Evolution of mechanical properties,localized corrosion resistance and microstructure of a high purity Al-Zn-Mg-Cu alloy during non-isothermal aging

The evolution of mechanical properties,localized corrosion resistance of a high purity Al-Zn-Mg-Cu alloy during non-isothermal aging(NIA)was investigated by hardness test,electrical conductivity test,tensile test,intergranular corrosion test,exfoliation corrosion test,slow strain rate tensile test and electrochemical test,and the mechanism has been discussed based on microstructure examination by optical microscopy,electron back scattered diffraction,scanning electron microscopy and scanning transmission electron microscopy.The NIA treatment includes a heating stage from 40℃to 180℃with a rate of 20℃/h and a cooling stage from 180℃to 40℃with a rate of 10℃/h.The results show that the hardness and strength increase rapidly during the heating stage of NIA since the increasing temperature favors the nucleation and the growth of strengthening precipitates and promotes the transformation of Guinier-Preston(GPI)zones toη'phase.During the cooling stage,the sizes ofη'phase increase with a little change in the number density,leading to a further slight increase of the hardness and strength.As NIA proceeds,the corroded morphology in the alloy changes from a layering feature to a wavy feature,the maximum corrosion depth decreases,and the reason has been analyzed based on the microstructural and microchemical feature of precipitates at grain boundaries and subgrain boundaries.

Microstructure and properties of 35 kg large aluminum alloy flywheel housing components formed by squeeze casting with local pressure compensation

The squeeze casting method with local pressure compensation was proposed to form a flywheel housing component with a weight of 35 kg.The numerical simulation,microstructure observation and phase characterization were performed,and the influence of local pressure compensation on feeding of thick-wall position,microstructure and mechanical properties of the formed components were discussed.Results show that the molten metal keeps a good fluidity and the filling is complete during the filling process.Although the solidification at thick-wall positions of the mounting ports is slow,the local pressure compensation effectively realizes the local forced feeding,significantly eliminating the shrinkage cavity defects.In the microstructure of AlSi9Mg alloy,α-Al primarily consists of fragmented dendrites and rosette grains,while eutectic Si predominantly comprises needles and short rods.The impact of local pressure compensation on strength is relatively minimal,yet its influence on elongation is considerable.Following local pressure compensation,the average elongation at the compensated areas is 9.18%,which represents a 44.90%higher than that before compensation.The average tensile strength is 209.1 MPa,and the average yield strength is 100.6 MPa.The local pressure compensation can significantly reduce or even eliminate the internal defects in the 35 kg large-weight components formed by squeeze casting.

Ceramic Properties of Three Specimens of Alluvial Clays Used in Local Constructions from Mbouda Clay Deposit, West Cameroon

The Mbouda alluvial deposit is located at the foot of the Bamboutos mountains (West Cameroon) where three types of clayey materials are widespread. The populations collect these clays in their natural state in view of constructions using fired bricks or compressed blocks. Unfortunately, these buildings are not strong. This study investigates the causes of the strengthlessness of buildings and suggests solutions to overcome the difficulty. The research content includes field and laboratory studies. The methodology consists of sampling black (AN), white (AB) and red (AR) clays specimens identified in the study area and analysing them simultaneously at MIPROMALO (Cameroon) and at ACME LAB in Vancouver (Canada). The results obtained show a high sand content in the samples AN (64%), AB (55.2%), AR (30.9%). The compressive strength of the built specimens is low at 900˚C considered as the traditional firing temperature AN (0.94 MPa), AB (5.25 MPa), AR (2.18 MPa). The mineralogical series are identically made by kaolinite, chlorite, gibbsite, quartz, muscovite, biotite, goethite, magnetite and hematite. Silica (SiO2) presents higher contents AN (52.87%), AB (48.02%), AR (47.68%) followed by alumina (Al2O3) AN (29.96%), AB (28.13%), AR (24.72%). The other elements are poorly represented.

Regulating Anderson localization with structural defect disorder

Localization due to disorder has been one of the most intriguing theoretical concepts that evolved in condensed matter physics.Here,we expand the theory of localization by considering two types of disorders at the same time,namely,the original Anderson’s disorder and the structural defect disorder,which has been suggested to be a key component in recently discovered two-dimensional amorphous materials.While increasing the degree of both disorders could induce localization of wavefunction in real space,we find that a small degree of structural defect disorder can significantly enhance the localization.As the degree of structural defect disorder increases,localized states quickly appear within the extended phase to enter a broad crossover region with mixed phases.We establish two-dimensional diagrams for the wavefunction localization and conductivity to highlight the interplay between the two types of disorders.Our theoretical model provides a comprehensive understanding of localization in two-dimensional amorphous materials and highlights the promising tunability of their transport properties.

