Functional and Functionally Structured Materials II

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Authors: Yu Wan Cheng, Zhi Yu Xiao, Hai Ping Zou
Abstract: Gas atomization is one of the most cost-effective methods for preparing spherical powders. The Cu-9.7Sn-0.2P alloy powder for 3D printing was prepared by a self-developed double nozzle gas atomization technique with different deliver tube diameters, and the particle size and shape of the powder were characterized. Results show that the powder particles are mostly nearly spherical, mixed with a few irregular powders. The average O. Bluntness of the powders are 60~70%, the average Outgrowths are lower than 18%. The deliver tube diameter affects the powder characteristics directly. The increase of the diameter increases the particle size of the powder and reduces the sphericity. At the same time, the adhesion of the satellite powder decreases, the flowability becomes better and the oxygen content drop. The surface and internal structure of the powder are mainly cellular and dendritic structures.
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Authors: Zhen Shan Liu, Pi Zhi Zhao, Jing Wei Zhao
Abstract: With the development of light-weighting vehicles, AA5754 sheets are widely utilized as automotive structure material. Its strength and formability are greatly related to the recrystallization process. The recrystallization behavior of AA5754 sheets at high temperature in short time (in minutes) was rarely reported. In present work AA5754 sheets with cold rolling reduction from 58 to 75% was annealed in short time (max 6 min) at 310 and 320°C. Its recrystallization behavior was studied by means of microstructure observation and tensile testing. Microstructure shows that the incubation time varies in the range of 30-120 seconds with cold rolling reduction. The incubation time becomes shorter with the higher cold rolling reduction. According to the tensile strength, the recrystallization kinetics was expressed with JMAK equation. The JMAK equation fitted with recrystallization time gives a better agreement with experimental results than that fitted with annealing time. The calculated apparent activation energy for recrystallization decreases with the increasing cold rolling reduction, indicating that the recrystallization occurred much easier in AA5754 sheet with higher cold rolling reduction.
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Authors: Ming Tu Ma, Jun Ping Zhang, Jia Zhou, Hong Zhou Lu
Abstract: Based on the requirements of automotive closure for production process and service performance, the property requirements of aluminum alloy sheet for automotive closure, including aging resistance stability, formability, bake hardening, dent resistance, flanging ductility, painting compatibility, etc., as well as introduced their test methods, evaluation characterization parameters, and the pre-aging process were discussed in this paper. Specially, the influential factors and control methods of spring-back of aluminum alloy sheet was discussed. The effect of the pre-aging process on the aging resistance stability and bake hardening of the aluminum alloy sheet for automotive was analyzed, and the property evolution of aluminum alloy sheet under industrial pre-aging process studied. The orange peel and roping phenomena of Al-Mg-Si alloy sheet after deformation were summarized as well.
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Authors: Ran Liu, Hui Huang, Ya Liu, Li Rong
Abstract: To study the hot deformation behavior of Al-Mg-Er alloy, hot compression tests were conducted on a Gleeble-1500D thermal simulator at the temperature range of 200-500°C with the strain rates from 0.001 to 10s-1. With the increase in the deformation temperature and the decrease in strain rates, the flow stress of the Al-Mg-Er alloy decreased. Processing maps were constructed to study on hot workability characteristics. The results showed that the flow stress curves exhibited the typical dynamic recrystallization characteristics and the stress decreased with the increase of deformation temperature and the decrease of strain rate. Moreover, the processing maps were established on the basis of dynamic material model and Prasad’s instability criterion.
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Authors: Yang Yang, Pi Zhi Zhao, Li Ying Zou, Rong Hui Fan
Abstract: By means of Vickers hardness tester, optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD) and high resolution transmitted electron microscope (HRTEM), the bake softening and precipitation behaviors of AA5182 H19 sheet for can end stock at 205°C and 249°C were investigated. All specimens at both temperatures showed recovery and bake softening phenomenon, which meaning the dislocation density and HV decreased. However, the specimens baked at 205°C showed higher recovery impediment, because the bake softening curve departed from the dynamic laws when it had less amount of recovery than the specimens baked at 249°C. The hardness was higher for the specimen baked at 205°C compared with the specimen baked at 249°C, even both specimens had the same dislocation density measured by XRD. Further observations revealed that the precipitated particles in the specimens baked at 205°C distributed along the shear bands. The precipitates were needle shape with the length of 5-15 nm and the width of 5-10 atom layers, which occurred mostly in the area with higher dislocation density. These precipitates were guessed to be Al-Mg binary phases, which could contribute to the higher hardness of the specimens baked at 205°C.
