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        Measurement and Theoretical Calculation Confirm the Improvement of T7651 Aging State Influenced Precipitation Characteristics on Fatigue Crack Propagation Resistance in an Al–Zn–Mg–Cu Alloy

        Kai Wen,Baiqing Xiong,Yongan Zhang,Zhihui Li,Xiwu Li,Lizhen Yan,Hongwei Yan,Hongwei Liu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5

        Precipitation characteristics influencing fatigue crack propagation contained matrix precipitate, grain boundary precipitateand precipitate free zone for Al–Zn–Mg–Cu alloys. Over-aging treatment could effectively regulate precipitation and then tobe able to change fatigue crack propagation behavior compared with the peak aging state. In the current work, typical T651and T7651 aging tempers of the alloy were extracted via hardness, electrical conductivity and mechanical properties underone-step and two-step aging treatments. Fatigue crack propagation (FCP) rate under them was tested and correspondingprecipitation characteristics and fracture morphology were observed. The results indicated that fatigue crack propagationresistance for the T7651 temper possessed an obvious improvement on the side of that for the T651 temper, which was alsosupported by fracture appearance, including tearing ridge, tearing dimple and fatigue striation. The precipitation observationshowed that the T651 alloy contained GPI zone, GPII zone and ηʹ phase while the T7651 alloy possessed ηʹ phase and η phase.Compared with the T651 temper, matrix precipitate for the T7651 temper distinctly owed an expanding of size distributionand an enlargement of average size while cuttable phase still remained the dominance for both tempers. Grain boundaryprecipitate and precipitate free zone manifested no obvious difference between the two aging tempers. Cut and bypass mechanismsof dislocation–precipitate interactions were used for explanation and it revealed the reinforced cuttable phase was infavor of enhancing fatigue crack propagation resistance. A theoretical model which directly correlated FCP rate with matrixprecipitate characteristics was employed to calculate FCP rate by substituting quantitative precipitate characteristics and thecalculation results were vaguely consistent with the experimental measurement, which proved its reliability and feasibility.

      • KCI등재

        Effect of Various Retrogression Regimes on Aging Behavior and Precipitates Characterization of a High Zn-Containing Al–Zn–Mg–Cu Alloy

        Kai Wen,Baiqing Xiong,Yongan Zhang,Zhihui Li,Xiwu Li,Shuhui Huang,Lizhen Yan,Hongwei Yan,Hongwei Liu 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.3

        In the present work, the infl uence of various retrogression treatments on hardness, electrical conductivity and mechanicalproperties of a high Zn-containing Al–Zn–Mg–Cu alloy is investigated and several retrogression regimes subjected to a samestrength level are proposed. The precipitates are qualitatively investigated by means of transmission electron microscopy(TEM) and high-resolution transmission electron microscopy techniques. Based on the matrix precipitate observations, thedistributions of precipitate size and nearest inter-precipitate distance are extracted from bright-fi eld TEM images projectedalong ⟨110⟩ Al orientation with the aid of an imaging analysis and an arithmetic method. The results show that GP zonesand η′ precipitates are the major precipitates and the precipitate size and its distribution range continuously enlarge with theretrogression regime expands to an extent of high temperature. The nearest inter-precipitate distance ranges obtained arequite the same and the average distance of nearest inter-precipitates show a slight increase. The infl uence of precipitates onmechanical properties is discussed through the interaction relationship between precipitates and dislocations.

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        Facile Fabrication of Extremely Small CoNi/C Core/Shell Nanoparticles for Efficient Microwave Absorber

        Xiang Wen,Lizhen Hou,Lianwen Deng,Daitao Kuang,Heng Luo,Shiliang Wang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.7

        CoNi magnetic nanoparticles (NPs) and hybrid architectures have attracted tremendous attention from numerous applications. In this study, a facile approach based on one-step metal-organic chemical vapor deposition (MOCVD) was developed to fabricate CoNi/C core/shell NPs with an extremely small core size of ~3.7 nm and an ultrathin shell thickness of 1–3 nm. Only 10 wt.% CoNi/C core/shell NP-filled composites with thickness of 1.6 mm exhibit an optimal reflection loss value of -25.7 dB and an absorbing bandwidth value up to 6.2 GHz. The extremely small core/shell NPs are demonstrated to have enhanced electromagnetic parameters (i.e., complex permittivity and permeability), reflection loss and broadened effective absorption bandwidth, as compared to the relatively larger NPs. The superior microwave absorbing performance should be attributed to the increased specific area with enriched interfacial polarization. The as-synthesized extremely small CoNi/C core/shell NPs are expected to be a fascinating candidate for efficient microwave absorption material with lightweight and thin thickness.

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        Maillard Reaction Products of Stir Fried Hordei Fructus Germinatus Are Important for Its Efficacy in Treating Functional Dyspepsia

        Lu Wu,Yan Lai,Ying Wang,Lixia Tan,Lizhen Wen,Huasheng Yang 한국식품영양과학회 2020 Journal of medicinal food Vol.23 No.4

        Hordei Fructus Germinatus (HFG) has been used as a traditional medicine to treat functional dyspepsia (FD) in China. Stir fried HFG (F-HFG) containing Maillard reaction products (MRPs) is used more widely than the raw HFG (R-HFG). However, the exact mechanisms in its functionality remain unclear. This article investigated the effect of R-HFG, F-HFG, and MRPs on brain-gut peptides, gut microbiota, and digestive enzymes using an FD animal mode. After administration of R-HFG, F-HFG, and MRPs, higher mRNA expression level of gastrin (GAS) and lower mRNA expression level of vasoactive intestinal peptide (VIP) were exhibited in F-HFG and MRPs rats than R-HFG rats (P < .05). Furthermore, compared with the R-HFG group, the contents of motilin (MTL) and GAS showed an upward tendency, whereas the contents of VIP and chokcystokinin (CCK) showed a downward tendency in the F-HFG group. In addition, bacterial communities in the control, F-HFG, and MRPs groups clustered closely to one another, and bacterial communities in the model and recovery groups clustered together, whereas the bacterial communities in the R-HFG group were clustered into a category. Moreover, there were no apparent differences in brain-gut peptides and gut microbiota between the F-HFG and MRPs groups. However, after the oral administration of R-HFG, F-HFG, and MRPs, the level of digestive enzyme did not show a significant change as compared with the recovery group. These results indicated that the stronger effect of F-HFG could be attributed to the MRPs produced during stir frying, and MRPs possessed the effect of regulating brain-gut peptides and gut microbiota.

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