Effects of Electron Beam Local Postweld Heat Treatment on Microstructure and Properties of 30CrMnSiNi2A Steel Welded Joints

To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.

Local inhomogeneity of mechanical properties in stir zone of friction stir welded AA1050 aluminum alloy

The local inhomogeneity of the stir zone in friction stir welded face-centered cubic metal was investigated,which has multiple activated slip systems during plastic deformation,by selecting commercial AA1050 aluminum alloy as an ideal experimental material.The local inhomogeneity was evaluated by uniaxial tensile tests using small samples with a 1 mm gauge length.The corresponding microstructural parameters such as grain size,misorientation angle distribution,and micro-texture,were quantified by the backscattered electron diffraction technique.A comprehensive model was used to reveal the microstructure−mechanical property relationship.The experimental results showed that the uniaxial tensile property changes significantly across the weld.The maximum ultimate tensile strength(UTS)occurred in the center of the stir zone,which was 99.0 MPa.The weakest regions were located at the two sides of the stir zone.The largest difference value in UTS reached 14.9 MPa,accounting for 15%of the maximum UTS.The analysis on the structure−mechanical property relationship suggests that the micro-texture change with the location formed during the rotational material flow is the main reason for the local inhomogeneity.

Local spatial properties based image interpolation scheme using SVMs

Image interpolation plays an important role in image process applications. A novel support vector machines （SVMs） based interpolation scheme is proposed with increasing the local spatial properties in the source image as SVMs input patterns. After the proper neighbor pixels region is selected, trained support vectors are obtained by training SVMs with local spatial properties that include the average of the neighbor pixels gray values and the gray value variations between neighbor pixels in the selected region. The support vector regression machines are employed to estimate the gray values of unknown pixels with the neighbor pixels and local spatial properties information. Some interpolation experiments show that the proposed scheme is superior to the linear, cubic, neural network and other SVMs based interpolation approaches.

Impact vibration properties of locally resonant fluid-conveying pipes

Fluid-conveying pipe systems are widely used in various equipments to transport matter and energy.Due to the fluid–structure interaction effect,the fluid acting on the pipe wall is easy to produce strong vibration and noise,which have a serious influence on the safety and concealment of the equipment.Based on the theory of phononic crystals,this paper studies the vibration transfer properties of a locally resonant(LR)pipe under the condition of fluid–structure interaction.The band structure and the vibration transfer properties of a finite periodic pipe are obtained by the transfer matrix method.Further,the different impact excitation and fluid–structure interaction effect on the frequency range of vibration attenuation properties of the LR pipe are mainly considered and calculated by the finite element model.The results show that the existence of a low-frequency vibration bandgap in the LR pipe can effectively suppress the vibration propagation under external impact and fluid impact excitation,and the vibration reduction frequency range is near the bandgap under the fluid–structure interaction effect.Finally,the pipe impact experiment was performed to verify the effective attenuation of the LR structure to the impact excitation,and to validate the finite element model.The research results provide a technical reference for the vibration control of the fluid-conveying pipe systems that need to consider blast load and fluid impact.

Locally Asymptotic-norming Property and Kadec Property

In this paper we study the three new asymptotic-norming properties which are called locally asymptotic-norming property k,k=Ⅰ, Ⅱ,Ⅲ, and discuss the relationship between the locally asymptotic-norming property and the Kadec Property.

Asymptotic-norming and Locally Asymptotic-norming Property of Banach Spaces

The relationship between some smoothness and weak asymptotic-norming properties of dual Banach space X is studied. The main results are the following. Suppose that X is weakly sequential complete Banach space, then X is Frechet differentiable if and only if X has B （X）- ANP -I, X is quasi-Frechet differentiable if and only if X has B（X）- ANP -H and X is very smooth if and only if X has B（X）- ANP -Ⅱ. A new local asymptotic-norming property is also introduced, and the relationship among this one and other local asymptotic-norming properties and some topological properties is discussed. In addition, this paper gives a negative answer to the open question raised by Hu and Lin in Bull. Austral. Math. Soc,45,1992.

Approach for Obtaining Material Mechanical Properties in Local Region of Structure Based on Accurate Analysis of Micro-indentation Test

The hot or cold processing would induce the change and the inhomogeneous of the material mechanical properties in the local processing region of the structure,and it is difficult to obtain the specific mechanical properties in these regions by using the traditional material tensile test.To accurately get actual material mechanical properties in the local region of structure,a micro-indentation test system incorporated by an electronic universal material test device has been established.An indenter displacement sensor and a group of special micro-indenter assemblies are estab-lished.A numerical indentation inversion analysis method by using ABAQUS software is also proposed in this study.Based on the above test system and analysis platform,an approach to obtaining material mechanical properties in the local region of structures is proposed and established.The ball indentation test is performed and combined with the energy method by using various changed mechanical properties of 316L austenitic stainless steel under differ-ent elongations.The investigated results indicate that the material mechanical properties and the micro-indentation morphological changes have evidently relevance.Compared with the tensile test results,the deviations of material mechanical parameters,such as hardness H,the hardening exponent n,the yield strength σy and others are within 5%obtained through the indentation test and the finite element analysis.It provides an effective and convenient method for obtaining the actual material mechanical properties in the local processing region of the structure.

