Untersuchungen über das Strangpressen kubisch-flächenzentrierter Metalle

Investigation of the extrudability of face-centered cubic metals Part I represents investigations of the behaviour of the interface during the extrusion of lead and lead alloys. The alloying tendency (welding) and the coefficient of friction μ do not show any relationship to the power requirements during the process of extrusion. Due to the high pressure inside the extrusion presses an interfacial movement (friction) can take place only if the coefficient of friction is in the range of μ ≦ 0,001. By knowing the normal pressure and the shear strength of the material the coefficient of friction for slip-stick conditions can be determined from a chart. The dynamic friction is presented as the shearing off of the interfacial contact points and the stationary friction as the creep of these contact points. Attempts to calculate the power requirements of industrial presses on the basis of the shear strength of the material and shear area were successful.     

In-process rheometry as a PAT tool for hot melt extrusion

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.     

Investigation of mechanical properties of 7075 Al alloy formed by forward thixoextrusion process

The thixoextrusion process is a new method for manufacturing complicated and net shape components through which high strength materials can be formed more easily. In this study 7075 Al alloy which has low extrudability has been thixoformed by forward extrusion process. As it is known conventional extrusion of 7075 Al alloy has been very difficult due to high strength and multi-phase microstructural characterization. In this research, by applying the advantages of semisolid processing, the applied pressure for extrusion is decreased and desired mechanical properties were reached near the standard predictable properties for wrought 7075 Al alloy under T6 tempering conditions, for example tensile and yield strength and hardness of samples of thixoextrusion product sufficiently agree with same expected properties of wrought 7075 Al alloy and only elongation is decreased along this process.     

Defining Shape Complexity of Extrusion Dies—A Reliabilistic View

Complexity of the profile being extruded plays a critical role in die design, die reliability, process aberrations, and product defects. Engineering common sense dictates that a more complex die should require a larger amount of extrusion force or pressure. This has been experimentally substantiated by the authors in a recent study. According to a basic definition, therefore, extrusion shape complexity is the ratio of the pressure required to extrude a complex profile to the pressure required for a solid circular profile of the same area. Most of the complexity definitions reported in published literature are based on this interrelationship between extrusion pressure and profile complexity. From a die reliability viewpoint, a complex profile is more difficult to extrude than a simple one, and it generates more stresses in the die. It should therefore lead to an earlier die failure. Another study by the authors confirms that the working life of hot extrusion dies is definitely affected by profile complexity. Reported complexity definitions provide some sort of index to measure extrudability, and can thus be used for pressure prediction to a certain degree. Unfortunately, none of these definitions addresses the very important issue of die reliability, and they generally yield a counterintuitive trend of increasing die life with increasing complexity. None of these definitions includes all the significant geometrical features of a die profile. This article reports the development of two new definitions of shape complexity (linear and power-law) incorporating all significant geometrical features of an extrusion die profile. Die failure data from a large commercial extrusion facility have been collected and analyzed. Regression-based models have been developed for prediction of die failure on the basis of complexity.     

Drainage phenomenon of pastes during extrusion

The effects of elemental powder characteristics, binder content and its composition, as well as some additives on pressure change and drainage phenomenon of pastes during extrusion have been mainly investigated. The pastes consisted of a powder, zirconia or stainless steel, and a water-based binder, an aqueous solution of water-soluble polymer (hydroxypropyl methylcellulose). The drainage phenomenon has been found in extrusion of the stainless steel pastes with lower binder contents, while the zirconia pastes show a small probability of drainage in the range of the binder contents used in this investigation. It is shown that broadening particle size distribution by mixing powders with different average particle sizes has a significant effect on decreasing extrusion pressure and restraining occurrence of the drainage phenomenon, thus improving the extrudability of pastes. It is effective to increase the binder content in pastes, raise the mixing fraction of HPMC in binder and add plasticizer like glycerol, in order to reduce occurrence of the drainage phenomenon during extrusion of the stainless steel pastes.     

Development of response surface model for tensile shear strength of weld-bonds of aluminium alloy 6061 T651

The development of a response surface model to study the influence of process parameters of weld-bonding on tensile shear strength of the weld-bond of 2 mm thick aluminium alloy 6061 T651 sheets has been reported. Significant and controllable process parameters of the weld-bonding (surface roughness, curing time, welding current, welding time and electrode pressure) and their ranges were identified by conducting pilot experiments. Welding current, welding time and welding pressure were identified as significant and controllable parameters. Influence of the significant process parameters and their interaction on the tensile shear strength of the weld-bonds was studied using response surface methodology (RSM). Using model, the optimal combination of weld bonding process parameters for maximum tensile shear strength of the weld bond was obtained. The validity of the model was evaluated on weld bonds developed using different levels of process parameters and testing their tensile shear strength. The model error was found to be in a range of 3–7%.     

