Mg和半固态加工对A356合金显微组织和抗蠕变性能的影响(英文)

研究Mg和半固态加工对A356合金蠕变性能的影响。结果表明:位错攀移控制的蠕变是占主导地位的蠕变机制,它不会受到半固态加工以及进一步添加Mg的影响。Mg提高合金的抗蠕变性能主要是由于在枝晶间区域形成大量汉字型的Mg2Si。半固态加工的样品表现出比铸造样品更好的抗蠕变性能,这是由于Mg在α(Al)相中显著溶解所致堆垛层错能的减少而导致的。

Ca对铸态AZ61镁合金显微组织和压入蠕变行为的影响（英文）

研究含1%和3%(质量分数)Ca的AZ61镁合金的显微组织和蠕变性能。用压痕法研究在423~491K、200~500MPa应力作用下的蠕变性能。AZ61合金的显微组织包含α(Mg)基体相和Mg17Al12金属间化合物相。结果表明,在AZ61合金中加入Ca可通过形成(Mg,Al)2Ca相从而减少Mg17Al12相含量,当Ca含量达到3%时,形成(Mg,Al)2Ca相,Mg17Al12相消失。Ca的加入可以改善AZ61合金的蠕变性能,这是由于Mg17Al12相减少而形成的(Mg,Al)2Ca相具有高的热稳定性。根据蠕变数据可以推断,管扩散-攀移控制的位错蠕变是主要的蠕变机制,Ca添加对此机制没有影响。预变形对AZ61+3%Ca合金蠕变性能的影响表明,合金的抗蠕变性能取决于(Mg,Al)2Ca相的连续性,该相的连续性越低,合金的抗蠕变性能就越差。

The plurality effect of topographical irregularities on site seismic response

Topography can have signifi cant eff ects on seismic ground response during an earthquake because topographic irregularities cause considerable diff erences between the seismic waves emitted by the source and the waves reaching the ground surface. When a seismic motion happens in a topographically irregular area, seismic waves are trapped and refl ected between the topographic features. Therefore, the interaction between topographies can amplify seismic ground response. In order to reveal how interaction between topographies infl uences seismic response, several numerical fi nite element studies have been performed by using the ABAQUS program. The results show that topographic features a greater distance between the seismic source and the site would cause greater seismic motion amplifi cation and is perceptible for the hills far away from the source and the ridges. Also, site acceleration response is impacted by surrounding topography further than site velocity and displacement response.

Assessing the seismic behavior of steel moment frames equipped by elliptical brace through incremental dynamic analysis(IDA)

Incremental dynamic analysis and nonlinear static pushover analysis are carried out on a performance-based design to determine the seismic demands and capacities of an elliptic braced moment resisting frame(ELBRF).The objective is to assess ductility,overstrength and response modification factors in a modern steel-braced structural system based on incremental dynamic analysis.This integrated system is connected to a beam and column with an appropriate length while providing enough architectural space to allow for an opening without having the common problems associated with architectural spaces in braced systems.Several different classes of buildings are considered on soil type II.Linear dynamic analysis,nonlinear static pushover analysis and incremental nonlinear dynamic analysis related to 12 records from past earthquakes are carried out using OpenSees software.The factors of ductility,overstrength and response modification are calculated for this system.The values of 9.5 and 6.5 are found and suggested only for the response modification factor for ELBRF systems in allowable stress and ultimate limit state methods,respectively.The fragility curves are plotted for the first time for this type of bracing,which contributes to the assessment of building seismic damage.

涂层厚度对消失模铸Al-Si-Cu合金铸件的影响(英文)

对Al-Si-Cu合金进行消失模铸造,研究涂层厚度对Al-Si-Cu合金铸件缺陷、孔隙率和共晶硅间距的影响。结果表明,提高涂层浆料黏度和延长浸渍时间对铸件的完整性和显微组织有影响。薄的涂层有利于模腔充填性能的改善、显微组织的细化和低孔隙度高质量铸件的获得。

径向压力辅助充液拉深锥形杯的工艺窗口图（英文）

起皱和破裂是锥形杯成形过程中的主要缺陷。径向压力辅助充液拉深是一步成形筒形件的板材液压成形技术。获得了径向压力辅助充液拉深Al1050-O、纯铜和DIN1623 St14钢板的工艺窗口图。该工艺窗口图可快速评估板材液压成形零件的可制造性。采用有限元方法对径向压力辅助充液拉深进行模拟,并研究压力路径和原始材料及其厚度的影响。通过实验对模拟结果进行验证。结果表明:对于初始厚度较薄和强度较高的板材,其成形性更好,最终产品的的厚度分布也更均匀。所得工艺窗口图可以预测在不同加载路径下合适的加工区间以及破裂或起皱的可能性。

