AZ31镁合金板材自动氩弧焊接工艺研究

利用六轴焊接机器人夹持氩弧焊枪进行AZ31镁合金自动氩弧焊接工艺研究,焊后利用金相显微镜、扫描电子显微镜、X射线衍射仪和万能试验机等对焊接接头进行微观组织表征及力学性能测试。结果表明,在焊接电流160 A、焊接速度0.45 m/min、填丝速度0.6 m/min、钨极针与板材距离0.5 mm（前半段）和2.0 mm（后半段）以及保护气体流量16 L/min（正面）和21 L/min（背面）的条件下,能得到外观形貌良好、质量可靠的AZ31镁合金焊接接头。焊接接头的金相组织显示,焊缝区微观组织可清晰地分为母材区,热影响区和熔化区。焊接过程在热影响区和熔化区出现了大量的沉淀相,X射线衍射结果表明,该沉淀相为β Mg17Al12沉淀相。拉伸结果显示,焊接接头的抗拉强度达到了母材的81.02%,在断口观察到了大量的解离面和韧窝的存在,呈现出脆性断裂与韧性断裂相结合的混合断裂特征。     

Ca对AZ31镁合金CO_2激光焊接接头组织和性能的影响

采用添加填充材料的CO2激光焊接工艺对AZ31镁合金薄板进行焊接,研究了不同Ca含量对焊缝金属的显微组织和力学性能的影响.结果表明:当激光功率为1 500W,焊接速度为3 m/min时,AZ31镁合金CO2激光焊接的焊缝金属中添加一定量的σCa0.19%元素,可以得到成分相对较均匀、组织细小的焊缝.当填充带材为AZC04(焊缝中Cσa=0.19%)时,焊缝区晶粒相对细小,析出相细小弥散,此时焊接接头的力学性能最优,焊接效率基本可达到100%.     

M42/X32异种金属CO2激光焊接接头组织和性能的研究

利用CO2激光器对双金属带锯条齿部用高速钢钢丝M42及背部用高强度钢带X32进行焊接,通过金相显微镜,扫面电镜(SEM),显微硬度仪,电子探针(EPMA)等手段研究了焊后高速钢M42与高强度钢X32焊接接头组织演变规律,焊接接头合金元素分布,以及不同焊接工艺对异种金属焊接接头组织及力学性能的影响.研究表明：随着焊接速度的增大,焊缝中心区等轴晶增多,树枝晶减少,且靠近M42侧熔合边界区的等轴晶更细小;各种工艺条件下焊接接头硬度均较母材高,且靠近M42侧的熔合区的硬度要高于焊缝区的硬度.当焊接功率为2 754 W,焊接速度为14 m/min时,焊接接头的性能优良,抗弯强度值达到112 MPa,达到了双金属带锯条的焊接性要求.     

焊接速度对铝合金搅拌摩擦焊接头性能的影响

以厚度3 mm的6061-T6铝合金板材搅拌摩擦焊对接接头为研究对象,建立热力耦合有限元模型,准确模拟了焊接过程的温度场分布及演变规律,采用光学显微观察、电子背散射衍射、显微硬度测量以及拉伸试验等表征方法,研究了焊接速度对焊接接头成形特性、显微组织和力学性能的影响机理.结果表明:接头焊核区在焊接过程中经历了完全动态再结晶,形成细小等轴晶;后退侧热影响区经历了动态回复,晶粒显著长大,晶界强化作用弱于焊核区晶粒;当焊接速度为300～800 mm/min时,接头焊缝成形良好,拉伸断裂均在焊缝后退侧热影响区,在焊接过程中受温度(400～480℃)影响显著,析出强化相溶解导致力学性能明显降低,在此焊接速度范围内,随速度的提高,接头强度增加,最高强度系数为80.86％(800 mm/min);当焊接速度进一步增加至1200 mm/min时,接头的焊接成形性变差,焊核区出现未焊合和隧道缺陷,接头拉伸试验时在焊核区发生断裂.     

高温扩散对过共晶Al-Si合金组织的影响

研究w(Si)=20%的过共晶Al-Si合金在高于共晶点温度进行热处理后的组织形貌变化.结果表明:热处理温度610℃,保温时间分别为5、10、15min时,随保温时间的延长,粗大的柱状树枝晶α-Al变为近球状组织;不规则的多边形状和花瓣状的初晶Si会逐渐熔断、钝化,最后以15μm小块状和近球状组织出现;粗大的针片状共晶Si先发生熔断变为细小的颗粒状,然后全部熔化,最后在水淬中析出细小颗粒状和纤维状的共晶Si包围α-Al相;热处理温度580℃,保温时间分别为5、15、30、40min时,随保温时间的延长,初晶硅尺寸变细小,直径达到30μm,圆整度不断得到提高,当保温时间达到40min时,共晶硅变为纤维状.     

