Thixoforming of SiC ceramic matrix composites in pseudo-semi-solid state

1INTRODUCTIONIt has great economic profit to exploit the uti-lization of SiC ceramic material for its strength,hardness,wear resistance,corrosion resistanceand high temperature resistance,abundant re-source and low price.But the brittle charactergreatly restricts its application in the field of engi-neering structure materials.Recently a series ofceramic matrix composites with exi mious perform-ance have been developed by reinforcing the matrixmaterial with other materials.Al/SiC is a la…     

动态网络中行业因素与股市波动性研究

股票市场的波动性一直是金融领域的一个研究重点,行业因素对股市波动性的影响也是投资者关注的一个焦点.从复杂网络视角出发,以行业内股票相关性强弱(RIL)为指标实证研究了行业因素与股票波动性之间的联系.研究发现不同行业的RIL指标有不同的参考标准,于是对原有的RIL指标进行了改进得到新指标RIL*.在以沪深300样本股为例的实证研究中发现采矿业、金融业和房地产业内的股票受行业因素影响最强.研究还发现股票网络结构变化和股市波动性之间存在联系,当行业因素影响急剧降低时,行业内的股票走势会猛烈上升或下降.     

Effect of Zr content on quench sensitivity of AlZnMgCu alloys

The effect of Zr content on quench sensitivity of AlZnMgCu alloys was investigated by mechanical properties testing and microstructure observations. The results show that with the increase of Zr the quench sensitivity relative to hardness and strength increases, while that relative to elongation decreases. From hardness and strength viewpoints, the low quench sensitivity is observed for the Zr-free and 0.05% Zr-containing alloys, which is quite quench sensitive from the ductility viewpoint. The largest quench sensitivity relative to hardness and strength is observed for 0.1% Zr-containing alloy, this is mainly due to large amount of high angle grain boundaries and incoherent Al3Zr dispersoids caused by recrystallization, which may efficiently promote heterogeneous precipitation during air quenching. More than 0.05% Zr can significantly decrease the quench sensitivity relative to ductility, which can be primarily attributed to recrystallization inhibiting and grain refining effects of Zr.     

Mechanism of strengthening of cube texture for high purity aluminum foils by additional-annealing

1　INTRODUCTIONHighpurityaluminumfoilsareusedastheanodematerialofhighvoltageelectrolyticcapacitorswhichneedstrongcubetexture { 0 0 1}〈10 0〉forlargeeffec tivesurfacefromchanneletching[1] .Becauseofitstechnicalimportance ,alotofeffortshavebeenmadetodevelopstrongcubetextureinhigh purityalu minumfoils[2 8] .Itwasfoundthatthecubetextureinthefoilscanbestrengthenedviaanannealingpro cessfollowedbyalowcoldrolling[7,8] ,andsuchanannealingiscalledadditional annealinginthispaper .Buttherewerefewinv…     

固溶后预析出对7A55铝合金力学及腐蚀性能的影响

采用硬度测试、电导率测试及透射电镜观察，研究固溶后降温至440℃预析出处理时间对7A55铝合金板材力学和腐蚀性能的影响。结果表明：随预析出处理时间的延长，基体析出相逐渐增多且长大，导致合金时效后硬度和强度先提高而后降低；晶界析出相逐渐长大，晶界无沉淀析出带宽化，晶界相不连续性先提高而后降低，导致合金抗晶问腐蚀和剥落腐蚀性能也先升高而后降低。     

淬火介质对7055铝合金晶界析出行为的影响

采用透射电镜研究了淬火介质对7055铝合金晶界析出相及无沉淀析出带的影响。结果表明，空气淬火时，合金冷却过程在晶界上析出η平衡相。合金经室温水淬及沸水淬火合金时效后，晶界析出相尺寸差别小，呈链状连续分布；晶界无沉淀，析出带较窄，平均宽度分别约为33nm和43nm。空气淬火合金时效后晶界析出相尺寸差别较大，呈不连续分布；晶界无沉淀，析出带很宽，约102nm。对其原因进行了分析和讨论。     

Zn含量对Al-Zn-Mg-Cu合金挤压棒材耐剥落腐蚀性能的影响

通过剥落腐蚀浸泡实验和极化曲线测试,研究了Zn含量对Al-Zn-Mg-Cu合金挤压棒材耐剥落腐蚀性能的影响,结合金相显微镜、扫描电镜、扫描透射电镜等微观组织表征方法对影响机理进行了分析和讨论。结果表明:Zn含量(质量分数)由7.93%增至9.85%时,棒材剥落腐蚀抗力下降,剥落腐蚀等级由EA变成EC,最大腐蚀深度由334 μm增至579 μm。Zn含量增加,合金中粗大第二相数量增加,时效后晶界η相尺寸和间距变小、Zn和Mg含量增加,是耐剥落腐蚀性能下降的主要原因。     

推送技术在Internet中的应用

以广播作为基本思想的推送技术在Internet中的应用改变了我们以往从Internet获取信息的方式。本文介绍了一套实现将服务器信息推送给客户机的设计方案。该方案应用了发射器、调谐器、频道等概念,利用TCP端口和套接字技术、多点传送技术及发行／订阅的思想,用Java语言实现了服务向客户机推送个性化信息的服务。用户可根据自己的兴趣爱好选择不同的频道,使信息传送向个性化、智能化方向发展。     

2024铝合金航空座椅支承零件等温模锻成形研究

采用Deform-3D有限元软件及等温模锻试验对2024铝合金航空座椅支承零件的成形过程进行了模拟与试验研究,并且分别对等温模锻件和热轧板机加工零件的组织和性能进行了对比研究。结果表明,在420℃、锻压速度为1.5 mm·s-1、保压时间为1.5~2 min的锻造工艺参数条件下,2024铝合金航空座椅支承零件锻造成形的最大锻压力为12700 k N,锻件成形金属流动顺利。在本文的工艺条件下试制锻造了多件2024铝合金航空座椅支承件,测试分析结果表明,通过等温模锻制造的航空座椅支承零件较热轧板机加工零件强度提高11.4%,最高的强度为508 MPa,且不同方向力学性能的差异小于3%。     

Cu含量对Al-9.0Zn-1.5Mg-xCu合金断裂韧性的影响

采用Kahn撕裂实验,结合金相、扫描电镜、扫描透射电镜、数字图像相关法和电子背散射衍射等手段,研究了Cu含量对Al-9.0Zn-1.5Mg-x Cu合金断裂韧性的影响规律。结果表明：随着Cu含量从0%增大到2.6%(质量分数),合金断裂韧性先逐渐增大,在Cu含量为1.0%～1.3%时达到最高值,而后大幅减小。随着Cu含量从0%增大到1.0%～1.3%,合金的再结晶晶粒面积分数逐渐增大,导致裂纹形核过程的变形量和穿过再结晶晶粒扩展的比例增大;裂纹单位面积形核功(UIE)和单位面积扩展功(UPE)逐渐增大。Cu含量为2.6%时,合金残余第二相的面积分数、晶界上部分η相的尺寸增大,导致裂纹形核过程的变形量减小;η′强化相的间距减小,导致晶内-晶界强度差和裂纹沿再结晶晶界扩展的比例明显增大;UIE和UPE均大幅减小。