Effect of extrusion process on microstructure and mechanical and corrosion properties of biodegradable Mg-5Zn-1.5Y magnesium alloy

The effect of extrusion temperature and ratio on the microstructure, hardness, compression, and corrosion behavior of Mg-5Zn-1.5Y alloy were analyzed in this study. The microstructural observations revealed that the cast alloy consists of α-Mg grains, and Mg3Zn6Y and Mg3Zn3Y2 intermetallic compounds, mostly located on the α-Mg grain boundaries. Extruded alloy at higher temperatures showed coarser grain microstructures, whereas those extruded at higher ratios contained finer ones, although more dynamic recrystalized grains with lower intermetallics were measured at both conditions. Combined conditions of the lower temperature (340°C) and higher ratio (1:11.5) provided higher compressive strengths. However, no significant hardness improvement was achieved. The extrusion process could decrease the corrosion rate of the cast alloy in simulated body fluid for over 80% due to primarily the refined microstructure. The extrusion temperature showed a more pronounced effect on corrosion resistance compared to the extrusion ratio, and the higher the extrusion temperature, the higher the corrosion resistance.

影响消失模铸造Al-Si-Cu合金薄壁铸件质量的显著性工艺参数(英文)

通过控制消失模铸造工艺参数可以制备出无缺陷的形状复杂的铸件产品。对Al-Si-Cu合金消失模铸造进行研究,考察浇注温度、涂料黏度、振动时间、型砂粒径以及它们之间的交互作用对铸件表面质量、孔隙率和共晶硅间距的影响。采用两水平全因子实验设计方法考察影响铸件性能的显著性影响工艺参数。结果表明,浇注温度和振动时间对铸件共晶硅间距和孔隙率的影响最明显。在细型砂模和较高的浇注温度下,铸件的表面质量几乎保持稳定不变,而在粗型砂模下铸件的表面质量较低。涂料黏度对铸件性能没有显著影响。

双层锥形杯的水力深拉（英文）

径向压力辅助水力深拉是一项先进的板材成形技术,具有拉伸比高,表面质量好和尺寸精度高等优点。在拉伸过程中,底面和外边都受到水力的压力,因此变形均匀,失效可能性减小。与传统变形工艺相比,水力深拉技术更容易成形复杂形状的多层板材。破裂是板材成形过程中主要的不可逆的失效形式,破裂预测对确定和优化合适工艺参数具有重要作用。采用理论模型计算了径向压力辅助水力深拉成形双层锥形杯的临界破裂压力。讨论了其他参数如冲头半径、拉伸比、摩擦因数、板材厚度和材料性能等对临界破裂压力的影响。将所建模型与有限元模拟进行比较,并在Al1050/St13双层板材上进行试验验证,结果表明,试验结果与分析结果一致。

固溶处理对可生物降解Mg-6Zn合金腐蚀性能的影响（英文）

对可生物降解二元Mg-6Zn合金进行固溶处理,来评价获得的显微组织变化对合金降解速率的影响及其相关机理。在350°C条件下固溶处理6-48 h。采用光学显微镜、扫描电镜、能量色散X射线光谱仪和X射线衍射仪分析铸态和固溶处理后试样。在37°C的模拟体液中进行浸泡和电化学测试,评价其抗腐蚀性。为保证腐蚀测试的结果,对p H值进行测试。结果发现,大于24 h的固溶处理,金属间化合物相溶解于基体中,并产生了近单晶相组织。金属间化合物相的减少导致阴极区/阳极区比减小且腐蚀率降低。电化学和失重测试结果表明,延长固溶处理时间可提高合金的抗腐蚀性。经350°C固溶处理24 h后,铸态合金的抗腐蚀性提高了60%以上。另外,逐渐减少的金属间化合物相和伴随的低p H值上升,降低了腐蚀速率。对于Mg-Zn合金作为生物可降解移植材料的应用,固溶处理是一种可以提高腐蚀性的工艺。

Optimization of plasma electrolyte oxidation process parameters for corrosion resistance of Mg alloy

Plasma electrolyte oxidation(PEO)is a surface treatment method with high dependency on the process parameters.This paper focuses on maximizing the corrosion resistance of PEO coatings applied on Mg-5Zn-0.4Ca(ZX504)alloy by optimizing the process parameiers.For this purpose,the Taguchi method based on LI8 orthogonal array with mixed level design was used for optimization and determining effective parameters.Main process factors including electrolyte concentration,current density,frequency and duty cycle were considered at different levels.The corrosion resistance,as the performance indicator,was obtained using electrochemical impedance spectroscopy technique.Surface characteristics were also evaluated using SEM(scanning electron microscopy),EDS(energy dispersive spectroscopy),profilometer and contact angle goniometer.The statistical analysis showed that the optimum condition could be obtained at a current density of 200 mA/cm^2,frequency of 500Hz and at a duty cycle of 30%,in an electrolyle containing 15 g/L NazPO·12H2O and 10g/L KF.

