Effect of Initial Microstructure Prior to Extrusion on the Microstructure and Mechanical Properties of Extruded AZ80 Alloy with a Low Temperature and a Low Ratio

Magnesium(Mg)alloys are the lightest metal structural material for engineering applications and therefore have a wide market of applications.However,compared to steel and aluminum alloys,Mg alloys have lower mechanical properties,which greatly limits their application.Extrusion is one of the most important processing methods for Mg and its alloys.However,the effect of such a heterogeneous microstructure achieved at low temperatures on the mechanical properties is lacking investigation.In this work,commercial AZ80 alloys with different initial microstructures(as-cast and as-homogenized)were selected and extruded at a low extrusion temperature of 220℃and a low extrusion ratio of 4.The microstructure and mechanical properties of the two extruded AZ80 alloys were investigated.The results show that homogenized-extruded(HE)sample exhibits higher strength than the cast-extruded(CE)sample,which is mainly attributed to the high number density of fine dynamic precipitates and the high fraction of recrystallized ultrafine grains.Compared to the coarse compounds existing in CE sample,the fine dynamical precipitates of Mg17(Al,Zn)12form in the HE sample can effectively promote the dynamical recrystallization during extrusion,while they exhibit a similar effect on the size and orientation of the recrystallized grains.These results can facilitate the designing of high-strength wrought magnesium alloys by rational microstructure construction.

Correlation between the Low-Temperature Photoluminescence Spectra and Photovoltaic Properties of Thin Polycrystalline CdTe Films

A dominant intrinsic luminescence band, which is due to the surface potential barriers of crystalline grains, and an edge doublet, which arises as an LO-phonon repetition of the e-h band, has been revealed in the low-temperature photoluminescence spectra of fine-grained obliquely deposited films. Doping film with In impurity leads to quenching of the doublet band, while further thermal treatment causes activation of the intrinsic band, the half-width and the blue shift of the red edge of which correlates with the maximum value of anomalously high photovoltage generated by the film.

Influence of size of seed grains and sintering condition on varistor properties of ZnO-Bi_2O_3-TiO_2-Sb_2O_3 ceramics

Varistor ceramics of ZnO Bi 2O 3 TiO 2 Sb 2O 3 system have been fabricated by introducing pre fabricated ZnO seed grains with different size distributions respectively. The results show that the varistor properties were significantly influenced by the size of introduced seed grains, and introducing larger seed grains is more advantageous to the modification of microstructure and the improvement of varistor properties. The varistor properties were considerably improved with a moderately increased sintering temperature or time, whereas degraded apparently when the sintering temperature or time was excessively increased. Compared with the sintering time, the sintering temperature plays a more critical role in determining the varistor properties. By introducing pre fabricated ZnO seed grains into the original powders, low voltage ZnO varistor ceramics possessing the desired electrical properties have been produced with a sintering temperature of about 1 210 ℃ and a sintering temperature of 2～2.5 h. [

Enhancement of room-temperature magnetoresistance in La_(0.5)Sm_(0.2)Sr_(0.3)MnO_3/(Ag_2O)_(x/2)

La0.5Sm0.2Sr0.3MnO3/（Ag2O）x/2 （x = 0.00, 0.04, 0.08, 0.25, 0.30） samples were prepared by the solid-state reaction method, and their transport behaviors, transport mechanism, and magnetoresistance effect were studied through the measurement and fitting of p-T curves. The results show that the element Ag takes part in reaction when the doping amount is small. Ag is mainly distributed at the grain boundary of the host material and is in metallic state when the doping amount is relatively large; then the system becomes a two-phase composite. A small amount of Ag doping can apparently increase grain-boundary magnetoresistance induced by the spin-dependent scattering. The resistivity of the sample doped with 30 mol% Ag is one order of magnitude smaller than that of low-doped samples, and its magnetoresistance in the magnetic field of 0.5 T and at 300 K is strengthened apparently reaching 9.4%, which is connected not only with the improvement of the grain-boundary structure of the host material but also with the decrease of material resistivity.

