Effect of wire brushing on warm roll bonding of 6XXX/5XXX/6XXX aluminum alloy clad sheets

Three-layered 6XXX/5XXX/6XXX aluminum alloy clad sheets were fabricated by warm roll bonding and the effect of wire brushing on the threshold reduction and bonding strength was studied. When the sheets were wire-brushed before rolling, the threshold reduction for successful bonding was reduced, and bonding strengths were lower than those of the non-brushed sheets. The difference between the threshold reduction of the brushed and non-brushed sheets decreased with increasing rolling temperature. The bonding strength of the non-brushed sheets was higher than that of the brushed sheets because the bonding area was larger. In the non-brushed sheets, deformation between the clad and the core may be responsible for waviness and crack formation, causing interfacial sliding at the bonding interface, enlarging the bonding area, and increasing the bonding strength.     

走进张志刚的工作室

张志刚的网名叫“温柔牦牛”，在云南，张志刚则有摄影师和导演两种身份。令很多人难以置信的是：他驾驶着一辆微型面包车，几次游走在滇藏线上。甚至有连车带人翻滚到河谷中生还的经历，颇令人替他担心，但就是这辆微面。载着他拍摄了大量照片和高清影像资料。回到昆明的工作室。他又开始着手剪辑高清纪录片，准备着电台的讲座，盘算着下次再从哪条路进藏……[编者按]     

Fabrication Conditions, Microstructures and Mechanical Properties of P/M Processed 2XXX Al-SiCW Composites

The powder metallurgy fabrication of 2XXX Al composites reinforced with SiC whiskers was studied by investigating the evolution of microstructure and its relation to the mechanical properties. In this study, SiC whiskers and gas-atomized aluminum powders were mixed by fluid zone mixer, consolidated by vacuum hot press, and then extruded. The optimum condition for consolidation was 620°C and 50 MPa, at which fully densified pore-free billets were obtained. The composites with relatively homogeneous microstructures were produced by extrusion at 450–500°C under the extrusion pressure of 700–1000 MPa. The mechanical properties of the extruded bars were found to be comparable with those of the composites processed by Advanced Composite Materials Corp. The optimum fabrication conditions have been proposed for producing composites of improved mechanical properties through elimination of coarse intermetallic particles, uniform distribution of reinforcements, and minimization of whisker breakage. The possibility of using particulates rather than whiskers, and the modification of the alloy matrices for high temperature applications are also discussed in relation to the distribution of reinforcements and the optimization of the consolidation temperature.     

Fatigue behavior of SiC particulate reinforced spray-formed 7XXX series Al-alloys

This paper presents the fatigue results obtained in high strength spray-formed 7XXX series Al-alloys reinforced with the addition of silicon carbide particulate. This is one in a series of papers reporting on experimental studies completed to analyze the effects of processing and composition on numerous properties of these 7XXX series Al-alloys. In this study, testing was performed in tension on specimens with a constant amplitude axial fatigue cycle of R = ?1.0. Test results were also compared with results available in the literature. The metal matrix composite materials displayed a large increase in fatigue strength in comparison to commercial ingot metallurgy 7075-T6 and T7 alloys. The enhanced fatigue performance of the spray formed alloys is attributed to low crack growth rates, resulting from inhomogeneous slip.     

喷丸强化对2XXX铝合金疲劳寿命的影响

研究喷丸对2XXX铝合金拉-拉疲劳性能的影响。对未喷丸试样和喷丸强化试样的微观组织、显微硬度、残余应力和拉-拉疲劳性能进行对比分析。结果表明:喷丸处理后,试样的组织和微结构未发现明显变化,但其粗糙度、残余压应力和显微硬度有所提高,分别是未喷丸试样的6.25倍,3.85倍和1.12倍;拉-拉疲劳性能显著提高,其中值疲劳寿命是未喷丸的1.67倍。在99.9%存活率下,喷丸试样的安全寿命是未喷丸试样的1.45倍。且表面喷丸强化后疲劳裂纹源由多个变为一个。     

Influence of corrosion and creep on intergranular fatigue crack path in 2XXX aluminium alloys

In this paper, two examples of the influence of time-dependent processes on crack path in two 2XXX aluminium alloys are presented. The first example is concerned with corrosion-fatigue crack growth resistance of a 2024 T351 alloy cracked in the S-L direction in 3.5% NaCl solution at free corrosion potential. The second example deals with the elevated temperature crack growth resistance of a 2650 T6 alloy that might be used in future supersonic aircraft fuselage panels. The common idea is to correlate quantitative measurements of relevant fractographic features of crack path to the effects of time-dependent processes on crack growth rates.     

