触变模锻成形工艺对镁合金成形件力学性能的影响

采用半固态等温热处理法、近液相线模锻法和等通道角挤压法制备AZ91D-Y镁合金半固态坯料。分别将3种状态的坯料加热到半固态温度区间进行二次重熔后,进行了触变模锻成形。结果表明,在半固态温度为560℃,模锻压力为200MPa的条件下,半固态等温热处理法、近液相线模锻法和等通道角挤压法制备坯料分别保温30,20,15min后触变模锻获得最佳力学性能;随着坯料加热温度的升高,触变模锻成形件力学性能呈现先上升后下降的趋势;增加成形压力有利于触变模锻成形件力学性能的提高;在相同成形条件下,等通道角挤压法制备坯料触变模锻后的力学性能最好,近液相线模锻法次之,半固态等温热处理法较差。     

AlSi7MgBe合金的半固态挤压成形

对采用近液相线半连续铸造技术制备的AlSiTMgBe合金坯料进行半固态挤压成形,通过组织与性能的分析,研究了AlSi7MgBe合金的半固态挤压成形性.结果表明:用近液相线半连续铸造技术制备的AlSiTMgBe合金坯料具有均匀,细小的蔷薇状组织,在575℃对其二次加热可获得稳定的、适合于半固态触变成形的球化组织,进行半固态挤压成形可获得表面光洁,组织细小,分布均匀的成形件,在540℃固溶5 h然后175℃时效10 h处理,其抗拉强度为325 MPa,伸长率为14.6%,表明具有良好的半固态挤压成形性.     

液相线模锻法制备ZK60-RE镁合金半固态组织演变

给出了液相线模锻法制备ZK60-RE镁合金半固态坯料的实验方法和工艺参数,并研究了该方法制备的ZK60-RE镁合金在半固态等温热处理过程中的微观组织演变.结果表明:利用液相线模锻法可以制备半固态ZK60-RE镁合金坯料,半固态ZK60-RE镁合金坯料在保温时间较短的半固态等温热处理过程中能形成晶粒细小、晶粒粗化速度较为缓慢的球晶组织,晶粒在600℃保温15 min、610℃保温3 min和618℃保温0 min时分别达到最小,最小尺寸分别为35、45、30 μm,能够达到半固态加工实际化生产的较高要求.晶粒在不同的温度下随着保温时间的延长,晶粒的圆整度均逐渐变小,球晶化越来越好.     

Semi–solid thixo-extrusion of AlSi7MgBe alloy

对采用近液相线半连续铸造技术制备的AlSi7MgBe合金坯料进行半固态挤压成形, 通过组织与性能的分析, 研究了AlSi7MgBe合金的半固态挤压成形性. 结果表明: 用近液相线半连续铸造技术制备的AlSi7MgBe合金坯料具有均匀、细小的蔷薇状组织, 在575℃对其二次加热可获得稳定的、适合于半固态触变成形的球化组织, 进行半固态挤压成形可获得表面光洁, 组织细小、分布均匀的成形件, 在540℃固溶5 h然后175℃时效10 h处理, 其抗拉强度为325 MPa, 伸长率为14.6%, 表明具有良好的半固态挤压成形性.     

AZ91D镁合金托弹板半固态触变模锻研究

为了掌握半固态触变模锻中工艺参数对成形零件的微观组织和力学性能的影响规律,借助拉伸试验机和金相显微镜对AZ91D镁合金托弹板的半固态触变模锻过程进行了研究.AZ91D镁合金半固态坯料分别采用传统SIMA法和新SIMA法制备.结果表明:压力对托弹板零件的充型过程有很大影响,当压力为500 kN,托弹板零件充型不满;当压力为2000 kN,托弹板零件充型良好.坯料加热温度和保温时间对托弹板零件的力学性能有一定影响.当压力为2000 kN,模具预热温度为450 ℃,坯料在545 ℃保温20 min时,新SIMA法制备的半固态坯半固态触变模锻成形的托弹板零件获得最佳的力学性能.与传统SIMA法相比,新SIMA法制备的半固态坯成形的托弹板零件的室温力学性能和100℃的高温力学性有很大提高.     

ZL201合金液相线铸造与二次加热的合金组织

为了研究半固态金属的成型规律,采用电子显微镜及图像分析仪,研究了近液相线半连续铸造ZL201合金的微观组织及其在二次加热过程中的变化.研究表明,在液相线温度下半连续铸造的ZL201合金组织为均匀、细小的蔷薇状组织,晶粒的平均等积圆直径为43.6μm,晶粒平均圆度为1.88.经二次加热后,铸造组织逐渐转变为等轴晶.在620℃下加热20min后,晶粒平均等积圆直径为111μm,晶粒平均圆度1.42.在640℃下加热20min后,晶粒平均等积圆直径为108μm,晶粒平均圆度1.58.研究表明,近液相线半连续铸造可以获得理想的ZL201合金半固态坯料.     

超声波搅拌及等温热处理对ZL101合金半固态组织的影响

采用超声波搅拌和等温热处理制备ZL101合金半固态坯料,研究了超声波搅拌处理和等温热处理中等温温度、等温时间等工艺参数对ZL101半固态组织形貌的影响。研究结果表明:超声波搅拌可有效细化和球化组织,消除组织缺陷;适当的等温处理可以明显改善半固态ZL101的凝固组织;当等温温度为590℃、等温时间为30min时,半固态ZL101合金中初生α-Al相细化和球化效果最明显;初生α-Al相的平均等积圆尺寸达到157μm,形状因子达到0.87。     

铝合金半固态成形技术及设备

在国家“863”计划的支持下,北京科技大学和兄弟单位合作研制开发的铝合金半固态成形技术及设备已经成熟,研制的电磁搅拌制备铝合金半固态坯料连铸设备可以制造直径为50～100mm的铝合金非枝晶半固态连铸棒料,研制的感应加热技术可以将铝合金非枝晶坯料快速加热到固液两相区,半固态坯料温度差可控制在1～2℃之内,研制的铝合金半固态成形技术可成形各种铝合金零件毛坯,该项目已经通过国家“863”计划组织的专家委员会的验收。目前制备铝合金半固态连铸坯料的最佳工艺是电磁搅拌方法,该工艺制备的半固态连铸坯料纯净,不易卷入气体,控制方便,产…     

半固态浆料制备技术发展现状

半固态成形技术与传统成形技术相比,以其诸多的优点日益受到越来越多研究者的关注.在半固态成形技术的研究中,制备具有非枝晶组织的理想半固态浆料(坯料)是关键.将半固态浆料制备工艺分为两大类:液态金属半固态浆料制备和固态金属半固态坯料制备,并分别介绍了两类工艺中常用的几种工艺方法.电磁搅拌法和应变诱化激活法已有工业化应用;双螺旋搅拌法和半固态等温热处理法等比较有发展潜力;其他多种方法各有特点,可用于特定合金或者特定工作条件下的研究开发.     

A356合金近液相线半固态铸造非枝晶组织与模锻成形性能

采用近液相线铸造技术制备出具有等轴晶粒的半固态A356合金坯料,合适的铸造工艺为铸造温度615℃、铸造速度160mm/min、液面深度220mm、冷却水流量0.1m3/min;在电阻炉加热的条件下,半固态A356合金坯料的重熔加热温度场均匀,合适的加热制度为保温温度585℃,保温时间10min。在模具温度为300℃~500℃条件下,触变模锻成形了汽车轮毂件,经T6热处理后的抗拉强度为215.65MPa,延伸率为14.45%,硬度为78.66HV,该研究结果对半固态加工技术在汽车零部件生产领域的应用有积极意义。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.