考虑枕下胶垫超弹性本构的弹性长枕轨道动力仿真

为揭示枕下胶垫超弹性本构特征对弹性长枕轨道动力响应的影响,基于Mooney-Rivlin超弹性本构理论,建立车辆-轨道-隧道-土体空间耦合动力学模型,分析车辆荷载作用下轨道-隧道系统的动力响应,与等效刚度法进行对比,并探讨超弹性本构中枕下胶垫的合理硬度。研究结果表明:基于超弹性本构仿真得到的轨道各位置位移、加速度数据更真实准确;随着枕下胶垫硬度减小,隧道壁加速度有效值减小,但会放大轨枕垂向位移及下部结构75 Hz频段的振动;综合考虑轨道动力响应、振动传递特性及减振效果,建议弹性长枕轨道枕下胶垫的绍尔硬度取52。

Microstructure and mechanical properties of as-quenched Mg-Gd-Zr alloys

Mg-xGd-0.6Zr （x=2, 4, 6, mass fraction） alloys were prepared by semi-continuous casting process. The effects of Gd content on the microstructures and mechanical properties of Mg-xGd-0.6Zr alloys were studied and the solid solution treatment process of Mg-6Gd-0.6Zr alloys was optimized. The microstructures and mechanical properties of all the studied alloys were analyzed by optical microscope, X-ray diffraction, scanning electron microscope equipped with energy dispersive spectroscope and micro-hardness tester. The results show that the grain size slightly decreases with increasing Gd content and there is a close linear relationship between Gd content and micro-hardness of Mg-xGd-0.6Zr alloys. The second phases Mg 2 Gd and Mg 3 Gd formed due to non-equilibrium solidification during the casting process can be transformed into equilibrium phase Mg 5.05 Gd which can dissolve into α-Mg solid solution phase at solution temperature of 460 ℃ The optimized solid solution treatment of Mg-6Gd-0.6Zr alloy is （300 ℃ 6 h） ＋ （460 ℃ 10 h）.

Mechanical properties,electrical conductivity and microstructure of CuCrZr alloys treated with thermal stretch process

CuCrZr alloys were treated with the thermal stretch process at various temperatures from 100 to 300℃.The results reveal that the thermal stretch process is successfully developed to manufacture the precipitation hardening CuCrZr alloys with a good combination of microhardness and electrical conductivity.By increasing the tensile elongations at each temperature from 100 to 300℃,the microhardness increases whereas the electrical conductivity decreases slightly.Cr-containing precipitate phases with a Nishiyama-Wasserman orientation relationship to the copper matrix were observed by TEM.The achievement of high micro-hardness and acceptable electrical conductivity in the thermal stretch treated alloys is ascribed to the interactions of the heteroatom solution,dislocation increment,grain refinement and dispersive precipitation effect.

Effects of heat treatment on microstructure and microhardness of linear friction welded dissimilar Ti alloys

A detailed investigation for the influence of post weld heat treatment （PWHT） on the microstructure of TC4 and TC17 dissimilar joints was analyzed. The fully transformed microstructure in the as-welded zone indicated that the peak temperature exceeded theβ-transus temperature at the weld interface during linear friction welding. TC4 side was mainly composed of martensiteα′phase with random distribution and it was singleβfor that of TC17. In the thermomechanically affected zones of TC4 and TC17, the structure undergoes severe plastic deformation and re-orientation, yet without altering the phase fractions. After PWHT, in the weld zone of TC4 alloy, the phase transformationα′→α＋βoccurred and the acicularαwas coarsened, which resulted in a decrease in hardness. In the weld zone of TC17 alloy, fineαphase precipitated at the grain boundary and withinβgrains, which resulted in a sharp increase in hardness.

Structure and properties of FeCoNiCrCu_(0.5)Al_x high-entropy alloy

Effects of Al content and heat treatment on the structure,hardness and electrochemical properties of FeCoNiCrCu0.5Alx high-entropy alloys were investigated.The phase structure of as-cast alloys evolves from FCC phase to BCC phase with the increase of Al content.The stable phase of FeCoNiCrCu0.5Alx high-entropy alloys will transform from FCC phase to FCC＋BCC duplex phases when x value increases from 0.5 to 1.5.The hardness of BCC phase is higher than that of FCC phase,and the corrosion resistance of BCC phase is better than FCC phase in chlorine ion and acid medium.High hardness and good corrosion resistance can be obtained in as-cast FeCoNiCrCu0.5Al1.0 alloy.

