Impact of 3D/4D methods on the understanding of recrystallization

In this paper, we discuss the impact that non-destructive 3D (x,y,z) and 4D (x,y,z,time) X-ray experimental methods have had on the understanding of recrystallization of deformed metals. Well-planned experiments on nucleation and grain boundary migration are reviewed with focus on information gained, which could not have been obtained by traditional 2D or destructive 3D methods. It has also been found that the 3D/4D X-ray measurements sometimes happen to reveal phenomena, which were not expected and therefore not planned to investigate. Examples of this are also reviewed here. Finally, the implications of the new findings for modelling of recrystallization are discussed, key experiments for the future are suggested and the needs for technique advancements are summarized, all seen from the recrystallization perspective.     

Influence of undissolved second-phase particles on dynamic recrystallization behavior of Mg-7Sn-1Al-1Zn alloy during low-and high-temperature extrusions

This study investigates the effects of fine and coarse undissolved particles in a billet of the Mg-7Sn-1Al-1Zn (TAZ711) alloy on the dynamic recrystallization (DRX) behavior during hot extrusion at low and high temperatures and the resultant microstructure and mechanical properties of the alloy.To this end,partially homogenized (PH) and fully homogenized (FH) billets are extruded at temperatures of 250 and 450 ℃.The PH billet contains fine and coarse undissolved Mg2Sn particles in the interdendritic region and along the grain boundaries,respectively.The fine particles (＜1 μm in size) retard DRX during extrusion at 250 ℃ via the Zener pinning effect,and this retardation causes a decrease in the area fraction of dynamically recrystallized (DRXed) grains of the extruded alloy.In addition,the inhomogeneous distribution of fine particles in the PH billet leads to the formation of a bimodal DRXed grain structure with excessively grown grains in particle-scarce regions.In contrast,in the FH billet,numerous nanosized Mg2Sn precipitates are formed throughout the material during extrusion at 250 ℃,which,in turn,leads to the formation of small,uniform DRXed grains by the grain-boundary pinning effect of the precipitates.When the PH billet is extruded at the high temperature of 450 ℃,the retardation effect of the fine particles on DRX is weakened by their dissolution in the α-Mg matrix and the increased extent of thermally activated grain-boundary migration.In contrast,the coarse Mg2Sn particles in the billet promote DRX during extrusion through the particle-stimulated nucleation phenomenon,which results in an increase in the area fraction of DRXed grains.At both low and high extrusion temperatures,the extruded material fabricated using the PH billet,which contains both fine and coarse undissolved particles,has a lower tensile strength than that fabricated using the FH billet,which is virtually devoid of second-phase particles.This lower strength of the former is attributed mainly to the larger grains and/or absence of nanosized M2Sn precipitates in it.     

管道断面尺寸对真空管道交通建设成本与运营成本的影响

影响真空管道交通建设成本与运营成本的因素很多,其中管道断面尺寸是最主要的影响因素。管道断面越小,显然建设成本越低。但小管道断面意味着阻塞比增加和空气阻力增大,对运营成本的影响并非显然。通过对真空管道中不同阻塞比、不同真空度时列车空气阻力的计算与比较,可知对于相同的空气阻力工况,减小断面所节省的抽真空能耗大于因提高真空度而增加的抽真空能耗。因此,当不考虑真空度提高所造成的维持真空成本的增加时,减小管道断面既是降低真空管道交通建设成本的有效途径,也是降低真空管道交通运营成本的有效途径。     

热端管长度对涡流管性能影响的试验研究

涡流管具有结构简单、无运动部件、价格低廉、可靠性高等优点,但管内发生的能量转换却极为复杂。本文以压缩空气为工作介质,对涡流管能量分离特性进行试验研究,获得涡流管制冷、制热效应随热端管长度、冷端流率之间的关系。研究结果表明,热端管长度越长,六流道喷嘴涡流管的制冷、制热效应越好,获得最大制冷效应时的冷端流率越大。     

Impact of friction stir welding on recrystallization of oxide dispersion strengthened ferritic steel

Oxide dispersion strengthened (ODS) steels can be used as the structural materials in the future fusion reactors and the fuel cladding materials in the advanced fission reactors. However, the weldability of ODS steels is a severe problem. In the present study, defect-free joints of the 15Cr-ODS ferritic steel were achieved by friction stir welding at different rotation speeds. The recrystallization, hardness and tensile properties are highly related with the rotation speed of the stir tool. The higher rotation speed results in coarser grains in the top SZ, while the grain size exhibits more complicated relation with the rotation speed in the SZ center. The joint welded at 250 rpm exhibits a maximum tensile strength of 974 MPa that reaches about 84% of that of the base metal.     

