Papers by Author: Wei Min Mao

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Authors: Zheng Liu, Wei Min Mao
Abstract: The semi-solid A356 alloy slurry is prepared by compound process, and the effect of the compound process on morphology and size of primary α-Al in A356 alloy is researched. The results indicate that the compound process remarkably affects the morphology and the size of primary α-Al. Primary α-Al with particle-like is distributed uniformly in A356 alloy, and there is no the transient area of change in structure morphology. Compared with the samples prepared by low superheat pouring and slightly electromagnetic stirring, the nucleation rate, morphology and grain size of primary α-Al in A356 alloy are markedly improved by the compound process. The mechanism of refining grain in the compound process is probed.
Authors: Wei Min Mao, Y. Li, Ping Yang, W. Guo
Abstract: The possible mechanisms concerning abnormal growth of Goss grains in grain oriented electrical steels were investigated. The density of inhibitor particles near sheet surface, where the Goss grains located, was lower than that in center layer before secondary recrystallization, and the grains near surface could grow more easily because of reduced pinning effect. Few Goss grains could survive the growth competition and reach the sheet surface, after which the inhibitor particles inside the Goss grains coarsened slower. The phenomenon resulted in easy growth of the Goss grains at the expense of smaller neighboring grains while they could hardly be consumed by larger neighboring grains during the high temperature secondary recrystallization. Very large final size of the Goss grains was then obtained. The mechanisms were discussed based on the hot rolling characteristics and the elastic anisotropy of the ferrite matrix.
Authors: Li Meng, Ping Yang, Zude Zhao, Wei Min Mao
Abstract: Orientation mapping based on EBSD technique was applied to analyze the rules of orientation evolution of grains in AZ31 magnesium alloy. Results show that not only under deformation strain rate of 1×10-2s-1, but under 4×10-4s-1(the superplastic deformation condition), grains in all samples with initial textures rotate gradually to near basal orientation ({0002} || compression plane) at different ways, and basal texture becomes stronger with increasing strain, which indicates plastic slip plays an important role during hot deformation. Otherwise, no evident non-basal pyramidal slip of as some studies mentioned was observed in the sample with the initial basal texture, and the basal orientation is kept unchanged during the deformation process, which suggests that basal slip is the uppermost plastic slip mechanism in this sample. In addition, the phenomenon of viscous laminar flow was observed in the sample with initial basal texture.
Authors: Ping Yang, Li Meng, Wei Min Mao, Leng Chen
Abstract: Orientation mapping based on EBSD technique was applied to reveal the orientations of new grains and their relationships to the surrounding matrices, to analyze Kikuchi band contrast and the influence of strain rates on local orientation evolution. This information is used to understand the dynamic recrystallization mechanism and the relative contribution of plastic slip versus grain boundary glide or grain rotation related with super-plasticity. For this purpose samples with different initial textures were deformed by (quasi-)plain strain compression at two strain rates. It is suggested that the dynamic recrystallization in this alloy proceeds in continuous way by progressive subgrain rotation. No evident non-basal slip of was observed by referring texture evolution in the sample with initial basal texture. A high strain rate promotes more contribution of plastic slip accompanied by fast orientation changes. The fact that groups of grains with very similar orientations in basal oriented samples is discussed in terms of viscous flow.
Authors: Zhen Lin Zhang, Zhi Feng Zhang, Jun Xu, Hao Zhang, Wei Min Mao
Abstract: Stir casting is a near net shape process that can cast the composite components directly. Fluidity is an important factor for mold filling in casting process, but the fluidity of composite slurry is poor due to the addition of SiCp. In this research, SiCp/A357 composites with 20wt.% SiCp were manufactured by mechanical stir casting. Effect of mechanical stirring and air pressure on the fluidity of SiCp/A357 composites were investigated with eight thin flow channels. The fluidity was compared at different rotating speed and air pressure. The results showed that the fluidity increased with rotating speed, which was more obvious in semi-solid interval. It was noticed that the fluidity decreased with air pressure, the gas involving and the cooling speed were aggravated with air pressure increasing, which reduced the fluidity.
Authors: Zheng Liu, Xiao Mei Liu, Wei Min Mao
Abstract: The evolution of microstructural morphology in semisolid A356 alloy was researched under the mechanical stirring. The results showed that there was the effect of the stirring time on the microstructural morphology of semisolid A356 alloy, in which the microstructural morphology became better with the stirring time prolonging. There was also the effect of the stirring process on the microstructural morphology, in which the microstructural morphology obtained from the melt cooling to the reset solid volume fraction to start stirring was coarser than that obtained from the stirring above the liquidus temperature, but the microstructural morphology rapidly changes under the shearing force.
Authors: Zisu Zhao, Wei Min Mao, Dierk Raabe
Authors: Leng Chen, Wei Min Mao, H.P. Feng, Yong Ning Yu
Authors: H.P. Feng, H.X. Zhu, Wei Min Mao, Leng Chen, Fan Xiu Lu
Abstract: Free-standing CVD diamond films were prepared under the substrate temperature in the range of 850-1050oC. Macro- and micro-textures of the films were investigated based on the SEM observation as well as on the ODF and EBSD analysis. It was found that certain growth selection process appeared during diamond deposition which, however, did not lead to a strong film texture. It is indicated that strong fluctuation of growth ratio V<100>/V<111> and frequent growth twinning during film deposition resulted in randomization effect of grain orientations, which can be transformed by adjusting the parameters of film preparation.
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