Liquid phase bonding of aluminium and aluminium/Nicalon composite using interlayers of Cu-Ag alloy

Abstract

The liquid phase bonding in air of unreinforced and fibre reinforced aluminium using interlayers of Cu-Ag alloy has been investigated. Bond strengths were measured using a simple shear jig and the associated microstructures characterised by electron microscopy and electron probe microanalysis. A shear strength of 65 MN m^-2 was achieved when bonding unreinforced aluminium at 510°C using a 50 μm thick alloy interlayer, and a pressure of 10 MPa for 30 min; the bonded region covered ~85% of the area of the joint. With reinforced aluminium, a bonding pressure of 20 MPa was required to achieve sufficient contact and a similar area of bond; after application of pressure for 30 min at 510°C, a shear strength of 54 MN m^-2 was developed at the joint. The diffusional behaviour and interphase reactions which occurred during the process are discussed and a mechanism for bonding proposed.     

Low-temperature compaction of Ti–6Al–4V powder using equal channel angular extrusion with back pressure

Equal channel angular extrusion (ECAE), with simultaneous application of back pressure, has been applied to the consolidation of 10 mm diameter billets of pre-alloyed, hydride–dehydride Ti–6Al–4V powder at temperatures ≤400 °C. The upper limit to processing temperature was chosen to minimise the potential for contamination with gaseous constituents potentially harmful to properties of consolidated product. It has been demonstrated that the application of ECAE with imposed hydrostatic pressure permits consolidation to in excess of 96% relative density at temperatures in the range 100–400 °C, and in excess of 98% at 400 °C with applied back pressure ≥175 MPa. ECAE compaction at 20 °C (back pressure = 262 MPa) produced billet with 95.6% relative density, but minimal green strength. At an extrusion temperature of 400 °C, the relative density increased to 98.3%, for similar processing conditions, and the green strength increased to a maximum 750 MPa. The relative density of compacts produced at 400 °C increased from 96.8 to 98.6% with increase in applied back pressure from 20 to 480 MPa, while Vickers hardness increased from 360 to 412 HV. The key to the effective low-temperature compaction achieved is the severe shear deformation experienced during ECAE, combined with the superimposed hydrostatic pressure.     

一种细化AZ31镁合金的固液两相区复合挤压工艺

为了通过细化晶粒提高镁合金综合力学性能,基于“工艺耦合,缩短流程”的想法,提出固液两相区挤压剪切复合成形工艺。以AZ31镁合金为研究对象,结合Anycasting技术,对固液两相区成形过程的浇铸过程及凝固过程进行模拟研究;结合实际实验选取合适的挤压参数,从而有效细化AZ31的组织并提高综合性能。结果表明:AZ31在变形区中因枝晶破碎和压力对过冷度的影响等促进了形核,在有效细化晶粒的基础上保证了尺寸的均匀性;且液相的存在有助于协调挤压过程中的变形,减少滑移和孪生变形对织构的影响,显著降低挤压织构的强度,180°角的基面宏观织构极值强度仅为5.3。剪切角能进一步细化晶粒,并提高综合力学性能;当剪切角度为150°时,综合力学性能最优,屈服强度为222 MPa,抗拉强度为309 MPa,伸长率为8%。     

Extrusion processing of Al–Li–Mg–Zr alloy

Abstract

The hot deformation behaviour of an Al–Li–Mg–Zr alloy was characterised in hot torsion and extrusion. The alloy was found to have similar hot ductility to existing high strength aluminium alloys, but this could be maintained at higher temperatures. Billets were extruded over a range of process conditions and a limit diagram was constructed for surface cracking. All the extrusions were found to be partially recrystallised after deformation, but the volume fraction of recrystallisation was a strong function of billet temperature and extrusion ratio. In addition, the unrecrystallised areas contained a recovered substructure where the subgrain size was inversely proportional to the temperature compensated strain rate. The as extruded structure was retained during solution treatment and as a result final mechanical properties were strongly dependent on the extrusion conditions. The use of high billet temperatures and low extrusion ratios gave the best combination of strength and toughness.