Influence of resonance tube length on performance of thermoacoustically driven pulse tube refrigerator

A resonance tube is an important component of a thermoacoustic engine, which has great influence on the performance of the thermoacoustically driven pulse tube refrigerator. A standing wave thermoacoustic engine is simulated with linear thermoacoustics. Computed results show that an appropriate accretion of the resonance tube length may lead to a decrease of the working frequency and an increase of the pressure amplitude, which will improve the match between the thermoacoustic engine and the pulse tube refrigerator. The theoretical prediction is verified by experiments. A refrigeration temperature as low as 88.6 K has been achieved with an optimized length of the resonance tube, helium as working gas, and 2200 W of heating power.     

Comments on the extent of simultaneous recovery during recrystallization and its effect on recrystallization kinetics

Sufficient experimental evidence does exist to indicate that simultaneous recovery can contribute to the strong negative deviation from linear KJMA kinetics. The Monte Carlo simulations also demonstrate that nonuniform deformation can cause similar deviation. However, conformance of data that exhibits strong KJMA deviation to the Speich-Fisher model implies that recovery could be dominant. Furthermore, nonuniform deformation should cause copper to deviate from linear KJMA kinetics, but copper shows reasonably linear KJMA behavior. Unfortunately, current knowledge of recovery and recrystallization mechanisms is inadequate to positively isolate the relative effects of recovery and nonuniform deformation. Therefore, continued emphasis should be placed on the use of simulation studies and correlations of simulated and experimental behavior to isolate not only these effects but also other factors that affect recrystallization behavior.     

Numerical study on the performance of swirl tube based on orthogonal design

Here, an axial flow cyclone separator is design is proposed. The effects of varying the structural parameters and operating conditions on pressure drops and separation efficiency were investigated via a numerical simulation approach. The results show that of the three structural parameters considered, the distance between the diffuser and blade is the most significant factor impacting separation performance compared to the blade pitch and blade shaft diameter. Increasing the distance between conical outlet and blade can decrease its pressure drops and increase separation efficiency; while increasing the shaft diameter can increase pressure drops, and the increasing blade pitch can decrease both the pressure drop and the separation efficiency. The pressure drop of the optimized swirl tube was 102.1 Pa, with a corresponding separation efficiency of 95.04% for 100 μm particles at an extraction ratio of 10%. Further, the cut-off particle size can reach 3 μm, demonstrating that the swirl tube offers good separation performance and has the potential to be widely applied in industrial gas–solid separation applications.     

某车体6005A铝合金边梁的腐蚀失效行为研究

某列车车体吊挂牵引变流器一侧6005A铝合金边梁在检修过程中发现腐蚀严重,为探究其腐蚀原因,采用宏微观形貌观察、EDS能谱分析、金相组织分析、化学成分分析等分析手段并结合现场实际运行情况对边梁进行失效分析。结果表明：6005A铝合金边梁发生了晶间腐蚀,裂纹萌生于表面并沿晶界向内部扩展,由于边梁处于排污口附近的腐蚀环境中,在边梁局部区域表面形成了晶间腐蚀裂纹,材料局部表面基体脱落,从而使边梁腐蚀失效。     

Measured and predicted effect of flowrate and tube spacing on horizontal tube absorber performance

The presented model applies to absorption in a falling film of constant thickness of a binary mixture with only one component in the vapour phase. The mathematical formulation with partial differential equations is based on very general assumptions. The model is validated for a horizontal tube absorber. The absorber is simplified to a series of vertical falling films with mixing conditions in between. The dimensionless absorber operating conditions are: Gz = 0.1–10, Le = 0.002 or 0.004, Λ = 0.01 or 0.02, Bi ≈ 5, θ_c ≈ −0.2, N_c = 0.1. The absorber consists of 10 cooled tubes, measurements were obtained at tube spacings: 0, 3, 15 and 24 mm and with sheet, droplet and jet flow in between the tubes. The correlation between predicted and measured absorption outcomes is very strong. On average the predicted outcomes equal the measured ones within the scatter, if the diffusivity is taken 0.3 times the established correlation and varies with x and y.     

