离子注N对6061铝合金表层晶粒取向的影响

通过掠入射X射线衍射及面探扫描实验研究了经氮离子注入后,6061铝合金表层的晶粒取向。结果表明离子注入对铝合金表层的晶粒取向有较大影响,并且随着注入时间的增加,其晶粒取向也发生变化。同时对离子注入层中晶粒取向的形成进行了探讨。     

Effect on the grain interior and grain boundary reactions by Cr addition to low gold content alloys

The effect on grain interior and grain boundary reactions by Cr addition to low gold content alloys were investigated by electric resistivity measurements, hardness tests, optical microscopic observations, and TEM observations. The grain interior reactions were accelerated by the chromium addition while grain boundary reactions were retarded. The formation of AuCu l type ordered phase in the grain interior was accelerated, and the T-T-T curve of AuCu l type ordered phase shifted to higher temperatures and shorter times with increasing chromium content.     

Effect of grain orientation on aluminum relocation at incipient melt conditions

Aluminum is commonly used for structural applications in the aerospace industry because of its high strength in relation to its weight. It is necessary to understand the mechanical response of aluminum structures at elevated temperatures such as those experienced in a fire. Aluminum alloys exhibit many complicated behaviors that require further research and understanding, such as aluminum combustion, oxide skin formation and creep behavior. This paper discusses the effect of grain orientation on aluminum deformation subjected to heating at incipient melt conditions. Experiments were conducted by applying a vertical compressive force to aluminum alloy 7075 block test specimens. Compression testing was done on test specimens with the applied load on the long transverse and short transverse orientations. Results showed that the grain orientation significantly influences aluminum’s strength and mode of failure.     

Failure of AA 6061 and 2099 aluminum alloys under dynamic shock loading

Microstructural aspects of the deformation and failure of AA 6061 and AA 2099 aluminum alloys under dynamic impact loading are investigated and compared with their responses to quasi-static mechanical loading in compression. Cylindrical specimens of the alloys, heat-treated to T4, T6 and T8 tempers, were subjected to dynamic compressive loading at strain rates of between 2800 and 9200 s⁻¹ and quasi-static compressive loading at a strain rate of 0.0032 s⁻¹. Plastic deformation under the dynamic impact loading is dominated by thermal softening leading to formation of adiabatic shear bands. Both deformed and transformed shear bands were observed in the two alloys. The shear bands offer preferential crack initiation site and crack propagation path in the alloys during impact loading leading to ductile shear fracture. While cracks propagate along the central region of transformed bands in AA 6061 alloy, the AA 2099 alloy failed by cracks that propagate preferentially along the boundary region between the transformed shear bands and the bulk material. Whereas the AA 2099 alloy shows the greatest propensity for adiabatic shear banding and failure in the T8 temper condition, AA 6061 alloy is most susceptible to formation of adiabatic shear bands and failure in the T4 temper. Deformation under quasi-static loading is dominated by strain hardening in the two alloys. Rate of strain hardening is higher for naturally aged AA 6061 than the artificially aged alloy, while the strain hardening rate for the AA 2099 alloy is independent of the temper condition. The AA 2099 alloy shows a superior mechanical behaviour under quasi-static compressive loading whereas the AA 6061 shows a higher resistance to impact damage.     

Fracture of laminates combining 2024-T3 and 7075-T6 aluminum alloys

Crack growth resistance curves have been determined for crack-divider laminates in which layers of 2024-T3 aluminum alloy are adhesively bonded to layers of 7075-T6 alloy. Results are compared with the fracture resistance of laminates consisting wholly of each material, the layer thickness being the same (1.54 mm) in all cases. The initial portions of the resistance curves are similar for both alloys; however those for 2024-T3 have steeper slopes at longer effective crack lengths. As a result, laminates consisting entirely of 2024-T3 alloy exhibit greater amounts of stable crack extension and higher toughnesses at instability. This is attributed in part to the greater strain hardening rate in 2024-T3 material. Laminates combining 2024-T3 and 7075-T6 layers are intermediate between those consisting entirely of one or the other alloy.     

压力及制备条件对大块非晶合金结构的影响

大块非晶合金又称大块金属玻璃,是一种具有特殊结构与性能的新型金属材料.本文利用同步辐射XRD技术研究了常压和11.6GPa压力下Zr41.2Ti13.8Cu12.5Ni10Be22.5大块非晶合金结构以及0～50GPa压力范围内Fe60Co10Zr8Mo5Nb2B15大块非晶形成合金结构特征的演变.另外,利用同步辐射XRD研究了冲击波处理和水淬条件下制备的Zr41.2Ti13.8Cu12.5Ni10Be22.5大块非晶合金微观原子构型的差异.研究表明,压力与制备条件对大块非晶合金的结构均有一定影响,本研究对深入了解大块非晶合金结构本质及进一步开发该类材料具有重要理论和现实意义.     

