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.

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.

Microstructure Evolution of High-Alloyed Al–Zn–Mg–Cu–Zr Alloy Containing Trace Amount of Sc During Homogenization

Yu Wang,Zhihui Li,Baiqing Xiong,Kai Wen,Shuhui Huang,Xiwu Li,Yongan Zhang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.3

Microstructure evolution of a new high-alloyed Al–Zn–Mg–Cu–Zr–Sc aluminium alloy during two-stage homogenizationprocess was investigated by use of scanning electron microscope, transition electron microscope and high resolution transitionelectron microscope. The results indicate that the morphology and chemical composition of Al 3 (Sc, Zr) particles formedin the fi rst stage were greatly aff ected by heating temperature. With the increase of heating temperature, the morphologyof Al 3 (Sc, Zr) particles transform from cuboidal with evident faceting to spheroidal due to improved Zr diff usivity. MoreZr atoms enrich in the interface of precipitate/matrix forming a thin layer. Moreover, the mean diameter of precipitatesincreases a little bit with the increase of heating temperature, showing very restricted coarsening rate and high thermal stabilityof Al 3 (Sc, Zr) particles. After an appropriate second stage heat treatment (474 °C × 48 h), the intermetallic formed inthe solidifi cation process could dissolve suffi ciently and Al 3 (Sc, Zr) particles still keep very good coherency with Al matrixwithout abnormal growth.

Codon Optimization, Soluble Expression and Purification of PE_PGRS45 Gene from Mycobacterium tuberculosis and Preparation of Its Polyclonal Antibody Protein

( Tao Xu ),( Minying Li ),( Chutong Wang ),( Meili Yuan ),( Xianyou Chang ),( Zhongqing Qian ),( Baiqing Li ),( Meiqun Sun ),( Hongtao Wang ) 한국미생물 · 생명공학회 2021 Journal of microbiology and biotechnology Vol.31 No.11

Studies have demonstrated that PE_PGRS45 is constitutively expressed under various environmental conditions (such as nutrient depletion, hypoxia, and low pH) of the in vitro growth conditions examined, indicating that PE_PGRS45 protein is critical to the basic functions of Mycobacterium tuberculosis. However, there are few reports about the biochemical function and pathogenic mechanism of PE_PGRS45 protein. The fact that this M. tuberculosis gene is not easily expressed in E. coli may be mainly due to the high content of G+C and the use of unique codons. Fusion tags are indispensable tools used to improve the soluble expression of recombinant proteins and accelerate the characterization of protein structure and function. In the present study, His6, Trx, and His6-MBP were used as fusion tags, but only MBP-PE_PGRS45 was expressed solubly. The purification using His6-MBP tag-specific binding to the Ni column was easy to separate after the tag cleavage. We used the purified PE_PGRS45 to immunize New Zealand rabbits and obtained anti- PE_PGRS45 serum. We found that the titer of polyclonal antibodies against PE_PGR45 was higher than 1:256000. The result shows that purified PE_PGRS45 can induce New Zealand rabbits to produce high-titer antibodies. In conclusion, the recombinant protein PE_PGRS45 was successfully expressed in E. coli and specific antiserum was prepared, which will be followed by further evaluation of these specific antigens to develop highly sensitive and specific diagnostic tests for tuberculosis.

A Voltage Stability Analysis Method of Multi-infeed HVDC Power Systems

Shao, Yao,Tang, Yong,Zhang, Jian,Li, Baiqing The Korean Institute of Electrical Engineers 2014 The Journal of International Council on Electrical Vol.4 No.1

According to the Chinese power network planning, the risk of voltage instability at the receiving-end AC power system will be increased significantly, where there will be more HVDC systems feeding into a same AC grid in the future. At present, the effective voltage stability analysis methods of multi-infeed DC (MIDC) system are few, the most widely used method with most research results is the multi-infeed short-circuit ratio (MISCR) index at home and abroad. The deficiency of MISCR index is pointed out. The relationship between multi-infeed interaction factor (MIIF) and the voltage stability of the receiving-end AC system is discussed. Then a new method joint MIIF and MISCR indexes to evaluate the voltage stability of MIDC system is put forward. Finally, simulation tests and analysis results of a large actual grid prove the feasibility and good performance of the proposed new method.

Short-term Reactive Power Reserve Optimization Based on Trajectory Sensitivity

Quancai Sun,Haozhong Cheng,Jian Zhang,Baiqing Li,Yue Song 대한전기학회 2017 Journal of Electrical Engineering & Technology Vol.12 No.2

An increasing concern is paid to short-term voltage stability with the growth of penetration of induction motor loads. Reactive power reserve(RPR) of power system is critical to improve voltage stability. A definition of short-term voltage stability-related RPR SVRPR) is proposed. Generators vary their contributions to voltage stability with their location and system condition, etc. Voltage support coefficient based on the second-order trace sensitivity method is proposed to evaluate SVRPR’s contribution to short-term voltage stability. The evaluation method can account for the generator’s reactive support in transient process and the contingency severity. Then an optimization model to improve short-term voltage stability is built. To deal with multiple contingencies, contingency weight taking into account both its probability and severity is proposed. The optimization problem is solved by primal dual interior point method. Testing on IEEE_39 bus system, it is indicated that the method proposed is effective. Short-term voltage stability is improved significantly by the way of SVRPR optimization. Hence, the approach can be used to prevent the happening of voltage collapse during system’s contingency.

Short-term Reactive Power Reserve Optimization Based on Trajectory Sensitivity

Sun, Quancai,Cheng, Haozhong,Zhang, Jian,Li, Baiqing,Song, Yue The Korean Institute of Electrical Engineers 2017 Journal of Electrical Engineering & Technology Vol.12 No.2

An increasing concern is paid to short-term voltage stability with the growth of penetration of induction motor loads. Reactive power reserve(RPR) of power system is critical to improve voltage stability. A definition of short-term voltage stability-related RPR(SVRPR) is proposed. Generators vary their contributions to voltage stability with their location and system condition, etc. Voltage support coefficient based on the second-order trace sensitivity method is proposed to evaluate SVRPR's contribution to short-term voltage stability. The evaluation method can account for the generator's reactive support in transient process and the contingency severity. Then an optimization model to improve short-term voltage stability is built. To deal with multiple contingencies, contingency weight taking into account both its probability and severity is proposed. The optimization problem is solved by primal dual interior point method. Testing on IEEE_39 bus system, it is indicated that the method proposed is effective. Short-term voltage stability is improved significantly by the way of SVRPR optimization. Hence, the approach can be used to prevent the happening of voltage collapse during system's contingency.