6005A铝合金挤压型材搅拌摩擦焊接头的疲劳性能

对6005A-T6铝合金挤压型材进行焊速为1000 mm/min的搅拌摩擦高焊速焊接,研究了对接面机械打磨对接头组织和力学性能的影响.结果 表明,与生产中常用的焊前打磨处理相比,尽管对接面未机械打磨的接头焊核区的"S"线更明显,但是两种接头的硬度分布和拉伸性能相当,拉伸时都在最低硬度区即热影响区断裂.高周疲劳实验结果表...     

Impact of geometry on the performance of memristive nanodevices

We examined the influence of memristor geometry on switching endurance by comparing ribbed and planar TiO(2)-based cross-point devices with 50 nm × 50 nm lateral dimensions. We observed that planar devices exhibited a factor of over four improvement in median endurance value over ribbed structures for otherwise identical structures. Our simulations indicated that the corners in the upper wires of the ribbed devices experienced higher current density and more heating during device forming and switching, and hence a shorter life time.     

Impact of visual performance management systems on the performance management practices of organisations

The purpose of this paper was to explore how visual strategy and performance management techniques impact performance measurement and management practices of organisations. A novel visual performance management approach is developed and implemented in qualitative case studies with seven manufacturing SMEs across Europe. The implementation cases demonstrate that visual management systems serve to support ongoing strategy development and implementation, facilitate performance measurement and review, enable people engagement, improve internal and external communication, enhance collaboration and integration, support the development of a continuous improvement culture and foster innovation. Additional explorative and longitudinal research is required to understand the long-term impact of such approaches in both small and larger organisations.     

Effects of the prolonged vertical tube on the separation performance of a cyclone

This article aims at the gas flow into the dustbin of conventional cyclones, the prolonged cyclone (attaching a vertical tube at the bottom of the dust outlet) is proposed by some researchers, which can make flow with dust enter into the tube and separate further. The Reynolds stress transport model (RSTM) has been employed to predict the gas flow fields of the conventional and prolonged cyclones. The tangential velocity, axial velocity profiles and turbulent kinetic energy profiles are presented, and the downward flow rates into the dustbin of the three cyclones are compared. The separation performances of these three cyclones are tested. The result indicates that the tangential velocity, axial velocity and turbulent kinetic energy in the dustbin reduce greatly when the prolonged vertical tube attaching into the dust outlet, which can avoid the re-entrainment of already separated dust effectively. Furthermore, the prolonged vertical tube increases the separation space of dusts. The downward flow rate into the dustbin of the prolonged cyclone decreases compared with the conventional cyclone. The experimental results show that the prolonged vertical tube can improve the separation efficiency by a slightly increased pressure drop. However, for an even longer tube, the separation efficiency is slightly reduced. Thus, there is an optimal tube length for a given cyclone.     

Effects of magnesium on surface quality of AA6061 extrusions

Abstract

The surface quality of extruded aluminium sections is often a key characteristic in determining customer acceptance. The present paper presents the results of a study which consisted of 108 production runs of an AA6061 alloy extrusion. The volume of each run is measured as the number of 99 cm billets processed before the extrudate surface roughness exceeded a threshold value. Melt chemistry, particularly Mg, Si, and Zn content are shown to be significant in determining production volume. Scanning electron microscopy and X-ray analyses reveal that the presence and nature of MgO are the key determinant of production volume.     

Leakage effect analysis on the performance of a cylindrical adjustable inertance tube

The inertance tube plays a significant role in improving the performance of the Stirling type pulse tube cryocooler by providing the desired phase angle between the mass flow and pressure wave. The phase angle is highly depended on the inertance tube geometry, such as diameter and length. A cylindrical threaded root device with variable thread depth on the outer screw and inner screw creates an adjustable inertance tube whose diameter and length can be adjusted in the real time. However, due to its geometry imperfectness, the performance of this threaded inertance tube is reduced by the leaks through the roots between the two screws. Its phase angle shift ability is decreased by 30% with the leakage clearance thickness of 15.5 μm according to both the theoretical prediction and the experimental verification.     

Effects of reservoir volume on performance of pulse tube cooler

A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.     

车辆用6005A大型铝合金型材的研制与开发

车辆轻量化是交通运输现代化和高速化的有效途径,铝合金是车辆轻量化的理想材料.着重研讨了6005A铝合金大型材的工艺特点;大型材的铝合金体系;熔铸、挤压与热处理工艺及其优化等关键技术,为车辆用大型铝合金型材的批量生产奠定技术基础.