Effects of heat treatment on phase contents and mechanical properties of infiltrated B_4C/2024Al composites

The B4C/2024Al composites were successfully produced by pressureless infiltration method, and the effects of heat treatment on phase content and mechanical properties were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and mechanical properties testing. The results show that phases of BnC/2024Al composites include B4C, Al, Al3BC, AlB2 and Al2Cu. The phase species remain unchanged; however, the phase content of the composites changes significantly after heat treatment at the temperature of 660, 700, 800 or 900 ℃ for 12, 24 or 36 h. It is found that the heat treatment results in not only considerable enhancement in hardness, but also reduction in bending strength of the composites. Heat treatment at 800 ℃ for 36 h does best to hardness of the composites, while at 700 ℃ for 36 h it is the most beneficial to their comprehensive mechanical properties.

Optimization of heat treatment of gravity cast Sr-modified B356 aluminum alloy

In recent years,certain foundry processes have made it possible to obtain products with very thin parts,below the4mmthreshold of the permanent mold casting technology.The safety margins of these castings have been reduced,so the T6heattreatment conditions adopted for the Al?7Si?Mg alloys need to be investigated to identify the best combination of strength andductility.Furthermore,the cost and the production time associated with T6heat treatment have to be optimized.In the present work,an experimental study was carried out to optimize the solution treatment and artificial aging conditions in gravity cast thin bars ofB356aluminum alloy modified with Sr.Two solution temperatures were selected,530°C and550°C,respectively,with solutiontime ranging from2to8h,followed by water quenching and artificial aging at165°C with aging time from2to32h.The results ofhardness and tensile tests were correlated with differential scanning calorimetry(DSC)analysis.The best combination of mechanicalproperties and heat treatment duration was obtained with2h solutionizing at550°C and8h aging at165°C.DSC analysis showedthat the alloy’s mechanical properties reach the maximum value when theβ''phase is completely developed during the artificialaging.

Bonding interface zone of Mg-Gd-Y/Mg-Zn-Gd laminated composite fabricated by equal channel angular extrusion

In order to improve the mechanical properties and corrosion resistance of Mg alloys,the equal channel angular extrusion (ECAE)was employed to fabricate the Mg-5Gd-5Y/Mg-2Zn-1Gd(GW55/ZG21)laminated composites.After fabrication and annealing treatment,the microstructural evolution,phase constitution,microhardness,and bonding strength were investigated on the bonding interface zone of GW55/ZG21 laminated composites.The bonding interface zone of GW55/ZG21 laminated composites comprises a lot of Mg3(Y,Gd)2Zn3 particles along the bonding interface,some rod Mg24(Y,Gd)5 phases on GW55 side,and a precipitation free zone(PFZ)on ZG21 side.After annealing treatment,Mg3(Y,Gd)2Zn3 particles along the bonding interface increase, rod Mg24(Y,Gd)5 phases on GW55 side decrease,and PFZ is broadened.Meanwhile,the hardness on the bonding interface zone decreases and the bonding strength increases from 126 MPa to 162 MPa.

Properties improvement and microstructure changes during thermomechanical treatment in sintered Cu-Au alloy

The changes in hardness, microhardness, electrical conductivity and microstructure of the sintered Cu-4%Au （mole fraction） alloy during thermomechanical treatment were studied. Following the primary strain hardening, an annealing of rolled alloy in the temperature range of 60-350 ℃ provided additional strengthening due to the anneal hardening effect. An increase in properties took place in two stages, and the best combination of properties was achieved in the alloy pre-rolled with 40% reduction after annealing at 260 ℃. Significant microstructural changes followed the changes of properties in the course of the thermomechanical treatment.

Effect of Surface Treatment on Bonding Strength of Aluminum-Magnesium Hot-Rolled Composite Plate

The effect of different surface treatments on the bonding strength of composite plates was investigated under the conditions of 400℃ and reduction ratio of 45%.Results show that the wire brush grinding treatment can only eliminate the oxide film on the plate surface,but it can hardly produce a hard layer on the plate surface.The bonding effect depends on the element diffusion promoted by the close contact between the metals on both sides of the interface.After anodic oxidation,there is a hard layer on the metal surface,and the hard layer broken during the rolling process forms a mechanical occlusion at the bonding interface.However,the hard layer cannot form an effective combination with the metal at the interface,and the bonding can only occur in the fresh metal bonding area at the crack of the hard layer.The acid-alkali washing treatment can completely remove the hard layer on the surface of both alloys without increasing the surface roughness of the plate,and the metal on both sides of the interface is more closely bonded during the rolling process.The optimal bonding strength can be obtained by surface treatment of acid-alkali washing for the aluminum-magnesium hot-rolled bonding.