Papers by Author: Wei Ke

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Authors: Hua Mao Zhou, Jian Qiu Wang, Qi Shan Zang, En Hou Han, Wei Ke
Abstract: The acoustic emission (AE) detected during the fatigue process in an as-rolled magnesium alloy AZ31B was analyzed. Measurements were made during fatigue in air as well as in aqueous 0.1% NaCl solution. Three stages of fatigue were detected with AE. It is concluded that plasticity, crack extension or friction was the main AE sources during fatigue.
Authors: En Hou Han, Wan Qiu Zhou, Da Yong Shan, Wei Ke
Authors: Zhuo Qun Li, Da Yong Shan, Wei Ke, En Hou Han
Abstract: Microstructural examinations of T6-treated WE54 magnesium alloy were conducted after different aging conditions, and the influence of aging on electrochemical behavior of this alloy was investigated. For three batches of samples, with increasing aging time, the amount of precipitate phases was greatly promoted, and they formed in a strengthening continuous way. Electrochemical study showed that the value of corrosion potential followed the tendency to decrease when the aging condition transformed from under-aged to peak-aged. However, after peak-aging, the corrosion potential was raised to higher values. Explanations for the observed phenomena were based on the relationship between microstructure, especially precipitate phases, and electrochemical behavior. At under-aged condition, matrix served as galvanic cathode and precipitates acted as galvanic anode. Because the amount of precipitate would rise with prolonging aging time, it is natural that corrosion potential decreased. For over-aged alloys, metastable precipitate phases might in situ change to equilibrium phases, rendering increase of corrosion potential possible.
Authors: Rong Chang Zeng, En Hou Han, Wei Ke
Abstract: The fatigue crack propagation (FCP) behavior of magnesium alloy AZ61 at room temperature (RT), elevated temperature (60°C, 120°C) , and in ambient and wet air was investimated. The mechanisms of FCP were discussed in detail. It was demonstrated that The FCP rate of AZ61 magnesium alloy increased with increasing temperature and relative humidity (RH). Obvious change in the microstructure occurred during fatigue at elevated temperature, particularly at 120°C, compared to its original microstructure. Grain growth, deformation twin, grain boundary (GB) immigration and precipitates were observed in the microstructure at 120°C after fatigue. A bend occurred in the curves of FCP rate versus stress intensity factor at 120°C, which corresponded to a transition of failure mode from a mixed intergranular and transgranular fracture to a transgranular fracture. At first stage, the FCP rate increased sharply, and then went up slowly due to the growth of grain size. Secondary phase particles facilitated the fatigue crack initiation. The Hydrogen embrittlement (HE) may be primarily responsible for accelerating FCP rate in wet air.
Authors: Rong Chang Zeng, En Hou Han, Wei Ke
Abstract: This paper consists of a review of investigations and the factors affecting the fatigue of Mg and its alloys. The effect of materials, loading conditions and environmental factors on fatigue is discussed in detail. Particular attention has been paid to the influence of frequencies and the pH value of solutions on the fatigue life. The correlation between the threshold stress intensity factor range (ΔKth) and load ratio (R) for Mg alloy fatigue crack propagation (FCP) is summarized in a figure. Finally, the mechanisms of fatigue and corrosion fatigue (CF), crack initiation and crack propagation are also discussed.
Authors: Jian Chen, Jian Qiu Wang, En Hou Han, Wei Ke
Abstract: The corrosion of AZ91 magnesium alloy with residual stress was observed in-situ in an atmosphere of water vapor with cyclic wet-dry conditions using environmental scanning electron microscope (ESEM). The results showed that the oxygen concentration on the surface generally increased with the wetting time. And the average corrosion rate of AZ91 alloy with residual stress (RS) was much larger than that without RS, indicating RS accelerated corrosion. The corrosion localized at primary α-Mg area at short wetting time, but with the increase of wetting time spread to the eutectic α-Mg region. Small-size as-cast defects (<50μm) contributed little to the average corrosion rate while large-size as-cast defects (>100μm) influenced the distribution of water film and corrosion on the surface.
Authors: Wan Qiu Zhou, Da Yong Shan, En Hou Han, Wei Ke
Abstract: A phosphate conversion coating was deposited on diecast AZ91D magnesium alloys, the film was a complex phosphate containing Mg and Al,which showed amorphous structure. Corrosion resistance of conversion coating in 3.5%NaCl was investigated by polarization curve. It was showed that the anodic branch of polarization curve for the phosphate conversion coating presented typical passivation characteristic. Immersion test results showed that the corrosion rate of phosphate conversion coating was less than that of chromate Dow7 film.
Authors: Guang Bin Rao, Jian Qiu Wang, Wei Ke, En Hou Han
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