石蜡相变材料作42CrMo4钢的热处理淬火介质

采用石蜡相变材料作为42CrMo4合金热处理的淬火介质,并与用水、空气和CuO掺杂石蜡作淬火介质进行比较。根据ASTME8M?98标准制备拉伸试样,将试样在电阻炉中加热至830°C,然后保温4 h,再在上述介质中淬火。根据得到的应力?应变曲线确定弹性模量、屈服强度、极限抗拉强度、伸长率和韧性模量。此外,还研究了不同介质热处理后的硬度和显微组织演化。石蜡与CuO掺杂石蜡淬火样品的极限抗拉强度(分别为1439和1306 MPa)高于在水(1190 MPa)和空气(1010 MPa)中淬火样品的。CuO掺杂石蜡淬火样品的硬度最高,为HV552。显微组织研究表明,非淬火钢具有铁素体/珠光体组织,而在水、石蜡和CuO掺杂石蜡中淬火,可获得铁素体/马氏体组织;还观察到,以空气为淬火介质,形成贝氏体/马氏体/铁素体三相组织。

Effect of inlet temperature and equivalence ratio on HCCI engine performance fuelled with ethanol:Numerical investigation

A numerical model is presented to investigate the performance of homogeneous charge compression ignition(HCCI) engines fueled with ethanol. Two approaches are studied. On one hand, two-step reaction mechanisms with Arrhenius reaction rates are implemented in combustion chemistry modeling. On the other hand, a reduced mechanism containing important reactions of ethanol involving heat release rate and reaction rates compatible with experimental data is employed. Since controls of combustion phenomenon and ignition timing are the main issues of these engines, the effects of inlet temperature and equivalence ratio as the controlling factors on the operating parameters such as ignition timing, burn duration, in-cylinder temperature and pressure of HCCI engines are explored. The results show that the maximum predicted pressures for thermodynamic model are about 71.3×10~5 Pa and 79.79×10~5 Pa, and for chemical kinetic model, they are about 71.48×10~5 Pa and 78.123×10~5 Pa, fairly comparable with corresponding experimental values of 72×10~5 Pa and 78.7×10~5 Pa. It is observed that increasing the initial temperature advances the ignition timing, decreases the burn duration and increases the peak temperature and pressure. Moreover, the maximum temperature and pressure are associated with richer mixtures.

Effect of thermomechanical treatment on microstructure and hardness behavior of AZ63 magnesium alloy

Due to their high specific strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two different thermomechanical treatments （TMTs）. For the first TMT, after solution treated at the temperature of 380 ℃ for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ℃and 250 ℃ for 3, 9 and 25 h. In the second TMT, the specimens were solution treated at the temperature of 380 ℃ for 20 h, underwent 2% cold worked and quenched in water of 0 ℃. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of fine β-phase （MglTA112） in the alloy matrix. The results also reveal that, the best hardness from the first TMT was produced by specimen that was pre-aged at 150 ℃ whereas, in the second TMT, aging at 250 ℃ exhibited the best hardness values.

Mg-5Zn-1Y-xCa合金的显微组织表征及挤压温度对其生物降解行为的影响（英文）

研究不同钙含量(0.0%、0.1%、0.5%和1.0%,质量分数)的铸态和热挤压态Mg-5Zn-1Y合金的显微组织和生物降解行为,挤压温度分别为300、330和370°C。研究合金的化学成分、相组成、显微组织和生物降解行为。宏观和微观检测表明,钙的加入细化了晶粒结构,形成了金属间化合物相Ca2Mg6Zn3。热挤压过程使金属间化合物相破碎为细小颗粒,并沿挤压方向分布。而且,几乎所有的合金中都发生了动态再结晶,且在370°C挤压的合金中形成了更多的双态组织。极化曲线显示无钝化区,表明活性极化在合金中占主导地位,因此,通过添加钙使晶粒细化和通过热挤压发生动态再结晶会增加合金的生物降解速率。研究结果表明,铸态Mg-5Zn-1Y-0.1Ca合金的耐腐蚀性最好,而在挤压态合金中,300°C挤压的Mg-5Zn-1Y-0.5Ca合金表现出最低的生物降解速率。因此,热挤压并非总是能改善镁合金的生物降解行为。

Organo-silane compounds in medium density fiberboard:physical and mechanical properties

We studied the effects of nanoparticles of organo-silane（NOS） compounds in the size range of20–80 nm on physical and mechanical properties in medium density fiberboard,and used NOS at four consumption levels of 0,50,100,and 150 g kg-1dry wood fibers.Density of all treatments was kept constant at 0.67 g cm-3.The water-repellent property of organo-silane significantly reduced water absorption（WA） and thickness swelling but mechanical properties declined due to the reduced proportion of wood-fiber as organo-silane was added to the matrix：the compression ratio of MDF panels and the integrity among wood-fibers both declined,resulting in reduced mechanical properties.We recommend use of 50 g of NOS/kg wood-fiber to improve WA and thickness swelling while retaining acceptable mechanical properties.