Groove Design and Microstructure Research of Ultra-Fine Grain Bar Rolling

New flat-oval groove rolling process of multi-direction deformation is proposed to manufacture ultra-fine grain bar. Application of new groove series can introduce uniform large plastic strain into whole cross section of the material, and meanwhile satisfy the requirements of shape and size. Principle of grain refinement, based on experimental research of small specimen, is that grain refinement of ferrite is mainly dynamic recrystallization when low-carbon alloy steel is at low temperature deformation. Relationship of grain size and z-factor is also obtained through experimental research, as well as ultra-fine ferrite grain less than 1 micron. To predict strain, shape, dimensions and grain size of the material in rolling process, numerical simulation model of the warm groove bar rolling process is established via nonlinear finite element method, and distribution of grain size of the final section is obtained via finite element subroutine. The result indicates that ultra-fine grain bar rolling can accomplish at low temperature region.

The Properties of YSZ Electrolyte Sintering at 1300 ℃

The properties of yttria stabilized zirconia（YSZ） related to the sintering process were discussed.YSZ nano-powders about 40-100 nm as raw material,the sub-micrometer grain sizes such as 0.4-3 μm in YSZ were gotten by sintering process at 1300 ℃,which was performed at 1000 ℃ for 2 h,then raised the temperature at the rate of 50 ℃ / h to 1400 ℃,then decreased directly to 1300 ℃ in 30 minutes,finally at 1300 ℃ for 5-20 hours.The ratio of bigger grain size becomes larger as the holding time increasing at 1300 ℃.The grains less than 1 μm are about 50%,eg,43.2%,52.2% and 51.1% related to 1300 ℃ holding 5 hours,8 hours and 10 hours,respectively.As YSZ grain size became small,the electrical conductivities did not decrease,even increased,about 0.20 s/cm at 1000 ℃.The reduced sintering temperature and time were benefited to co-fire with the electrodes in electrode-supported SOFCs.

Microstructure refinement and second phase particle regulation of Mo-Y_(2)O_(3) alloys by minor TiC additive

The oxide dispersion strengthened Mo alloys(ODS-Mo)prepared by traditional ball milling and subsequent sintering technique generally possess comparatively coarse Mo grains and large oxide particles at Mo grain boundaries(GBs),which obviously suppress the corresponding strengthening effect of oxide addition.In this work,the Y_(2)O_(3) and TiC particles were simultaneously doped into Mo alloys using ball-milling and subsequent low temperature sintering.Accompanied by TiC addition,the Mo-Y_(2)O_(3) grains are sharply refined from 3.12 to 1.36μm.In particular,Y_(2)O_(3) and TiC can form smaller Y-Ti-O-C quaternary phase particles(~230 nm)at Mo GBs compared to single Y_(2)O_(3) particles(~420 nm),so as to these new formed Y-Ti-O-C particles can more effectively pin and hinder GBs movement.In addition to Y-Ti-O-C particles at GBs,Y_(2)O_(3),TiOx,and TiCx nanoparticles(<100 nm)also exist within Mo grains,which is significantly different from traditional ODS-Mo.The appearance of TiOx phase indicates that some active Ti within TiC can adsorb oxygen impurities of Mo matrix to form a new strengthening phase,thus strengthening and purifying Mo matrix.Furthermore,the pure Mo,Mo-Y_(2)O_(3),and Mo-Y_(2)O_(3)-TiC alloys have similar relative densities(97.4%-98.0%).More importantly,the Mo-Y_(2)O_(3)-TiC alloys exhibit higher hardness(HV0.2(425±25))compared to Mo-Y_(2)O_(3) alloys(HV0.2(370±25)).This work could provide a relevant strategy for the preparation of ultrafine Mo alloys by facile ball-milling.

