转模挤压成形过程的变形机理研究

针对低塑性合金挤压成形时所需能耗大、材料利用率低等问题,提出了对凹模施加转动的成形新工艺———转模挤压成形技术,并设计了特殊的凹模结构.与芯模转挤压仅适于圆截面制品相比,对凹模施加转动可有效地避免异型截面制品挤出成形时引起的垂直模口部位轴向的＂切断＂等难题.数值模拟及理论分析表明：与普通挤压相比,凹模转挤压成形中塑性区...     

铝锂合金复合材料研究现状

铝锂合金复合材料是目前铝锂合金研究的热点。本文重点介绍和评述了这种材料的主要制备方法、时效特性及目前达到的力学性能。     

阳极氧化处理增强Al-Li合金胶接板剪切强度的机理

为揭示磷酸阳极氧化处理后Al-Li合金胶接接头剪切强度大幅度增强的机理,分别对其进行机械打磨和磷酸阳极化表面处理,并选用不同的分析仪器对表面处理后的Al-Li合金表面微观形貌、粗糙度、表面润湿性和表面自由能进行测试计算和分析。结果表明,机械打磨后仅在Al-Li合金表面留下纵横交错的沟槽,而磷酸阳极化处理后使得Al-Li合金表面产生了微观粗糙的多孔膜,增加了胶层与合金表面的接触面积,改善了胶质分布的均匀性;磷酸阳极化处理后Al-Li合金表面自由能明显提高,改善了粘接界面的润湿性能。两方面的共同作用,使得胶接界面的抗剪切能力大幅提高。     

Indigenization of high-strength,light-weight Al-Li alloys for aerospace

A research programme was initiated at the Defence Metallurgical Research Laboratory, Hyderabad, a decade ago for the indigenous development of Al-Li alloys in order to finally meet the requirements of the space and aircrft industries in the country. This paper describes the systematic studies carried out in the laboratory to overcome the initial difficulties in producing sound ingots, optimize the subsequent heat treatments and processing schedules, and to finally obtain reproducible microstructure and mechanical properties in the semi products (i.e. sheets and extrusions) developed. Laboratory-scale sheet and extrusion products meet tensile property specification of 8090 alloy. One of these semiproducts, i.e. round bar extrusion, is currently being supplied for the stallite programmes. Commercial-scale sheet products made in Russia under an Indo-Russian joint programme have been made available for the aircraft programme. Recent alloy development studies in the laboratory are discussed within the context of the present paper.     

挤压铸造与超声处理对铸造铝锂合金组织与性能的影响

目的 研究挤压铸造与超声处理工艺对铸造铝锂合金组织与性能的影响规律,分析工艺改变对组织细化及性能提升的作用机理,解决传统重力铸造下铝锂合金性能较差的问题。方法 将挤压铸造(SC)与超声处理(UT)相结合制备Al-2Li-2Cu-0.5Mg-0.2Zr合金,在熔体超声2 min后,以50 MPa的挤压力制备合金,探究各工艺对铸造铝锂合金显微组织与力学性能的影响。结果 与传统的重力铸造(GC)相比,SC合金的孔隙率和成分偏析显著降低,晶粒尺寸也明显减小,特别是经过UT+SC处理的合金得到了进一步优化。经UT+SC处理后,Al-2Li-2Cu合金的极限抗拉强度(UTS)、屈服强度(YS)和伸长率分别为235 MPa、135 MPa和15%,与GC合金相比,分别提高了113.6%、28.6%、1 150%,与SC合金相比,分别提高了5.4%、3.8%、15.4%。结论 UT+SC工艺能明显提升铸造铝锂合金的性能。UT+SC制备的Al-Li合金的强度和伸长率的提高归因于孔隙率的降低、晶粒细化和第二相的均匀分布。将挤压铸造与超声处理相结合制备铸造铝锂合金解决了重力铸造下合金性能较差的问题,为满足航空航天要求的高强韧铸造铝锂合金的制备提供了一种行之有效的新方法。     

