轧制ZK61镁合金板材晶粒长大行为

通过对热轧的ZK61镁合金板材试样分别进行不同温度和不同保温时间的退火实验,利用金相显微镜(OM)观察显微组织,对晶粒尺寸进行分析和处理,并建立数学模型,系统研究了轧制ZK61镁合金的晶粒长大行为。研究结果表明,晶粒尺寸随着退火温度的升高与退火时间的延长而粗化,退火温度对晶粒长大的影响比退火时间的影响明显。对于ZK61镁合金在250~450℃温度区间的晶粒长大过程,其晶粒尺寸与加热时间的关系可用Beck方程D~n-D_0~n=kt描述,其中k=k_0exp[-Q_g/(RT)]。计算可得晶粒长大指数n为3.5,长大激活能Qg为45kJ/mol。     

Willingness to pay for private and public road safety in stated preference studies: Why the difference?

Estimates of the willingness to pay (WTP) for a mortality risk reduction can be used to calculate the value of a statistical life, which is a major component in many economic evaluations of environmental and safety policies. Previous research on the WTP for risk reductions using stated preference methods have found that the mean WTP for public risk reductions is significantly smaller compared to the mean WTP for private risk reductions of equal magnitude. Hence, the use of a private or public scenario in stated preference studies of e.g. environmental or safety policies may strongly determine the outcome of the economic evaluation. In this paper we use a stated preference survey to show that WTP for a private risk reduction is three times higher compared to a public risk reduction and a significant part of the difference can be explained by respondents’ attitudes towards privately and publicly provided goods in general.     

Mikrostrukturelle und mechanische Eigenschaften von laserstrahlgeschweißtem Magnesiumfeinblech AZ31‐HP mit und ohne Zusatzwerkstoffe

Microstructural and mechanical properties of laser welded sheets of magnesium AZ31‐HP with and without filler wires This paper describes Nd:YAG laser beam welding experiments carried out on rolled 2.5 mm thick magnesium sheet AZ31‐HP. For the butt welds in flat position, filler wires AZ31X and AZ61A‐F were used, diameter 1.2 mm. The microstructure and mechanical properties of the different laser beam welded joints were examined and compared with one another. The obtained results show that the laser beam welding of AZ31‐HP sheet is possible without hot crack formation, both without and with filler wires. The determined tensile strength, ductility, fracture toughness and microhardness of laser beam welded joints without filler wire were not effected by AZ31X nor AZ61A‐F. By use of these filler wires loss of zinc was minimized and the shape of weldments was optimized. The values of fracture strength, yield strength and microhardness of the joints and base material are quite similar. It is found that the ductility of the joints is lower than the base materials due to the heterogeneous microstructure of the fusion zones and geometrical notches of the weld seams. Both, weld and base material of AZ31‐HP, showed stable crack propagation. Furthermore, for base material slightly lower fracture toughness values CTOD than for the joints were determined.     

Realization of high strength and high ductility for AZ61 magnesium alloy by severe warm working

Extruded Mg–6%Al–1%Zn (AZ61) alloy bar was subjected to 4-pass Equal Channel Angular Extrusion (ECAE) processing at 448–573 K. At the processing temperature of 448 K, extremely fine grains with the average grain size of 0.5 mm are formed as a result of dynamic recrystallization originated by fine Mg₁₇Al₁₂ (b) phase particles having 50–100 nm diameter dynamically-precipitated during ECAE processing. The sizes of both α matrix and β phase decrease with decreasing processing temperatures. In tensile test at room temperature under the strain rate of 1×10^—3 s^—1, tensile strength increases with decreasing ECAE processing temperatures due to fine grains, fine precipitates and residual strain hardening. Especially, highest strength of 351 MPa was achieved in the specimen ECAE-processed at 448 K. In addition to such high strength, elongation reaches 33% in that specimen. This specimen exhibits clear strain rate dependencies of both flow stress and elongation even at room temperature. As a result, higher elongation of 67% is obtained under low strain rate of 1×10^—5 s^—1.In such specimen, non-basal slip and grain boundary sliding occur in addition to basal slip. Furthermore, there are grains with no dislocations, suggesting the occurrence of dynamic recovery. The contribution of all the deformation mechanisms would cause high ductility in fine-grained AZ61 alloy specimen with high strength.     

Biodistribution study of [^61Cu]pyruvaldehyde-bis （N-4-methylthiosemicarbazone） in normal rats as a PET tracer

[61Cu]-labeled pyruvaldehyde-bis (N-4-methylthiosemicarbazone) (61Cu-PTSM), a promising agent made for imaging blood perfusion, was produced via the natZn(p,x)61Cu nuclear reaction in a 30 MeV cyclotron, and separated by a two-step column chromatography method developed in our laboratory using a cation and an anion exchange resin. After 150μA irradiation for 76 min, about 6.006 Ci of 61Cu2 was obtained with a radiochemical separation yield of 95% and a radionuclidic purity of 99%. 61Cu-PTSM was prepared using an optimized method with in-house synthesized PTSM ligand for radiolabeling following quality control procedures using RTLC and HPLC. The tracer is mostly incorporated in heart, kidneys and brain compared to free copper cation as a control. These are in agreement with former reports. In conclusion, [61Cu]-PTSM was prepared at the radiopharmaceutical scales with high quality and is a potential PET tracer in the perfusion study of the heart, kidney, brain and tumors.     

ECS700 Profibus通信在纸机上的应用

DCS控制系统与通信技术的发展促进了工业生产水平及产品质量的提高。本文介绍了ECS700系统、Profibus通信技术。通过配置COM722模块、变频器通信卡,实现ECS700系统与ATV61变频器的Profibus通信。通过Profibus通信便可实现DCS对变频器的启动、停止、速度给定等操作。     

镁合金AZ61热流变应力模型的两种建模方法

为确定镁合金AZ61热变形特性与制定合理的成形工艺参数,利用Gleeble-1500热模拟试验机研究该材料在变形温度523K~673K和应变速率0.001s-1~1s-1下的流变应力行为。根据实验数据,确定热变形激活能,建立峰值应力与温度和应变速率的关系式。采用两种不同方法,分别建立任意时刻流变应力与温度、应变速率和应变的关系式,并验证了流变应力方程的准确性。研究结果表明,直接考虑应变对应力的影响模型相对误差为5.46%,通过动态再结晶分数间接考虑应变对应力的影响模型相对误差为5.42%,两种模型的预测值均与实验值较吻合。     

轴向力对搅拌摩擦焊接AZ61A镁合金拉伸性能的影响(英文)

研究轴向力对搅拌摩擦焊接AZ61A镁合金拉伸性能的影响。在3～7kN范围内选择5个不同大小的轴向力制备接头。测试接头的拉伸性能,并研究其与搅拌区显微组织和硬度的相关性。结果表明,与其他轴向力下的接头相比,轴向力为5kN时制备的接头具有最好的拉伸性能。搅拌区生成的细晶组织和高硬度是获得高拉伸强度的主要原因。     

基于SCA61T 的驻车坡度采集

利用SCA61T传感器对驻车坡度进行采集,并通过CAN总线实时传输至中央ECU,从而实现电子驻车系统对驻车力进行实时控制。结果表明,该系统可使停驻车辆在不同的坡度下施加合适的制力,使电子驻车系统更节能、经济,并通过减少制动机械零部件的磨损而延长使用寿命。