Controlled Rolling and Cooling Process for Low Carbon Cold Forging Steel

Effect of controlled rolling and cooling process on the mechanical properties of low carbon cold forging steel was investigated for different processing parameters of a laboratory hot rolling mill. The results show that the specimens with fast cooling after hot rolling exhibit very good mechanical properties, and the improvement of the mechanical properties can be attributed mainly to the ferrite-grain refinement. The mechanical properties increase with decreasing final cooling temperature within the range from 670 ℃ to 570 ℃ due to the finer interlamellar spacing of pearlite colony. The specimen with fast cooling after low temperature rolling shows the highest values of the mechanical properties. The effect of the ferrite grain size on the mechanical properties was greater than that of pearlite morphology in the present study. The mechanical properties of specimens by controlled rolling and cooling process without thermal treatment were greatly superior to that of the same specimens by the conventional rolling, and their tensile strength reached 490 MPa grade even in the case of low temperature rolling without controlled rolling. It might be expected to realize the substitution medium-carbon by low-carbon for 490 MPa grade cold forging steel with controlled rolling and cooling process.

粮仓能源桩系统绿色储粮技术应用研究

简化粮食入库后全周期控温供冷储粮流程,提出满仓主动降温与夏季粮仓热平衡2种供冷方案。通过理论公式计算2种方案下的供冷量需求,并利用有限元模拟软件计算得出能源桩换热量,由此设计可满足上部粮仓供冷需求的能源桩运行方案。结果表明:在1万t储粮规模下,粮仓能源桩储粮技术可满足2种供冷方案下的能源需求,对比谷物冷却机与地源热泵储粮,其初期投入成本更低;对比空调储粮,其初期投入成本增加,但能源桩储粮技术可利用绿色清洁能源,储粮能耗最低。

Analytical Investigation of Prior Austenite Grain Size Dependence of Low Temperature Toughness in Steel Weld Metal

Prior austenite grain size dependence of the low temperature impact toughness has been addressed in the bainitic weld metals by in situ observations.Usually,decreasing the grain size is the only approach by which both the strength and the toughness of a steel are increased.However,low carbon bainitic steel with small grain size shows a weakening of the low temperature impact toughness in this study.By direct tracking of the morphological evolution during phase transformation,it is found that large austenite grain size dominates the nucleation of intragranular acicular ferrite,whereas small austenite grain size leads to grain boundary nucleation of bainite.This kinetics information will contribute to meet the increasing low temperature toughness requirement of weld metals for the storage tanks and offshore structures.

小晶粒高硅铝比NaY分子筛低温合成研究

采用自制的偏铝酸钠为合成导向剂,在低温下水热晶化合成出了小晶粒高硅铝比的NaY分子筛。考察了合成导向剂的陈化温度、陈化时间、晶化碱度、晶化温度和晶化时间对产品的影响,得到了制备NaY分子筛最佳的工艺条件,并进行了放大制备。在此条件下,NaY分子筛结晶度(峰面积)≥90%,结晶度(峰高)≥85%,硅铝比≥5.5,晶粒尺寸均在(100~200)nm,不仅优于工业标样的指标要求,且易于放大。

固体发动机药柱低温点火开裂失效的跨尺度分析

为了准确预测推进剂装药在低温点火过程中是否发生开裂,提出了一种全局⁃局部单向收缩耦合的跨尺度分析方法。针对高能硝酸酯增塑聚醚(NEPE)推进剂,开展低温中应变率单轴拉伸试验,获取了推进剂的典型失效模式。结果表明,基于发展的推进剂非线性粘弹性本构模型,实现了固体发动机药柱低温点火的宏观结构分析,获取了推进剂药柱结构危险点的位置;同时建立了考虑颗粒与基体界面脱湿和颗粒断裂的细观颗粒填充模型,进一步将宏观结构分析结果作用于相应的细观代表性体积单元(RVE)上。最后,建立推进剂细观失效准则,表明在低温点火条件下药柱结构完整性满足要求。收缩跨尺度分析方法可作为预测药柱在低温点火过程中开裂行为的有效手段。