Environmental effects on low cycle fatigue of 2024-T351 and 7075-T651 aluminum alloys

The environmental effects on the low cycle fatigue (LCF) behavior of 2024-T351 and 7075-T651 aluminum alloys were studied at room temperature. The specimens were subjected to identical LCF tests at strain ratio R of −1 and frequency of 5 Hz in three environments: vacuum, air and 1% NaCl solution of pH 2. A separate group of specimens was pre-corroded in 1% NaCl solution and then LCF-tested in air. Their strain–life relations and cyclic stress–strain responses were investigated and compared. Furthermore, the fracture surface morphology was evaluated to find the association of LCF behavior and fractographic features under different environmental conditions.     

Friction stir welding of dissimilar materials between AA6061 and AA7075 Al alloys effects of process parameters

Dissimilar AA6061 and AA7075 alloy have been friction stir welded with a variety of different process parameters. In particular, the effects of materials position and welding speed on the material flow, microstructure, microhardness distribution and tensile property of the joints were investigated. It was revealed that the material mixing is much more effective when AA6061 alloy was located on the advancing side and multiple vortexes centers formed vertically in the nugget. Three distinct zones with different extents of materials intercalations were identified and the formation mechanism of the three zones was then discussed. Grain refinement was observed in all three layers across the nugget zone with smaller grains in AA7075 Al layers. All the obtained joints fractured in the heat-affected zone on the AA6061 Al side during tensile testing, which corresponds very well to the minimum values in microhardness profiles. It was found that the tensile strength of the dissimilar joints increases with decreasing heat input. The highest joint strength was obtained when welding was conducted with highest welding speed and AA6061 Al plates were fixed on the advancing side. To facilitate the interpretation, the temperature history profiles in the HAZ and at zones close to TMAZ were also measured using thermocouple and simulated using a three-dimensional computational model.     

Microstructure and mechanical properties of dissimilar friction stir welding of 6061-to-7050 aluminum alloys

In this work, the microstructure and mechanical properties of friction stir welded dissimilar butt joints of 6061-to-7050 aluminum alloys were evaluated. Microstructure analysis of the cross-section of the joints revealed distinct lamellar bands and various degrees of intermixing that were correlated with tool rotational speed. Due to the distinct mechanical properties of the two alloys, microhardness measurements showed a consistent asymmetric hardness distribution profile across the weld nugget, regardless of tool rotational speed. Under monotonic tensile loading, an increase in the joint strength was observed with the increase in the tool rotational speed. Regarding fracture, the joints consistently failed on the 6061 aluminum alloy side. Furthermore, two modes of failure were observed, one through the stir zone and the other through the heat-affected zone. Inspection of the fracture surfaces suggested that inadequate material intermixing produced at low tool rotational speeds was the cause for the low mechanical strength and failure through the stir zone. On the other hand, the failure observed through the heat-affected zone at high rotational speeds was produced due to the material softening as confirmed by the microhardness measurements.     

微量元素Cr、Zr对铜合金性能的影响

分析了纯铜及合金Cu-Cr、Cu-Zr、Cu-Cr-Zr的力学性能、导电性能和耐蚀性能,研究了微量元素Cr、Zr的添加对纯铜性能的影响。结果表明,微量元素Cr、Zr的添加可显著提高纯铜的强度,强化方式为析出强化;时效过程中析出的弥散相从一定程度上阻碍了电子的运动,使合金的导电性能降低;在中性盐雾环境中,纯铜及合金的失重速度随时间延长呈上升趋势,微量Cr的添加可以提高纯铜的耐蚀性能,而微量Zr的添加则使纯铜的耐蚀性有降低的趋势。     

Intergranular corrosion behavior of the 7075-T6 aluminum alloy under different annealing conditions

The effect of annealing conditions producing various grain sizes on the intergranular corrosion behavior of high-strength aluminum alloy type 7075-T6 was investigated using electrochemical polarization techniques. Aluminum alloy specimens with large grain size exhibited lower breakdown potentials in deaerated 0.5 M NaCl solution. The breakdown potentials decreased with increasing grain size. Microscopic observations of the exposed surfaces during potentiostatic polarization testing showed that the coarse grain structure promotes intergranular crack growth.     

Effect of orientation on self-organization of shear bands in 7075 aluminum alloy

The spatial distribution of shear bands was investigated in the rolled 7075 aluminum alloy through the thick-walled cylinder (TWC) technique with 0°, 90° and 45° angles between the aluminum alloy cylinder axial direction and the rolling direction. Self-organization of multiple adiabatic shear bands was observed in different orientation specimens and investigated by using Schmid factor theories. The experimental results indicated obvious differences in the morphology and self-organization of shear bands for the specimens. At the initial stage, the spacing of the shear bands in the 0° specimen is smaller than in the other specimens. The nucleation of the shear bands in the 90° specimen is early. Due to the shielding effect, fast-developed shear bands block the development of the neighboring smaller shear bands in the 90° specimen. The spacing of the shear bands in the 45° specimen is much larger than in the other specimens under the similar effective strain. At the late stage, a large number of shear bands nucleate in the 0° specimen, and the spacing of the shear bands is small. The shear bands in the 90° specimen are well-developed with obvious shielding effect and the largest spacing. The 45° specimen has the maximum average nucleation rate of the shear bands. Owing to the close Schmid factors of the slip systems of the 45° specimen, the spacing of the shear bands in the 45° specimen is still larger than in the 0° specimen.