铝锂合金研究开发的历史与现状

综述了国内外关于铝锂合金的研究概况；对铝锂合金的实际应用进行了简要归纳；分析和评述了铝锂合金今后的发展态势。     

Finite Element Simulations of Four-holes Indirect Extrusion Processes of Seamless Tube

Finite element simulations are performed to investigate the plastic deformation behavior of Ti-6Al-4V titanium alloy during its indirect extrusion through a four-hole die. The simulations assume the die, mandrel and container to be rigid bodies and ignore the temperature change induced during the extrusion process. Under various extrusion conditions, the present numerical analysis investigates the effective stress and profile of product at the exit. The relative influences of the friction factors, the temperature of billet and the eccentricity of four-hole displacement are systematically examined. The simulations focus specifically on the effects of the friction factor, billet temperature and eccentricity ratio of the four-hole die on the maximum load and effective stress induced within the billet and the taper angle of the extruded tubes. The simulation results provide a useful insight into the optimal processing conditions for the four-hole indirect extrusion of seamless titanium alloy tubes.     

Microstructure and texture evolution in Mg–1 %Mn–Sr alloys during extrusion

Microstructure and texture evolution in Mg–1 %Mn–Sr alloys during extrusion has been investigated. At 350 °C, the extrusion of Mg–1 %Mn (M1) alloy exhibits the progressive formation of basal texture from the undeformed zone to the die opening. The extruded microstructure of M1 consists of recrystallized grains nucleated by grain boundary bulging and elongated parent grains along with extensive twinning. At 350 °C, the extrusion of M1–1.6Sr alloy results in progressive elongation of Mg–Sr precipitates in the form of stringers from the undeformed zone to the die opening. The final extruded microstructure of this alloy shows extensive recrystallization occurring at the intermetallic stringers by particle-stimulated nucleation (PSN). M1–(0.3–1.6)%Sr alloys display weaker textures due to PSN which creates new grains with random orientations. At 250 °C, the extrusion of M1 creates necklace of small recrystallized grains around large elongated parent grains. M1–1.6Sr alloy extruded at 250 °C exhibits continuous dynamic recrystallization (CDRX) in the Mg matrix and PSN at Mg–Sr precipitates. PSN is less extensive at lower temperature. Both CDRX and PSN grains have random orientations, and therefore, alloy develops random texture.     

Extrusion of EN AW-2014 alloy in semisolid state

Abstract

The potential of forming EN AW-2014 alloy in semisolid state was investigated. The EN AW-2014 slugs were partially melted at 610°C, to a liquid fraction of ～15%, before they were extruded into a solid bar with a diameter of 16 mm. The ram speed used in this process was much lower than that employed in thixoforging of the same alloy to maximise heat removal from the slug and to fully solidify the liquid fraction by the time the extruded bar exits the die. The high solid fraction employed was also of help in this regard. Forming during extrusion under these conditions took place largely via rotation of the α-Al globules over one another, producing a remarkable microstructure of predominantly uniform globular α-Al grains. The forming load was at least an order of magnitude smaller with respect to that measured during hot extrusion of the same alloy, underlining the benefits of extruding the hard to form 2XXX alloys in semisolid state. Having been largely drained of its liquid, the final part of the preheated slug, however, failed to enjoy extrusion under such favourable conditions. The large extrusion deformation and temperatures well above the liquidus point have led to dynamic recrystallisation, which is responsible for the equiaxed, instead of fibrous, grain structure in this region.     

Comparison between mechanochemical effect on die cast and extruded magnesium alloys

Abstract

The mechanochemical effect (MCE) of several magnesium based alloys, obtained by both die casting and extrusion methods, was studied by potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. The mechanochemical behaviour of each alloy was evaluated as a function of die cast parameter, environment, and alloy composition. Electrochemical tests were performed in a buffer solution of sodium tetraborate, (Na₂B₄O₇) with and without magnesium hydroxide (Mg(OH)₂). The MCE was correlated with the microstructure of the Mg alloys.     

