminum compacts using both microwave energy and radiant heating. Significant savings in time and energy can be achieved using the fabrication methodology. Results revealed that processing methodology used in this study provides a simple and inexpensive option to existing processing methodologies to synthesize pure Al and Al/Cu nanocomposites with superior combination of properties.     

Early stage consolidation mechanisms during hot isostatic pressing of Ti–6Al–4V powder compacts

Mechanisms contributing to early stage compaction of metal powder compacts were identified in a series of Ti–6Al–4V powder compacts hot isostatically pressed to relative densities ranging from 71% to 100%. The partially dense compacts, consolidated from loose powder in thin-walled containers, were examined using optical microscopy of polished sections and stereo pair scanning electron microscopy of fracture surfaces. Relative particle motion, characterized by small relative movements of particles and clusters of particles, was found to contribute significantly to compaction over a broad range of relative densities (from 63% to 90%). A mechanism was identified by which the preferential deformation of small particles at large–small particle contacts enables rigid body motion of larger particles which, in turn, increases the relative density of the compact. Tensile fractures within the compact occurred between 82% and 90% relative density providing direct evidence of cooperative movement among clusters of particles. In comparisons with mechanistic powder compaction models, measurements of particle deformation, contact areas, and coordination numbers were found to substantiate the importance of the experimentally identified mechanisms.     

Influence of the casting and mould temperatures on the (micro)structure and compression behaviour of investment-cast open-pore aluminium foams

Current literature offers only limited information about the influence of the casting and mould temperatures on the properties of cast aluminium foams. In order to close this current research gap, the casting and mould temperatures were varied during the production of investment-cast open-pore A356 foams. The results show that a decreased mould temperature and an increased casting temperature lead to increased mechanical properties during the static compression testing of open-pore 10 and 15 ppi (pores per inch) A356 foams. This increase is due to a reduced number of eutectic silicon particles and increased strut diameter resulting from the better mould-filling ability of the melt. The effect of the process parameters is statistically significant for the mechanical properties of the 15 ppi foams. This is probably due to this foam type’s lower strut diameter; compared to the bigger 10 ppi foam struts, since these thinner struts are more sensitive to the high number of the silicon phase and to the decreased strut diameter due to a reduced mould-filling ability. In addition to this, a change of the cooling rate has a larger impact on small strut diameters. With the aid of the present results, the influence of the process parameters on the mechanical properties of open-pore 15 ppi foams was modelled and confirmed by reference test runs.     

40Cu-W合金伪半固态触变模锻成形研究

采用基于粉末成形及半固态成形工艺而提出的伪半固态触变模锻成形工艺,成功制备出力学性能良好的40Cu-W合金筒形件,其中在成形温度为1 350 ℃、模锻压力为500 MPa工艺条件下制件的抗弯强度可达1 151 MPa,致密度达到98.38%.制件微观组织致密,分布比较均匀,低熔点的铜相包围在钨颗粒的周围,为制件性能的提高起到了重要作用.     

The oxidation behavior of gas-atomized Al and Al alloy powder green compacts during heating before hot extrusion and the suggested heating process

The oxidation behavior of gas-atomized Al and Al alloy powder green compacts during heating prior to hot extrusion compaction was studied at laboratory and industrial scales by TGA, DSC, DTA, EDX, TEM and XRD methods. The effect of the heating of green compacts on the mechanical properties of the powder-extruded samples was assessed. Significant oxidation of Al and Al alloy powder green compacts takes place in the solid state during heating in air. The onset and intensity of oxidation were affected by the Mg content, the surface area of the powder and the volume of the powder green compacts. An exothermic heat associated with the oxidation of Al and Al alloy powders resulted in intense overheating of bulky powder green compacts during heating in air. The samples extruded from the powder green compacts heated in air exhibited reduced strength. The loss in strength was especially pronounced in the case of Mg-containing Al alloy powders. Mg diffuses from a powder metallic core toward the native Al₂O₃ surface layer present on as-atomized Al alloy powders; it reacts with oxygen present in air and in the Al₂O₃ surface layer where the MgO phase forms, eventually resulting in the depletion of Mg from the powder core. Materials extruded from Al powders depleted of Mg do not exhibit effective Al-Mg solid solution strengthening or strengthening by Mg-containing precipitates. Economically viable approaches to avoiding the detrimental effects of powder oxidation during the heating of green compacts prior to hot working consolidation are discussed.     

钟形壳温-冷联合挤压工艺优化分析

根据挤压成形理论,分析、制订了钟形壳温-冷联合挤压成形工艺。采用数值模拟和工程实践相结合的方法,对钟形壳成形过程进行数值模拟和工艺优化。针对初始工艺试制中出现充填不满的缺陷,通过分区转移和材料分流的方法进行工艺方案的改进。制定的优化工艺方案为温反挤(锥冲头)—整形(凹模车沉孔D60)。对方案结果进行验证说明,采用该方案得出的金属流线合理,微观组织符合要求。     

添加造孔剂法制备开孔泡沫铝及其性能研究

以球形尿素颗粒为造孔剂,采用传统的粉末冶金工艺制备开孔泡沫铝并研究了其性能.结果表明,添加造孔剂法制备的泡沫铝可以任意控制孔隙率及孔径的大小,且孔结构良好,保持了造孔剂的形状;高的烧结温度使泡沫铝的压缩强度提高,但过高的温度将导致孔壁熔化.本试验制成的泡沫铝其压缩曲线和泡沫金属典型压缩曲线相似,且抗压强度和经典理论计算结果一致.     

闭孔泡沫铝的电磁屏蔽性能

采用粉末冶金发泡法制备闭孔泡沫铝,通过调整发泡剂含量、发泡温度、粘度、保温时间等手段,制得孔隙率可调、孔洞分布均匀的闭孔泡沫铝样品,并测试了不同孔隙率、孔径泡沫铝样品的电磁屏蔽性能.结果表明:在100～1000MHz内,泡沫铝的电磁屏蔽性能在60～90dB之间,且随着孔隙率、孔径的增加,泡沫铝的电磁屏蔽性能下降.     

Hole flanging with cold extrusion on sheet metals by FE simulation

Flange height and lip thickness are generally restricted by the formability of sheet metals in the conventional hole flanging operation. In the current work, cold extrusion was applied and a special forming die set was designed with a stripper subjected to counter-pressure with an aim to obtain a more substantial flange. FEM software DEFORM was utilized to simulate this flange extrusion process with two forming conditions: forming with a fixed die cavity and forming with the stripper subjected to counter-pressure. The results showed the cup preform tended to buckle on its bottom with insufficient counter-pressure. The cup preform would start extruding a flange when critical counter-pressure was reached. The magnitude of the critical counter-pressure increased in flange extrusion of smaller inner diameters. The corresponding overall forming load was greatly reduced as compared to flange extrusion with a fixed die cavity.