AZ31B镁合金TIG和MIG焊接接头组织性能比较分析

研究了AZ31B镁合金钨极氩弧焊(TIG)和熔化极氩弧焊(MIG)焊接接头组织及性能。在厚度为8.0 mm的AZ31B镁合金板材上分别进行了填丝TIG和MIG两种焊接试验,分析了AZ31B镁合金两种焊接工艺以及接头焊缝的微观组织和显微硬度。试验结果表明,填丝TIG焊缝成形良好;MIG焊接时有飞溅现象,焊缝成形不及TIG均匀。TIG和MIG焊接接头的相组成与母材的相组成一致。MIG焊接热影响区HAZ的晶内析出相弥散分布,焊缝区晶界析出相连续分布;而且MIG焊接接头的显微硬度值较TIG焊接时要高,焊接接头的力学性能有所提高。     

AZ31镁合金薄板的交流钨极氩弧焊

探讨了氩弧焊工艺参数对镁合金焊接接头质量的影响，采用金相显微镜，对AZ31镁合金薄板TIG焊接接头进行了微观组织观察、用X-射线衍射仪等分析测试手段对相组成和力学性能进行了分析，结果发现：焊接电流为40A和45A时，焊接接头的力学性能最好，(σb为205MPa)，为母材强度的80％左右，断裂总是发生在热影响区，焊缝区组织呈细小的等轴晶，主要存在α-Mg和Mg17Al12两种相，热影响区组织较粗大。     

高速列车车厢用的铝合金板焊接接头的组织与性能

利用光学显微镜和透射电子显微镜研究了国产7020铝合金熔化极惰性气体保护焊(MIG)接头的微观组织结构,并对接头的力学性能进行研究.结果表明,接头的硬度以焊缝中心线为轴呈对称分布,且焊缝中心为接头的最薄弱环节;焊缝区为典型的树枝状晶的铸造组织.在熔合区,焊缝一侧为沿散热方向排列的柱状晶,另一侧为细小的等轴晶组织.热影响区内,仍可见纤维状加工痕迹,部分析出相固溶到基体中;强化相的粗化,是热影响区内出现软化区的主要原因.国产7020铝合金焊接接头强度达到欧洲标准.     

焊接工艺对7N01P铝合金激光-MIG复合焊接接头中气孔的影响

铝合金在激光-熔化极惰性气体保护（melt inert-gas,MIG）复合热源焊接过程中形成的气孔会引起应力集中、降低焊接接头的强度和塑性等问题,从而明显降低焊接接头的性能。采用激光-MIG复合热源焊接技术,对4 mm厚7N01P铝合金进行了对接焊接,分析了焊接工艺对焊接接头中气孔的影响。结果表明,采用复合热源焊接技术,在送丝速度为7.0、8.0、9.0 m/min,焊接速度为0.9、1.0、1.1 m/min,功率分别为2.3、2.4、2.5 kW时均可以实现7N01P 铝合金板材的单面焊双面成形。当激光功率为2.3 kW,送丝速度为9.0 m/min,焊接速度为1.0 m/min时,焊接接头中的气孔数量最少,气孔率约为1.2%。此外,激光功率的变化会影响焊接接头中气孔的形成,随着激光功率从2.3 kW增加到2.5 kW时,气孔数量先增加后下降;送丝速度的变化也会影响焊接接头中气孔数量,当送丝速度由7.0 m/min增加至9.0 m/min时,气孔数量有所降低;而焊接速度对焊接接头中气孔的影响是双向的,随着焊接速度的增加,气孔数量先减少（焊接速度从0.9 m/min到1.0 m/min）后增加（焊接速度在1.1 m/min）。可见,工艺参数的优化可以起到减少焊接接头中气孔的作用。     

硬质合金YG8与D6A异种金属CO_2激光焊接接头组织和性能的研究

利用CO_2激光器对双金属带锯条齿部用硬质合金YG8及背部用超高强度钢D6A进行焊接,通过金相显微镜,扫描电镜(SEM),显微硬度仪,电子显微探针(EPMA)等手段研究了焊后硬质合金YG8与超高强度钢D6A焊接接头组织演变规律,焊接接头合金元素分布,以及不同焊接工艺对异种金属焊接接头组织及力学性能的影响.研究表明,随着焊接速度增大,焊缝中心区等轴晶增多,树枝晶减少,且靠近YG8侧熔合区的等轴晶更细小;各种工艺条件下焊接接头硬度均较母材高,且靠近YG8侧的熔合区的硬度要高于焊缝区的硬度.当焊接功率为3 960 W,焊接速度为9m/min时,焊接接头的性能优良,抗弯强度值达到349 MPa,达到双金属带锯条的焊接性能要求.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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