Regulating Electron-Hole Separation to Promote the Photocatalytic Property of BiOBr_1−xI_x/BiOBr Local Distorted Hierarchical Microspheres

In this work, hierarchical BiOBr1−xIx/BiOBr heterojunction photocatalyst with a microsphere morphology was synthesized by a facile solvothermal process. It demonstrated that the local structure of the photocatalysts was highly distorted due to the substitution of bromide ions by iodine ions. The photocatalytic properties were evaluated by the photodecomposition of aqueous phenol solution under visible-light irradiation. The results indicated that all the composite photocatalysts exhibited high photocatalytic activity. In particularly, the BiOBr1−xIx/BiOBr (x = 0.25) sample exhibited over 92% degradation efficiency of phenol within 150 min, which is 24.6 and 3.08 fold enhancement in the photocatalytic activity over the pure phased BiOBr and BiOI, respectively. Moreover, this excellent photocatalytic property can be expanded to other colorless organic contaminants, verifying the common applicability of BiOBr1−xIx/BiOBr (x = 0.25) as an excellent visible-light photocatalyst for organics decomposition. The significant improvement in the photocatalytic activity can be explained by the high efficiency of charge separation due to the enhancement in the internal electric fields and band match that comes from the local structure distortion. This work provides valuable information for the design of highly active photocatalysts toward the environmental remediation.

Property Tax Performance of Local Authorities in Malaysia

Property tax income of local authorities has become more challenging due to robust developments. Property tax revenue is the main income for local authorities that are used to pay for services and maintenance in the local authority administrative areas. However, the amount of revenue collected is decreasing due to the serious problem of property tax arrears that affects the administrative system and as a corollary, the delivery of services by local authorities. The performance measurement of property tax is very important in order to manage the services, and for maintenance and development of sustainable local authorities. Therefore, this paper represents a review of the Malaysian local authority property tax collection performance. The rating system is applied to address the performance of property tax collection in Malaysia. The result revealed that most of the property tax collection in Malaysia performed under inadequate level. Property tax collection statistics for the research include the total revenue and property tax arrears for each local authority in Malaysia within five years from 2004 to 2007. It is expected that this property tax performance will be employed as a basis to pursue the appropriate, innovative, and creative approaches for local authorities in Malaysia.

Comparative Study of the Thermal and Mechanical Properties of Foamed Concrete with Local Materials

Living in a habitat with comfort is requested by all. Cinder block bricks have poor thermal properties, leading people to use fan heaters and air conditioners to regain comfort. To overcome this problem of thermal discomfort in buildings, we used lightweight concrete such as foamed concrete which is a material that has improved thermal properties for thermal comfort. In addition, this material was compared with local materials used for the construction of buildings such as BTC, adobe and BLT mixed with binders. The results showed that foamed concrete is a material that has good thermal and mechanical properties compared to local materials mixed with binders. The foamed concrete having acceptable thermo-mechanical properties was that having a density of 930 kg/m3. It has a thermal resistance of 0.4 m2·K/W for a thickness of 20 cm. The foamed concrete having acceptable thermo-mechanical properties was that having a density of 930 kg/m3. It has a thermal resistance of 0.4 m2·K/W for a thickness of 20 cm. For sunshine on a daily cycle equal to 12 hours, the characteristic thickness achieved by this material is 7.29 cm. It also has a shallow depth of heat diffusion having a lower thickness than other materials. This shows that foamed concrete is a promising material for the construction of buildings.

Characterization of Nano-Silica Local Metakaolin Based-Geopolymer: Microstructure and Mechanical Properties

The current study focused on the utilization of local clay for synthesis and characterization of meta-kaolin based geopolymers with and without nano-silica. The control geopolymers, for a compressive strength of 30 MPa, were optimized by using Liquid/Solid ratio of 0.55, NaOH concentration of 10 M and curing at 80°C. The nano silica was added in an extended range of 1%, 2%, 3%, 5%, 7% and 10%. The synthesized nano-silica metakaolin based geopolymers was investigated by using compressive strength, XRD, XRF, FTIR, SEM, MIP, TG, UV/VIS spectroscopy, in addition to density, water absorption and initial setting times. The results indicated an increase in the compressive strength value with the incorporation of nano-silica in geopolymer mixes until the optimum percentage of 5%, while the 10% addition of nano-silica decreased the compressive strength by 5% as compared to the control geopolymer. The increase in the compressive strength was accredited to the increase in the content of N-A-S-H gel and the amorphous structure as shown by XRD and FTIR analysis. In addition, the optical transmittance analysis, MIP and SEM scans along with the results of density and water absorption have clearly shown the densification of the matrix formed for the optimal percentage of nano-silica. However, the initial setting time was found to reduce substantially with increase of nano-silica content. Moreover, the TG results have shown the 5% nano-added geopolymers to have greater thermal stability as compared to reference geopolymers. Finally, the adopted methodology in this research has shown that 5% nano-silica, is the optimal result for the synthesis and the production of local meta kaolin based geopolymer, with regard to the improvement of physical properties, micro structure and compressive strength.