Untersuchungen über das Strangpressen kubisch-flächenzentrierter Metalle. Teil II: Kraftbedarf und Kraftverteilung

Investigation of the extrudability of face-centred cubic metals Part II: During continuous extrusion at certain intervals dry oxides are discharged. This is explained with the aid of rheological investigations. If a shearing device according to DIN standard is used the results may show errors in a range of 70% and more. A new device is described which avoids this source of error. The shear strength of high purity aluminium was determined at various temperatures and rates of deformation. Investigations were conducted under similar conditions on the extrusion of aluminium and a relationship between shear strength and power requirement was established. On this basis the power requirement to extrude new alloys may be predicted by comparing the shear strength of this alloy with the shear strength of an alloy whose extrudability is known. Direct extrusion experiments under isothermal conditions were conducted in the reduction range R = 1.2–300. The linear relationship in double logarithmic scale exists only in the range of R = 4–40. Indirect extrusion experiments also showed a linear relationship below the reduction rate R = 4 in a logarithmic scale. It was found that during indirect extrusion a dead metal zone is also formed and this explains the divergence of the found pressure distribution from the theoretical values. The normal pressure of the container was measured at a number of points at various temperatures and reduction rates. In the range of 150°–170°C peculiar unsteadiness occured. Normal pressure on the change of the velocity of extrusion was investigated with the aid of a stepped-down die and a strong dependence was found. A device was developed to compare the plasticity of cubic face centered metals, and it was found that the maximum plasticity is reached at 90% of the melting point in degrees absolute. Efficiency investigations during extrusion showed that the power consumption required to overcome the radial shear in continuous extrusion is 60% to 77%, whereas the power required to overcome the total shear in extrusion in a piston driven press is 94% to 87%. Extrusions inside a calorimeter showed, on the basis of mechanothermodynamic conversion, that 85% to 94% of the power was used for the deformation of the metal.     

Effect of electrolyte temperature on the polarization characteristics of an Al-Li-Cu-Mg alloy in NaOH

The effect of electrolyte temperature on the polarization characteristics of an Al-Li alloy of composition Al-1·90 Li-1·80 Cu-1·00Mg-0·09Zr in 0·1 M NaOH solution was studied by the potentiodynamic polarization method. The electrolyte temperature was the equilibrium temperature established due to the prevailing weather conditions at different times in the year. The alloys exhibited active-passive behaviour at all the temperatures. It was found that the temperature of electrolyte affected the polarization behaviour of the alloys. The zero current potential and the open circuit potential were nobler with decreasing temperature. The corrosion current density, critical current density and passive current density increased with temperature, indicating the activated nature of the electrochemical process. The passive range was higher at 35°C compared to other temperatures. The temperature effect on polarization behaviour has also been explained by considering the dissolved oxygen concentration in the electrolyte at different temperatures. The ennoblement of Cu on the Al-Li alloy surface has also been addressed.     

Effect of Equal Channel Angular Extrusion on the Microstructures and Properties of Two Extruded Al-Mg-Si Alloys

1.IntroductionAl-Mg-Si(6xxx)alloys make up nearly90%of alu-minium extrusion alloys[1].Chemical composition andheat treatment technique play important roles in gov-erning microstructure,extrudability and the mechani-cal properties of extrusions[2~12].A complete sequen-tial heat-treatment and thermo-mechanical processing(TMP)for6xxx series extrusion alloy is comprised ofhomogenisation,solution treatment,extrusion and age-ing.T5(see below)is a widely accepted post-extrusiontreatment in industry…     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.     

Improvement of mechanical properties and corrosion resistance of biodegradable Mg–Nd–Zn–Zr alloys by double extrusion

Mg–Nd–Zn–Zr alloy is a novel and promising biodegradable magnesium alloy due to good biocompatibility, desired uniform corrosion mode and outstanding corrosion resistance in simulated body fluid (SBF). However, the corrosion resistance and mechanical properties should be improved to meet the requirement of the biodegradable implants, such as plates, screws and cardiovascular stents. In the present study, double extrusion process was adopted to refine microstructure and improve mechanical properties of Mg–2.25Nd–0.11Zn–0.43Zr and Mg–2.70Nd–0.20Zn–0.41Zr alloys. The corrosion resistance of the alloys after double extrusion was also studied. The results show that the microstructure of the alloys under double extrusion becomes much finer and more homogeneous than those under once extrusion. The yield strength, ultimate tensile strength and elongation of the alloys under double extrusion are over 270 MPa, 300 MPa and 32%, respectively, indicating that outstanding mechanical properties of Mg–Nd–Zn–Zr alloy can be obtained by double extrusion. The results of immersion experiment and electrochemical measurements in SBF show that the corrosion resistance of Alloy 1 and Alloy 2 under double extrusion was increased by 7% and 8% respectively compared with those under just once extrusion.     