MST/839     

Numerische und experimentelle Untersuchungen zur Herstellung von stranggepressten Aluminium/Magnesium‐Werkstoffverbunden und zur Festigkeit des Interface

Numerical and experimental investigations of the production processes of coextruded aluminium/magnesium‐compounds and the strength of the interface In the research project SFB 692 the aim of the subproject B3 is to analyze aluminium/magnesium‐compounds, especially the strength and fracture mechanical properties. Furthermore a numerical model of the interface should be created. In the following paper the main results of the investigations of the subproject are presented. Different influencing variables were analyzed, which determine the quality of the interface. It has been shown, that the compound quality and also the strength of the interface is based on several parameters of hydrostatic and indirect extrusion processes. If the quality of the interface is good, without cracks, the strength is very high. Furthermore the behaviour of the interface under loading in an extended temperature range is presented. A numerical model was found to visualize the behaviour of the compound during the loading tests.     

低压铸造-轧制法快速制备Al-Cu复合材料

采用低压铸造-轧制法实现了快速制备650mm×30mm×7mm×R3.5mm的Al/Cu复合材料,并通过SEM、EDS、XRD和电子万能试验机(AG-X)表征其结构和界面剪切强度。结果表明:在Cu管预热温度200℃,轧制压下率30%,冷却水通量400L/h,Al液温度680~740℃条件下均可实现Al-Cu之间的冶金结合,界面合金层随着Al液温度的升高而变宽;复合材料的导电性能和界面结合剪切强度受界面金属间化合物层宽度的影响,其宽度越宽,剪切强度降低。低压铸造法制备Al-Cu复合材料工艺流程短,一次成形快,并能对界面物相进行有效调控。     

Novel severe plastic deformation technique—accumulated extrusion (AccumEx)

Accumulated extrusion, a novel severe plastic deformation technique based on conventional extrusion process, is proposed and has been validated on commercial pure aluminium sheets. Four sheets were extruded together at 75% reduction, and this product was recut into four pieces and reextruded up to eight passes to a strain of 13.2. The tensile strength increased up to 200?MPa after six passes. The elongation to failure was 21% after one pass and 6% after six passes. Ultrafine grains with average grain size of 600?nm were observed after eight passes. The refinement process was monitored along all three directions. Texture evolution played an influential role on the misorientation profile and high angle grain boundary fraction.     

Mechanical response and structural development during the hot extrusion of a rapidly solidified Al-20Si-7.5Ni-3Cu-1Mg alloy powder

The consolidation of an air-atomized Al-20Si-7.5Ni-3Cu-1 Mg alloy powder was performed utilizing hot extrusion, to determine its extrudability and understand its structural development in relation to process parameters. One of the main features exhibited by the material in this process was a high degree of softening over a peak extrusion pressure, which has been explained by the simultaneous onset of dynamic recovery and recrystallization during deformation. The peak extrusion pressure was shown to be strongly dependent upon the temperature applied, and this dependence has been described with temperature compensated strain rate. It was also observed that the process parameters had a fairly narrow range applicable to the extrusion of the powdered alloy and a significant influence on the deformation behaviour of the powder particles. The combination of heating and deformation, primarily used to convert the loose powder particles into an engineering material, resulted in the decomposition of the meta-stable aluminium matrix and transformations of constituent phases, initially formed in the rapidly solidified powder. Additionally, it was found that the extrusion temperature had an effect on the lattice size and perfection of the as-extruded matrix in the material. Three intermetallic dispersoids containing nickel were detected in the consolidated material, independent of extrusion temperature, and their formation was promoted by hot deformation. The silicon crystal phase in the extruded material was reshaped, and its size was insensitive to the extrusion temperature, which is thought to be caused by a high volume fraction of the coexistent dispersoids. The dispersions of the silicon crystals and intermetallic compounds with various sizes in the matrix substantially modified the deformation mode of the alloy. Evidence of dynamic recrystallization was found, which co-operated with dynamic recovery during deformation, giving rise to a duplex microstructure in the extruded material.     

Extrusion of vapour deposited Al–7·5Cr–1·2Fe (wt-%) alloy (RAE Alloy 72)

Abstract

Techniques and equipment were developed for the extrusion of vapour deposited RAE Alloy 72. The alloy was extruded at temperatures from 300 to 420°C and extrusion ratios from 2:1 to 25:1. Room and elevated temperature strengths and smooth S–N (stress–number of cycles to failure) fatigue properties were determined for a range of extrusions. The best extrusions gave room and elevated temperature strengths that were comparable to those of rapidly solidified aluminium alloys. The fatigue strength/tensile strength ratio of >0·5 was higher than would be expected for an aluminium alloy.