固溶处理对挤压Mg-0.35Y-2.17Nd-0.36Zr生物医用合金高温变形行为的影响（英文）

通过在225~525℃、应变速率0.0003~0.03 s-1的条件下进行压缩试验,研究挤压Mg-0.35Y-2.17Nd-0.36Zr(质量分数%)生物医用合金的高温变形行为。为了研究溶质元素的影响,变形前对材料进行固溶处理。固溶处理后,挤压态材料的低温屈服强度明显降低。当温度升高到450℃时,由于晶界滑移(GBS)的促进作用,固溶化合金的强度发生剧烈的变化。结果表明,滑移-孪生转变温度不一定与强度下降温度一致。在本构方程的基础上,结合与应变相关的材料常数,确定实验合金的变形参数和相应的活化能。对所建模型的可预测性进行验证,结果表明,实验数据与预测数据吻合较好。

挤压参数对生物植入应用镁合金降解性能的影响:综述

作为新一代临时生物材料,镁合金具有良好的生物相容性和生物可降解性,也有助于损伤骨组织的修复。但是,其在人体体液中不具备所要求的耐腐蚀性能。挤压等热机械加工对镁合金的力学性能和生物腐蚀行为均有影响。本文综述挤压参数(挤压比和温度)对镁合金生物腐蚀性能的影响。它们的影响主要归因于挤压合金显微组织的改变,包括最终的晶粒尺寸和均匀度、织构以及第二相的尺寸、分布和体积分数。挤压过程中的动态再结晶和晶粒细化使组织更均匀,并导致基面织构的形成,从而提高镁合金的强度和耐腐蚀性能。挤压温度和挤压比是影响降解的重要因素。随着挤压比的增加和/或挤压温度的降低,镁合金的晶粒尺寸减小,与挤压方向平行的样品两侧的基面织构增强,析出相体积分数降低,晶粒尺寸减小,这些都有助于提高镁合金植入物的耐腐蚀性能。

添加Ca对Mg-4Sn合金组织演变和蠕变性能的影响

通过压入蠕变试验,研究Ca添加量(最高达4%,质量分数)对Mg-4Sn合金的显微组织和蠕变性能的影响。压入蠕变试验的操作温度为445~475K,归一化应力(σ/G,σ为应力;G为剪切模量)为0.0225~0.035。利用光学显微镜和扫描电子显微镜对样品的显微组织进行研究。结果表明,Ca的加入量大于2%(质量分数)可抑制较不稳定Mg Sn2相的形成,从而使晶界处形成热稳定性较高的Ca-Mg-Sn相和Mg2Ca,提高Mg-4Sn合金的抗蠕变性能。根据压入蠕变试验所得的应力指数(6.04<n<6.89)和激活能(101.37 k J/mol<Q<113.8 k J/mol)可得出结论:管扩散攀移控制的位错蠕变是合金主要的蠕变机制。

Forced oscillations and stability analysis of a nonlinear micro-rotating shaft incorporating a non-classical theory

In this paper,the stability and bifurcation analysis of symmetrical and asymmetrical micro-rotating shafts are investigated when the rotational speed is in the vicinity of the critical speed.With the help of Hamilton's principle,nonlinear equations of motion are derived based on non-classical theories such as the strain gradient theory.In the dynamic modeling,the geometric nonlinearities due to strains,and strain gradients are considered.The bifurcations and steady state solution are compared between the classical theory and the non-classical theories.It is observed that using a non-classical theory has considerable effect in the steady-state response and bifurcations of the system.As a result,under the classical theory,the symmetrical shaft becomes completely stable in the least damping coefficient,while the asymmetrical shaft becomes completely stable in the highest damping coefficient.Under the modified strain gradient theory,the symmetrical shaft becomes completely stable in the least total eccentricity,and under the classical theory the asymmetrical shaft becomes completely stable in the highest total eccentricity.Also,it is shown that by increasing the ratio of the radius of gyration per length scale parameter,the results of the non-classical theory approach those of the classical theory.