Influence of Ageing Heat Treatment on the High Cycle Fatigue of an 8090 Al-Li Alloy

Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.     

Magnesium – der Zukunftswerkstoff für die Automobilindustrie?

Magnesium – future material for automotive industry? Magnesium alloys show a very high potential in automotive applications as constructive metal, whereas the main focus lies on die cast parts. Electronic industry is the major commercial consumer for die castings besides the automobile industry. Room temperature applications like steering wheels and frame components in cars as well as mobile phone‐ or notebook housings are well established. These castings are produced with AZ‐ or AM‐magnesium alloys, which show good room temperature properties and a good castability. The great alloy development challenge in extending the use of magnesium cast alloys are application for higher temperatures. The application in powertrain components is considered to be the benchmark here. Besides alloy development there are also further research activities in development of casting processes. Semi‐solid processes like New‐Rheocasting (NRC), Thoxomolding ? or Thixocasting (TC) are adapted to the requirements of newly developed alloys. Not only cast alloys but also magnesium wrought alloys have moved to the centre of interest in the last decade. Alloy development for improving the formability on the one hand as well as process development in extrusion or rolling has to be done in order to find optimum parameters for deforming magnesium alloys properly.     

Mg-3Zn-1Zr合金细径管材的挤压模具设计

基于Mg-3Zn-1Zr合金本构方程运用Defrom-3D软件对多种Mg-3Zn-1Zr合金细径管材的挤压模具参数的配合进行了有限元模拟分析。结果表明:挤压模入口圆角半径一定时,挤压模模角越大,挤压杆的载荷越小,挤压模圆锥段发生紊流现象越严重,挤压死区越大。挤压模入口圆角处的磨损最为严重,当挤压模模角为120°,挤压模入口圆角半径为2 mm时,模具磨损最小,挤压载荷和模具应力也较小。工作带长度超过4 mm时,随着工作带长度的增加,模具磨损深度显著增大,管材与模具易产生黏结,进而产生缺陷和变形不均匀。采用模拟优化的模具挤压出的Mg-3Zn-1Zr合金细径管材表面质量良好、尺寸精度高,说明基于Deform-3D有限元分析能够为实际模具设计与镁合金型材的生产提供可靠参考。     

The elastic modulus of aluminium-lithium alloys

Young's modulus measurements have been made on Al-Li alloys containing up to 32 at % lithium, in an attempt to determine the cause of the high modulus that characterizes this potentially important alloy system. In alloys of commercial interest (7–11 at %, 2–3 wt % lithium) the modulus is in the range 79 to 83 GPa, the actual value depending on heat-treatment conditions. The major contribution to this increased modulus arises from lithium in solid solution. The Young's moduli of the Al₃ Li and AlLi intermetallic phases are estimated to be 96 GPa and 105 GPa respectively. Additions of magnesium to the Al-Li system produce a small decrease of the modulus, e.g. 4.5 at % (4 wt %) magnesium reduces the modulus by approximately 2 GPa.     

Nd:YAG激光焊接对铝锂合金组织和织构的影响

采用Nd:YAG激光进行了5A90铝锂合金薄板的对焊实验,借助光学显微镜、扫描电镜及EDS能谱、背散射衍射技术测试了焊缝的显微组织、合金元素分布及焊缝中的微观织构,并与母材进行了比较。结果表明:Nd:YAG激光焊接使5A90铝锂合金的微观组织和微观织构发生了很大的变化。焊缝区呈现出大量的等轴枝晶组织,这是由于焊缝中存在较多的异质形核点和较高的成分过冷度。焊缝中织构呈随机分布的状态,激光焊接完全改变了母材面心立方金属的冷轧织构组织。