知识产权是发展新质生产力的第一要素

生产要素、生产力与生产关系三者互动式发展,是人类社会进步的推动力量。从古典政治经济学到马克思主义的生产力理论及其中国当代“新质生产力”的理论创新,推动生产力发展的要素从“点状”到“面状”,已呈“立体状”。在新型生产要素及其组合创新中,知识产权是其内核。发展新质生产力,一方面要注重本土资源开发与知识产权保护,另一方面要将知识产权转化为现实生产力。同时,通过健全知识产权专门化审判体系,强化司法对新技术、新模式、新业态、新领域的促进作用,营造适应新质生产力发展的法律环境。在新质生产力的语境下,知识产权具有要素资源和法权双重属性,是发展新质生产力的第一要素。

制度变迁背景下集体建设用地改造与政府角色回归:以佛山市南海区为例

集体建设用地再开发是盘活存量,促进城市高质量发展的主要途径,伴随着集体土地产权制度路径依赖式的变迁:自上而下的土地确权正式化集体建设用地的存在,赋予村集体权利,但在土地初次开发中自下而上形成的制度制约着改造。文章探讨制度变迁下,地方政府如何与村集体互动,化解上述制度制约,促进集体建设用地市场化改造的。研究发现,集体建设用地正式化开启了改造市场,但仍受空间破碎、集体土地经营内卷化、开发权模糊的约束。地方政府发挥了企业化的非正式角色,与村集体形成合作与竞争并存的协商型合作关系。合作在于政府从供、需两侧化解前述制约,充当村集体与市场主体间的“交易中介”,降低交易成本,助力改造。竞争表现为村集体为攫取地租把持政府,损害社会公平。地方政府的“非正式”角色应予以制度化,以规避其在维护社会公益上的失灵。

考虑双向流固耦合的受泥流冲刷桥墩力学性能分析

基于双向流固耦合理论和湍流理论,建立泥流冲击桥墩数值分析模型,并采用文献试验数据进行了验证。设定了3种不同截面的立柱进行冲刷计算,结果表明圆形截面立柱抗冲刷能力最好,三角形截面立柱导流效果较好。针对圆形截面桥墩进行了4种不同含沙量泥流冲刷工况的数值模拟,结果显示:含沙量越大,立柱被泥流冲刷破坏的可能性越大,与冲击力对比佐证,含沙量越大的泥流对立柱的损伤越强,此外,在一定含沙量范围内,桥墩动力响应会随着泥流含沙量的增大而增大,但超出这一范围,动力响应将骤减。

核电厂定位销局部干法水下TIG焊接工艺

以核电厂定位销水下焊接为研究对象,研制双层气体保护的局部干法水下TIG旋转焊枪,运动轨迹通过直流电机带动钨极绕固定直径转动实现.对核级材料Z2CN19-10控氮奥氏体不锈钢进行焊接,研究局部干法水下TIG焊接焊缝成形,优化工艺参数,结合热循环曲线及电弧形态,分析焊接接头显微组织及力学性能.结果表明,当焊枪的内层和外层保护气均通氩气时,焊缝成形良好,电弧形态稳定;增大焊接电流或减小焊接速度均使焊缝熔深增大,熔宽增大;对比水下焊接接头和陆上焊接接头发现,水的快速冷却作用会促使熔合线附近的铁素体的形态由树枝状转变为板条状,奥氏体含量减少,焊缝中心晶粒细化;水下焊接接头的显微硬度和力学性能略高于陆上焊接接头.

中小型无人机国产碳纤维复合材料剪切性能研究

研究测试了不同国产碳纤维预浸料的剪切性能,包括层间剪切性能和纵横剪切性能。TT700S层间剪切性能是60.3 MPa,ZT7G材料层间性能达到81.8 MPa,CQ材料层间性能达到79.3 MPa,EM118材料层间性能达到64.5 MPa。T700高温碳纤维,层间剪切强度达到97.3 MPa,T800高温碳纤维层间剪切强度达到102 MPa。纵横剪切性能均高于MTM28进口材料。结果表明,目前国产碳纤维预浸料力学性能基本与进口材料相当,能够应用中小型无人机的设计和生产。