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Authors: Jian Liang He, Da Tong Zhang, Wen Zhang, Cheng Qiu
Abstract: Hot compression tests of as-homogenized Al-7.5Zn-1.5Mg-0.2Cu-0.2Zr alloy were carried out on Gleeble-3500 thermal simulation machine at the temperature ranging from 350°C to 550°C and strain rate ranging from 0.001s-1 to 10s-1. Processing maps were established on the basis of dynamic material model, and the microstructure was studied using electron back scattered diffraction (EBSD) technique. The results showed that the peak stress and steady flow stress decrease with decreasing strain rate or increasing deformation temperature. There are one peak efficiency domain and one flow instability domain in the processing maps. The flow instability domain which exists in high-strain-rate region becomes larger with increasing strain. Shear bands occur at 45° toward the compression axis at grain interiors and meanwhile flow localization occurs. The optimum deformation temperature and strain rate ranges from 450°C to 500°C and 0.003s-1 to 0.1s-1, respectively, with high power dissipation efficiency of 34-39%.
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Authors: Jian Xin Wu, Chong Gao, Rui Yin Huang, Zhen Shan Liu, Pi Zhi Zhao
Abstract: 5083 aluminum alloy, due to moderate strength, good thermal conductivity and formability, is an ideal structural material for car production. Influence of cold rolling process on microstructures and mechanical properties of 5083 aluminum alloys is significant and research hotspots. In this paper, cold deformation and annealing processes on grains, tensile properties and anisotropies of 5083 alloy sheets were studied. Results showed that incomplete recrystallization occured on 5083 alloy sheets when annealing temperature was at 300°C. The degree of recrystallization increased slightly with the cold deformation raised from 30% to 50% and varied slightly with prolonged annealing time from 2h to 4h. Furthermore, fully recrystallization occurred on 5083 alloy sheets at the annealing temperature above 320°C. Tensile strength of 5083 alloy sheets reduced significantly when the annealing temperature was raised from 300°C to 320°C, while it varied slightly when the annealing temperature continued to rise to 380°C.
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Authors: Jun Zhen Gao, Qiang Zhu, Da Quan Li, Yong Lin Kang
Abstract: Turbocharger compressor wheels are often made of 3XX cast aluminum alloys and forged 2618 alloy. These age hardening aluminum alloys have high strength-to-weight ratio at ambient temperature. However, the strength of the aluminum alloys decreases rapidly when applied at high temperatures, such as for turbochargers where application temperature can be above 200 °C. The major reason is that the fine precipitated phases coarsen rapidly tending to their equilibrium states. The thermal stability of the 319s-T61, A201-T71 and 2618-T6 alloys were compared in this paper. The three alloys were exposed at 200 °C for 100 h during heat treatment. Hardness, tensile tests and TEM were carried out to investigate the mechanical properties and microstructure variation of these three alloys. The results indicated that the A201 alloy exhibited the best thermal stability among the three alloys and 319s alloy is the weakest one. TEM observation showed that with the increase of the exposure time, the strengthening precipitates phase θ′ in A201/319s alloys and S′ in 2618 alloy coarsened and then transformed to stable θ phase and S phase, respectively, while the primary strengthening phase Ω in A201 remained stable, which may be contributed the higher thermal stability of A201 than 319s and 2618.
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Authors: Zhu Hua Yu, Da Tong Zhang, Wen Zhang, Cheng Qiu
Abstract: Hot compression tests of homogenized 6063 Al alloy were carried out in the temperatures range from 390°C to 510°C and strain rates from 1s-1 to 20s-1 on a Gleeble-3500 thermal simulation machine. The results showed that the flow stress decreased with increasing deformation temperature or decreasing strain rate. The dynamic softening effect was more obvious when the alloy was deformed at strain rate of 20 s-1. The Arrhenius-type constitutive equation with strain compensation can accurately describe the flow stress of 6063 aluminum alloy during hot compression. Shear bands appeared in grains interior when the alloy deformed at high strain rates, corresponding to high Zenner-Hollomon (Z) parameters. When deformed under the conditions with low Z parameters, the dynamic recrystallization started occurred.
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