Quantification of grain boundary precipitation and the influence of quench rate in 6XXX aluminum alloys

The extent of grain boundary precipitation has a strong influence on the ductility, fracture toughness and formability of Al alloys. An experimental method for quantifying the level of grain boundary precipitation is described and applied to the Al alloy AA6111 subjected to a range of quenching rates. A threshold quenching rate can be identified above which the degree of grain boundary precipitate is insensitive to the quenching rate.     

高强韧低淬火敏感性7XXX系铝合金的发展

高强韧低淬火敏感性7XXX系铝合金,是满足航空工业当前及未来发展对厚截面整体式结构件制造紧迫需求的必然选择,是当前世界各国在航空铝合金材料研发方面的热点和重点。近年来,美欧等发达国家开创了以7085合金为代表的新一代高强韧低淬火敏感性7XXX铝合金材料体系;我国也成功开发出了一种具有完全自主知识产权、综合性能优异的高强韧低淬火敏感性铝合金材料。详细介绍了国内外高强韧低淬火敏感性7XXX系铝合金的特征、发展历史和现状,并总结了其未来发展方向。在厚截面铝合金材料的设计和生产过程中,通过成分优化设计和组织控制以最大可能地降低合金的淬火敏感性,是发展新一代高强韧低淬火敏感性铝合金材料的必由之路。     

AN EVALUATION OF FATIGUE AND FRACTURE MECHANICS PROPERTIES OF ULTRA-HIGH STRENGTH 7XXX SERIES Al-ALLOYS

Abstract— The fatigue and fracture mechanics properties of rapidly solidified ultra-high strength 7XXX series Al-alloys have been studied. With respect to conventional high-strength Al-alloys, these materials exhibited a better fatigue-endurance on both plain and notched specimens at low stress amplitude in constant amplitude fatigue tests, whereas the opposite occurred at high stress amplitudes. Fatigue crack growth tests indicated lower crack growth rates at low Δ K -levels, but at intermediate and high Δ K -values these materials were particularly prone to additional components of "static" crack propagation, which led to steeply inclined d a/ d N vs Δ K curves. Moreover, the increase in tensile strength was linked with some loss of ductility and fracture toughness. Overload regions were characterized by a large amount of intergranular decohesion, possibly facilitated by the presence of incoherent particles at grain boundary regions and by the large strength differential between the matrix and precipitate free zone. The best results in terms of elongation to rupture and toughness were obtained by reducing the amount of Cr/Mn incoherent dispersoid-forming elements, in order to lessen the tendency towards matrix-dispersoid interface decohesion at grain boundaries.     

Preparation and Properties of Sodium, Potassium, Magnesium, Calcium, and Aluminum Terephthalates

Group I–III terephthalates were prepared: KOOCC₆H₄COOH, NaOOCC₆H₄COOH, NaOOCC₆H₄COONa, Mg(OOCC₆H₄COO) · 2H₂O, Ca(OOCC₆H₄COO) · 3H₂O, and Al₂(OOCC₆H₄COO)₃ · 8H₂O. The salts were characterized by differential thermal analysis and IR spectroscopy. The results demonstrate that the thermal decomposition of the terephthalates yields metal carbonates or oxides. On heating to 1000°C, aluminum terephthalate converts into submicron-sized -alumina particles.     

Structural transformations, reactions, and electronic properties of fullerenes, onions, and buckytubes

We describe the results of extensive quantum molecular dynamics calculations of the properties of fullerenes and microtubules. The topics to be discussed include: (i) stability of C₆₀ isomers and barriers to isomerization; (ii) reactivity of C₆₀ and C₅₈ with C₂ and C₃, and its implications on the formation and growth of fullerenes; and (iii) atomic and electronic structure and doping of semiconducting microtubules. We also discuss the structures, stabilities and atomic transformations of large multishell fullerenes and offer an explanation for the formation of spheroidal “onions” under high fluence electron irradiation conditions. The last results, which involved calculations for up to 15 000 atoms, were obtained using classical three-body potentials.     

