Papers by Author: En Hou Han

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Authors: Wei Neng Tang, Hong Yan, Rong Shi Chen, En Hou Han
Abstract: Superplastic deformation (SPD) behaviors of two fine-grained materials produced by ECAE and hot rolling methods have been contrastively studied in this paper. It is found that the optimum superplastic condition in as-ECAEed material was at 350°C and 1.7×10-3s-1 with elongation to failure about 800%; while in as-rolled material, the largest elongation to failure about 1000% was obtained at 480°C and 5.02×10-4s-1. Microstructure observation showed that grain evolution and cavitation behavior were different in these two materials during superplastic deformation. The controlled mechanisms for superplasticity, i.e. grain boundary sliding (GBS), dislocation creep and diffusional creep, at different deformation conditions were discussed in terms of strain rate sensitivity coefficient, stress exponent and activity energy.
Authors: Yong Wei Song, Da Yong Shan, En Hou Han
Abstract: Magnesium alloys are considered as “difficult to plate” metal. The pretreatment processes play a key role for plating. The pretreatments of alkaline cleaning, chromic acid etching and hydrofluoric acid activating were carried out and the microstructures investigated by SEM and EDAX in detail. The hydrofluoric acid activating time of 8 minutes was determined by Potential-Time curve. The experimental results showed that the alkaline cleaning moved the grease and oils off the substrate surface, but there was no apparent surface morphology change. The chromic acid etching was a very critical step, and the optimum etching time of 1 minute was chosen; the eutectic α was severely etched, and the chromic compounds were mainly formed on the surface. During the hydrofluoric acid activating, the white activating product of magnesium fluoride was preferentially generated on the β–phase, and obvious morphology change has been observed on the alloy substrate surface.
Authors: C.X. Dong, A.P. Xian, En Hou Han, J.K. Shang
Abstract: Carbon doped titanium dioxide photocatalysts have been synthesized by a precipitation method. Anatase TiO2 was obtained when the precipitate was heat-treated at 400°C when rutile phase appeared at 600°C. The absorption spectra of the powders showed strong absorption in visible region. For the sample calcined at 400 °C , the absorption extended up to 750nm. X-ray photoelectron spectrum (XPS) confirmed that carbon atoms were incorporated into the TiO2 crystal lattice. Photodegradation experiments showed that the powders had visible-light degradation activity.
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: Z.H. Huang, Rong Shi Chen, En Hou Han
Abstract: The potentials of Mg-Al system alloys for semi-solid forming have been extensively evaluated these years. In the present studies, mushy zone properties of the Mg-Zn system alloys, i.e. ZWx2 (x=2, 4, 6), are characterized and analyzed by using cooling curve thermal analysis method and continuous torque measurement technique. The results show that Tn1 (first characteristic temperature of primary crystal nucleation), Tn2 (second characteristic temperature of primary crystal nucleation) and Tch (temperature of dendritic coherency) decrease with the increasing of zinc content, and the temperature difference of (Tn1-Tn2) almost remains constant, while the temperature difference of (Tn2-Tch) changes dramatically when Zn content increases to 6wt.%; The results also show that the fs-cc (solid fraction of dendritic coherency) of ZWx2 alloys ranges from 0.4 to 0.51 while ZW22 and ZW62 alloys having higher fs-ch and ZW42 alloy having the lowest fs-ch; also, strength of alloys in mushy zone does not develop until a certain fraction solid( corresponding to the dendrite coherency point) is reached. The results obtained by cooling curve thermal analysis method and continuous torque measurement techniques are comparable to each other.
Authors: Rong Fa Zhang, Da Yong Shan, Rong Shi Chen, En Hou Han
Abstract: Micro arc oxidation is an effective method to improve corrosion resistance of magnesium alloys and the selected electric parameters have great effects on coating properties. In this paper, the effects of the unipolar pulse and the bipolar pulse on surface morphology, chemical compositions and corrosion resistance were studied. When working voltage was higher than breakdown voltage, sparks appeared on sample surface whether the unipolar pulse or the bipolar pulse was used. However, under the same positive working voltage, the spark size and lifetime obtained by the bipolar pulse were evidently larger and longer than those by the unipolar pulse, which resulted in rougher anodic coatings and worse corrosion resistance by the former than the latter.
Authors: En Hou Han, Wan Qiu Zhou, Da Yong Shan, Wei Ke
Authors: Y.Q. Ma, Rong Shi Chen, En Hou Han
Abstract: A new steel mold gravity casting magnesium alloy of low-cost, high strength, and high ductility has been developed and studied. This new magnesium alloy, which is designated as IMR-41, exhibits high strength (Yield Tensile Strength≈145 MPa, Ultimate Tensile Strength≈280 MPa) and high ductility (Elongation≈8%) at room temperature. The alloying elements are inexpensive ones and the cost of IMR-41 is similar to AZ91 series. The influence of small X element addition and heat treatment on the microstructures and mechanical properties are discussed. The IMR-41 combines the virtues of AZ91 series and AM60 series to some extend and shows great potential application on wheels of lightweight vehicles or motorcycles, etc. which require high strength and high ductility simultaneously.
Authors: Rong Shi Chen, Wei Neng Tang, Dao Kui Xu, En Hou Han
Abstract: The effects of Y addition to the Mg-Zn-Y-Zr alloy on the change of the microstructure and the mechanical properties (with the Y content range of 1 to 3 wt%) have been investigated. It shows that when Zn content is constant (5.65wt%), the alloys with Y content between 1.17 and 1.72wt% nearly reach its highest strength. With the composition near the optimums, the extruded Mg-6%Zn-1%Y-Zr alloy shows high strength and excellent ductility. The deformation behavior of this new alloy at high temperature has also been studied. Moreover, the super-long fatigue behavior of the Mg-6%Zn-1%Y-Zr alloy has also been tested, the results show the alloy with a high fatigue strength of about 85-90MPa in the super-long fatigue life regime of 1×109 cycles.
Authors: Gui Ying Sha, Yong Bo Xu, En Hou Han
Abstract: The dynamic experiments for the Mg-Li alloys with single phase structure were carried out using the Hopkinson pressure bar. The dynamic crack propagation behavior and fracture mechanism of the alloys were investigated. The results show that the dynamic crack propagation is a deceleration process for the Mg-Li alloys under high loading rate. The fastest crack propagation velocity for Mg-3.3Li alloy is m/s 37 . 1253 , and 935.36m/s for Mg-14Li alloy. Observations of the fracture by SEM reveal that the dynamic fracture surface for Mg-3.3Li alloy mainly appears to be brittle fracture along grain boundaries. Whereas, the Mg-14Li alloy is ductile fracture mode under high loading rate. The main reason for these may be the transformation of hcp→bcc structure and the precipitation of the MgLi2Al and AlLi, as increase of Li in Mg-Li alloy.
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