MST/1350     

Extrusion granulation and high shear granulation of different grades of lactose and highly dosed drugs: a comparative study

Formulations containing different lactose grades, paracetamol, and cimetidine were granulated by extrusion granulation and high shear granulation. Granules were evaluated for yield, friability, and compressibility. Tablets were prepared from those granules and evaluated for tensile strength, friability, disintegration time, and dissolution. The different lactose grades had an important effect on the extrusion granulation process. Particle size and morphology affected powder feeding and power consumption, but had only a minor influence on the granule and tablet properties obtained by extrusion granulation. In contrast, the lactose grades had a major influence on the granule properties obtained by high shear granulation. Addition of polyvinylpyrrolidone (PVP) was required to process pure paracetamol and cimetidine by high shear granulation, whereas it was feasible to granulate these drugs without PVP by extrusion granulation. Granules prepared by extrusion granulation exhibited a higher yield and a lower friability than those produced by high shear granulation. Paracetamol and cimetidine tablets compressed from granules prepared by extrusion granulation showed a higher tensile strength, lower friability, and lower disintegration time than those prepared from granules produced by high shear granulation. Paracetamol tablets obtained via extrusion granulation exhibited faster dissolution than those obtained via high shear granulation. For all lactose grades studied, extrusion granulation resulted in superior granule and tablet properties in comparison with those obtained by high shear granulation. These results indicate that extrusion granulation is more efficient than high shear granulation.     

Preliminary evaluation of hot extrusion miniaturization

Experiments were conducted to examine the feasibility of hot extruding metals on a miniature scale thus providing a quick and cheap method of studying extrusion in general. Aluminium was successfully extruded using a new miniature hot extrusion rig, producing aluminium wires (maximum diameter 2.6 mm) as opposed to rods. A preliminary comparison of extrusion pressures on the miniature rig and on a larger extrusion press was conducted. The effects of temperature, extrusion speed and extrusion ratio on the extrusion pressure were examined for both miniature and larger scale extrusions. Extrusion speed had little effect on extrusion pressure, because the range of speeds examined was too small (due to speed limitations on the larger extrusion press). Both extrusion sizes generally displayed similar dependencies on temperature and extrusion ratio. However, the extrusion pressures for miniature extrusions were found to be always lower than for the larger scale extrusions. This may have been due the evaluation of parameters in the expression used for strain rate in the comparison. Finite element analysis may prove useful in gaining a fuller understanding of the miniaturization process.     

Effect of particle packing on extrusion behavior of pastes

Two powders with different average particle sizes and size distributions were blended in various proportions. The influence of powder mixing on extrusion behavior of pastes containing a water-based binder has been examined. The bimodal mixed stainless steel powder exhibits a low extrusion pressure, small amount of binder and high green density when the mixing fractions of large and small particles are approximately equal. With regard to the mixing of zirconia and stainless steel powders, a similar result has been found, but the mixing fraction of powder corresponding to the optimal packing is shifted to stainless steel-side. In order to improve the extrudability of pastes, it is effective to mix two powders with a large difference in particle size.     

带有橡胶垫层的混凝土接触特性试验及其内聚力模型

针对带有橡胶垫层的混凝土试件,通过直剪试验研究了带有橡胶垫层的混凝土接触摩擦特性。采用PPR内聚力模型表征接触面的接触摩擦特性,对试验结果进行了模拟分析。试验结果表明：在带有橡胶垫层的混凝土接触面剪切过程中,剪切应力与剪切位移的变化过程可分为弹性、弹塑性硬化和应变软化变形阶段。当轴向应力在1.5 MPa~13 MPa范围内时,残余强度与剪切强度比在55%~65%,当轴向应力为17 MPa和21 MPa时,残余强度与剪切强度比大约分别为70%、80%。橡胶垫层在混凝土之间起到良好的缓冲作用。在轴向应力较大时,接触面的应力变形会伴有明显的软化变形阶段。利用Archard非线性幂次准则描绘了剪切峰值应力与轴向应力的关系,准则中常数k和m分别为0.97和0.33。PPR内聚力模型计算表明剪切应力随剪切位移变化关系曲线与试验结果基本吻合,为研究盾构管片块体间的接触摩擦作用研究提供借鉴。     

Oxidation of iron, aluminium and titanium films in the temperature range 50–200 °C

The oxidation kinetics of iron, aluminium and titanium films have been studied in the temperature range 50–200 °C at a pressure of 0.7 Pa with a piezoelectric quartz microbalance. For titanium, additional measurements in the pressure range 7 × 10⁻³ – 70 Pa have been carried out. All three metals under investigation showed qualitatively common features in their oxidation behaviour: a very fast initial oxygen absorption step, completed in less than 1 min, followed by a slow, temperature-independent oxide growth with logarithmic time law at lower temperatures, and an enhancement of the oxidation rate at higher temperatures. The oxidation curves are compared with the results of model calculations based on the Cabrera-Mott theory.