Synthesis and structure of dodecamolybdates of tetravalent cerium,thorium, uranium,neptunium, and plutonium

A series of isostructural compounds of the composition Na₇H[EMo₁₂O₄₂]·12H₂O, where E(IV) = Ce, Th, U, Np, or Pu, were synthesized and structurally characterized. In the [EMo₁₂O₄₂]^8– heteropolyanion (HPA), the central E(IV) atom is surrounded by six Mo₂O₉ groups, each constituted by two octahedra sharing a common face. The coordination polyhedron (CP) of the central atom is a weakly distorted icosahedron with the mean E(IV)–О bond lengths of 2.498, 2.529, 2.500, 2.490, and 2.488 Å for Ce, Th, U, Np, and Pu, respectively. In the structure of the compounds Na₇H[EMo₁₂O₄₂]·12H₂O, there are two crystallographically independent sodium atoms: Na(1) and Na(2). The oxygen surrounding of the Na(1) atom is formed by the terminal oxygen atoms of two heteropolyanions adjacent along [001], and its coordination polyhedron is an octahedron. The surrounding of the Na(2) atom (a six-vertex polyhedron) is formed by three terminal oxygen atoms of three Mo₂O₉ groups belonging to the same HPA and by three water molecules. The coordination polyhedra of the Na(2) atoms are linked with each other via common oxygen atoms of O_w(2) water molecules to form a chain “winding” around the 3₁ screw axis. The heteropolyanions and Na⁺ cations in the crystal form a framework constructed in a fashion characteristic of Dexter–Silverton type anions, with the coordination via three terminal oxygen atoms of three Mo₂O₉ groups. Excess negative charge of HPA is compensated by the proton localized on one of the six bridging O atoms. In the Mo₂O₉ doubled octahedra, the Mo–O bonds with the О atoms bonded to E(IV) and forming the edge of the common face are sensitive to the kind of the central atom.     

Elastic, structural, bonding, and defect properties of zinc-blende BN, AlN, GaN, InN and their alloys

Simple tight-binding simulations, incorporating only the Herman–Skillman atomic term values, are shown to provide valuable information about the bonding, elastic and structural properties of zinc-blende group III-nitrides. Our calculated values of the elastic parameters (viz., bulk modulus, elastic stiffness constants, Kleinman's internal displacement parameter, Keating force constants, etc.) for BN, AlN, GaN, and InN are shown to exist well within the range of values derived from more sophisticated methods. Despite the crude approximations used, the tight-binding method has clearly provided the meaningful trends to the local distortions around isoelectronic impurities and has described reasonably well the bond length variations as a function of composition in ternary alloys.     

Autonomy, security, and inequality: China, India, the United States, and the globalization of science and technology

Perhaps no three countries have benefited from the globalization of science and technology (S&T) more than India, China, and the United States. All three have leveraged the growing internationalization of innovation to offset weaknesses in their own national innovation systems. Still, globalization raises critical questions of autonomy, security, and equality, and in turn the political struggle over these three issues shapes the pace and scope of the globalization of S&T. Significant deterioration on any one of these criterion could lead to substantially less support among policy makers and the public for the globally networked system of innovation that appears to be emerging.     

Modeling the release, spreading, and burning of LNG, LPG, and gasoline on water

Current interest in the shipment of liquefied natural gas (LNG) has renewed the debate about the safety of shipping large volumes of flammable fuels. The size of a spreading pool following a release of LNG from an LNG tank ship has been the subject of numerous papers and studies dating back to the mid-1970s. Several papers have presented idealized views of how the LNG would be released and spread across a quiescent water surface. There is a considerable amount of publicly available material describing these idealized releases, but little discussion of how other flammable fuels would behave if released from similar sized ships. The purpose of this paper is to determine whether the models currently available from the United States Federal Energy Regulatory Commission (FERC) can be used to simulate the release, spreading, vaporization, and pool fire impacts for materials other than LNG, and if so, identify which material-specific parameters are required.

The review of the basic equations and principles in FERC's LNG release, spreading, and burning models did not reveal a critical fault that would prevent their use in evaluating the consequences of other flammable fluid releases. With the correct physical data, the models can be used with the same level of confidence for materials such as LPG and gasoline as they are for LNG.