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Xiao Y.P.,Central South University | Pan Q.L.,Central South University | Pan Q.L.,Key Laboratory of Nonferrous Materials Science and Engineering | Li W.B.,Central South University | And 3 more authors.
Materials and Corrosion | Year: 2012

Corrosion behaviour of different tempers (namely NA, UA, PA and OA) of Al-Zn-Mg-Cu-Zr-Sc alloy was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), optical microscopy (OM) and transmission electron microscopy (TEM). Over aged (OA) can decrease the susceptibility to exfoliation due to the discontinuous distribution of the η precipitates at the grain boundaries, cause a negative shift of the corrosion potential (E corr), and lead to the prolonging of the time of the appearance of two time constants in impedance diagrams. In addition, Al-Zn-Mg-Cu-Zr-Sc alloy with over aged treatment has an enhanced resistance to exfoliation corrosion. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Xiao Y.P.,Central South University | Pan Q.L.,Central South University | Pan Q.L.,Key Laboratory of Nonferrous Materials Science and Engineering | Li W.B.,Central South University | And 4 more authors.
Materials and Corrosion | Year: 2012

The exfoliation corrosion behavior of an Al-Zn-Mg-Cu-Zr alloy containing Sc artificially aged at 120 °C for 24 h is studied by macroscopic observation techniques and electrochemical impedance spectroscopy (EIS) measurements. After 48 h immersion, the blisters start bursting and delamination initiates, along with the appearance of two time constants in the impedance diagrams. According to the simulation by equivalent circuit, the corrosion rate decreases sharply and then reaches a steady state, which is due to the change of the solution pH and oxide layer thickness, as well as the accumulation of corrosion products. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Gu L.,Central South University | Huang J.,Central South University | Huang J.,Key Laboratory of Nonferrous Materials Science and Engineering | Tang Y.,Central South University | And 2 more authors.
Journal of Alloys and Compounds | Year: 2015

Effects of different post treatments on microstructure and properties of WC-11 wt.% Co cemented carbides were investigated in this paper. The different post treatments that are carried out to the cemented carbides are (a) heating and quenching in oil bath, (b) controlled cryogenic treatment. Various mechanical and microstructural characterization of these alloys including density, coercive force, hardness, transverse rupture strength, phase composition, W solubility of the cobalt phase, martensitic phase transformation of the cobalt phase and WC grain shape were analyzed before and after post treatments. The experimental results show that post treatments have a significant influence on WC-Co cemented carbides and the details of the experimental study are presented in this paper. © 2014 Elsevier B.V. All rights reserved.


Zhang Y.,Central South University | Deng Y.,Central South University | Deng Y.,Key Laboratory of Nonferrous Materials Science and Engineering | Qi X.,Central South University | And 3 more authors.
Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research | Year: 2012

Two alloys with the different components of trace elements were prepared, and the effects of Sc on the microstructure and texture of Al-Zn-Mg-Cu alloys during hot deformation and solution treatment were investigated. Comparing with the alloy containing only trace Zr, alloy containing trace Sc and trace Zr exhibited following characteristics: after hot deformation, there are smaller sub-grains in the alloy; after solution treatment, the alloy has lower recrystalization fraction, and the density of {011} <211> (B-) orientation is stronger, while the density of {112} <111> (C-) orientation is weaker. For this reason above all-Al3(Sc, Zr) particles formed during homogenization distribute uniformly in both inner grain areas and grain boundary areas, which severely prohibited the migration of dislocations and grain boundaries during hot deformation and solution treatment. Because of interfacial energy offered from sub-grain boundaries, the precipitation behavior of MgZn2 was promoted. The promotion and strengthen of sub-microstructural result in increase of the final hardness of alloys with the different components of trace elements by 11.3%. © Copyright.


Deng Y.-L.,Central South University | Deng Y.-L.,Key Laboratory of Nonferrous Materials Science and Engineering | Wan L.,Central South University | Wu L.-H.,Central South University | And 3 more authors.
Journal of Materials Science | Year: 2011

In this study, the microstructural evolution of an as-cast Al-Zn-Mg-Cu alloy (AA7085) during various homogenization schemes is investigated. It is found that in a single-stage homogenization scheme, some of the primary eutectic gets transformed into the Al2CuMg phase at 400 °C, and the primary eutectic and Al2Cu phase gradually dissolve into the alloy matrix at 450 °C. The Al3Zr particles are mainly precipitated at the center of the grain because Zr is peritectic. However, the homogeneous distribution of the Al3Zr particles improves and the fraction of Al3Zr particles increases in two-stage homogenization scheme. At the first low-temperature (e.g., 400 °C) stage, the Al3Zr particles are homogeneously precipitated at the center of the grain by homogeneous nucleation and may be heterogeneously nucleated on the residual second-phase particles at the grain boundary regions. At the second elevated-temperature (e.g., 470 °C) stage, the Al3Zr nuclei become larger. A suitable two-stage homogenization scheme for the present 7085-type Al alloy is 400 °C/12 h + 470 °C/12 h. © Springer Science+Business Media, LLC 2010.

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