结实期不同时段低温对粳稻生长发育和产量的影响

为探索结实期不同时段低温对粳稻生长发育和产量的影响,试验以4份优质粳稻品种为试材,在开花后7~13、14~20、21~27 d分别进行低温处理(昼/夜:17℃/13℃),以室外常温种植为对照,测定水稻剑叶的SPAD值、抗氧化物酶活性、干物质积累量、穗部性状及产量。结果表明:不同品种生理和产量性状存在一定差异,同时对结实期低温的响应也不同。结实前、中、后期低温处理后,剑叶的SPAD值较对照分别显著增加7.74%~13.49%、20.09%~33.17%,29.65%~52.36%。低温总体上提高了剑叶的抗氧化物酶活性,且前期低温对其影响高于后期。前期低温处理后4个品种的穗干物质重分别显著降低28.48%、35.44%、33.51%、33.30%,茎干物质重受低温影响较小。低温胁迫对二次枝梗的影响高于一次枝梗,均不同程度降低一、二次枝梗的穗粒数、千粒重和结实率,最终降低水稻产量(0.35%~17.49%)。研究结果可为寒地粳稻耐冷生理研究提供理论参考。

基于溶液除湿的新型粮食干燥设备设计及特性分析

我国每年因粮食霉变等原因造成的损失巨大,粮食干燥是实现安全储藏的重要环节之一。另外,随着对粮食品质要求的不断提高,低温通风除湿干燥成为一个主要发展方向。溶液除湿技术相比于冷凝法去湿,具有除湿效果好、温湿度控制精确、节能等优势,应用日益广泛。该设计以“绿色、健康、生态”粮食储藏为理念,开发了基于溶液除湿的新型粮食干燥设备,并通过实验,对机组性能进行了分析。实验证明,不同环境空气工况下,机组出口空气参数达到了设计要求。该系统以电能驱动,并利用冷凝废热驱动溶液循环,系统制冷性能系数(coefficient of refrigeration performance,COPC)可达4.20以上、除湿性能系数(dehumidification coefficient,COPD)不低于3.1,与冷凝法低温干燥机相比可节能50%以上,与烘干机相比可节能20%左右,节能效果显著。从环保、储粮品质的提升、系统节能考虑,该设备具有较大优势,市场应用前景广阔。

光伏离网供电空调控温储粮技术应用

光伏离网供电空调控温储粮系统由光伏发电板、智能控制器、光伏空调和能源管理系统组成。智能控制器通过智能补偿、智能控制算法,实现光伏和市电双电源无缝切换,优先使用光伏,实现光伏零浪费,光伏直驱空调直接利用光伏板发的直流电来驱动机组,达到节能降耗的目的。解决了制冷空调用电费用高、光伏发电投资成本高和投资回收期长的问题。显著降低了空调控温的运行成本,实现了储粮空调控温的“零”碳或低碳的绿色储粮技术。

基于动态隔热阻断的低温储粮靶向通风控温系统设计与试验

针对传统低温储粮系统效能低、功能单一、精细化管控不足等问题,基于动态隔热阻断理论,创新研发低温储粮靶向通风控温系统。该系统主要包括温度监测、决策控制、驱动执行和远程监控等模块,可实现自主化智慧联动靶向通风控温作业。为验证系统的实用性和有效性,从控温性能、储粮品质等方面进行综合评价。结果表明:在1年试验周期内,全仓均温低于14.2℃,最高粮温低于20℃,水分降低0.2%,脂肪酸值增幅为1.4(KOH/干基)/(mg/100g),相较传统低温储粮控温系统脂肪酸值增幅降低41.7%,且无虫霉发生发展,具有较好的控温性能和品质保持性。系统化解决因储藏局部发热、盲目通风、冷心热皮等问题而造成储粮经济损失,达到高标准低温储粮技术要求。

低温破碎及装药结构对内弹道性能影响的数值分析

以大口径火炮密实装药发射安全性为背景,对火药颗粒低温破碎及装药结构对内弹道特性的影响进行了数学建模和仿真分析。针对中心点传火管结构的大口径火炮密实装药,建立传火管及装药床的双一维两相流数学模型,结合膛内火药颗粒应力及破碎度函数,采用数值差分方法对内弹道过程进行数值仿真,研究火药温度及混合装药方案对火药颗粒破碎度及火炮内弹道性能的影响。结果表明,在低温条件下,单一装药结构火药颗粒将发生破碎,且破碎度随温度降低而增大,在-20℃和-40℃条件下,最大破碎度分别达到1.896和2.487,膛内压力分别为690.32MPa和803.64MPa,增幅达到16.4%;在总装药质量6.25kg不变的条件下,小颗粒药装药质量从0增至0.4kg,最大破碎度从2.487减至1.803,膛内压力从803.64MPa减至740.81MPa,由此可见混合装药结构可以有效避免火药颗粒的破碎。

升温温度对CuAlMnNi记忆合金晶粒尺寸及性能的影响

研究了低温循环热处理工艺中的升温温度对CuAlMnNi记忆合金板材组织及性能的影响。结果表明,随着升温温度的提高,在550℃退火30 min的析出相α的体积分数和最大尺寸均先增大后减小,平均尺寸不断增加;后续高温退火的晶粒尺寸先增大后减小,合金试样的超弹性先升高后降低,残余应变先减小后增大,且晶粒尺寸越大,启动相变的临界强度越小。其原因是升温温度影响晶界活动性B与α相的析出,进而改变后续高温退火时的晶粒尺寸;晶粒尺寸的增大会降低晶界对马氏体相变的阻碍,提高合金的变形能力,进而表现出对合金板材超弹性的提高和残余应变的降低。

拔节期低温对小麦结实特性的影响及追施氮肥的缓解效应

为明确氮肥对拔节期低温小麦结实粒数与粒重的影响,以小麦品种‘华成3366’为材料进行盆栽试验,在拔节期进行持续5 d(LT-T1)和10 d(LT-T2)的低温胁迫处理,以自然温度为对照(CK-LT),并在低温胁迫结束当天追施氮肥(LT-N),对盆栽小麦的穗部性状、小穗发育和小花发育进行比较分析。结果表明:与CK-LT相比,随着低温时间的延长,LT处理下的穗数、穗粒数、粒重、总小穗数和总小花数降幅逐渐增大,而顶部结实小花数、基部结实小花数、强势结实小花数和弱势结实小花数均明显下降,其中基部结实小花数和弱势结实小花数下降幅度最大。与LT相比,随着低温时间的延长,LT-N处理下的穗粒数、穗数、粒重、总小穗数和总小花数升幅逐渐增大,不同穗位小花数之间相比发现顶部结实小花数、基部结实小花数、强势结实小花数、弱势结实小花数均有所增加,其中基部结实小花数和弱势结实小花数增加幅度最大。综上,拔节期低温主要通过减少基部结实小花数和弱势结实小花数,降低小花结实率,进而减少穗粒数和弱势粒重。低温后追施氮肥主要通过增加基部结实小花数和弱势结实小花数,提高基部小花和弱势小花结实率,增加基部小花和弱势小花对穗粒数的贡献率,进而增加穗粒数和弱势粒重,降低低温胁迫引起的产量损失。

微合金化重型热轧H型钢横向低温冲击稳定性研究与控制

对重型热轧H型钢低温冲击性能的影响因素进行了分析,结果表明,重型H型钢的加热温度及轧制温度不合理导致内部晶粒不均匀是引起低温冲击性能不合格的主要原因。通过现场工艺的优化,改善了重型热轧H型钢的低温冲击韧性,提高了产品合格率。