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Zhang Y.,Beijing University of Technology | Gao K.,Beijing University of Technology | Wen S.,Beijing University of Technology | Huang H.,Beijing University of Technology | And 2 more authors.
Journal of Alloys and Compounds | Year: 2014

The aging strengthening behavior and coarsening process of Al3Er precipitates were investigated in Al-0.045Er (in at.%) alloys aged isothermally at 300-400 °C, using Vickers micro-hardness measurement and transmission electron microscopy (TEM) observation. The isothermal hardness curves showed that the peak hardness decreased slightly with the increase of temperature. From the TEM observations, the radius of Al3Er precipitates at peak hardness was measured to be 2.4 ± 0.4 nm. The coherency of Al 3Er precipitates started to get lost at the radius of 8.0-9.1 nm, which were much larger than the predicted value. The difference was speculated to be due the reduction of misfit between Al3Er precipitates and matrix when particles were very small. From the analysis of the coarsening of coherent Al3Er particles using LSW theory, the diffusion activation energy and the diffusivity pre-exponential constant of Er in Al were deduced to be 77.2 ± 5.3 kJ/mol and (4.3 ± 2.2) × 10-12 m2 s-1, respectively. Finally, the strength increment caused by Al3Er particles was evaluated using precipitation strengthening theory. It was found that when the particle radius was larger than 2.4 nm, the Orowan bypass mechanism dominated. In radius of 0-1.4 nm, a less coherency strengthening contribution indicated a reduction of lattice misfit between particles and matrix. From the strength plateaus in radius of 1.4-2.4 nm, the anti-phase boundary (APB) energy of Al3Er precipitates was deduced to be 0.60 ± 0.03 J/m2. © 2014 Elsevier B.V. All rights reserved. Source

Zhang Y.,Beijing University of Technology | Gao K.,Beijing University of Technology | Wen S.,Beijing University of Technology | Huang H.,Beijing University of Technology | And 4 more authors.
Journal of Alloys and Compounds | Year: 2014

The solubilities of Er and Yb in Al at high temperature were evaluated from the electrical resistivity measurement, from which the Delta;S and Delta;H were estimated to be 3.0 plusmn; 0.1k and -0.86 plusmn; 0.01 eV for Al-Er alloys, 3.7 plusmn; 1.0k and -0.93 plusmn; 0.07 eV for Al-Yb alloys, respectively. The solubility curves of Er and Yb therefore could be obtained. According to the solubility curves of Er and Yb, on the one hand, the largest volume fractions of Al3Er, Al3Yb at room temperature were calculated to be 0.18%, 0.10%, respectively, which were obviously less than that of Al 3Sc, i.e., 0.92%. On the other hand, the free energy per unit volume for the nucleation of trialuminides was evaluated with the consideration of Gibbs-Thomson effect. According to the obtained chemical driving force, the corresponding critical radius, critical nucleation energy and the steady state nucleation rate could be further calculated. The results indicated that in the binary alloys with the same concentration at the same temperature, comparing with Al3Sc, Al3Yb and Al3Er showed smaller critical radius and larger steady state nucleation rate, which implied that in Al-Yb and Al-Er alloys, higher number density of fine precipitates would be possibly existed. © 2014 Published by Elsevier B.V. Source

Zhou D.,Yin Bang Clad Material Co. | Chen Z.,Central South University | Zhang X.,Central South University | Tang J.,Central South University
Jinshu Rechuli/Heat Treatment of Metals | Year: 2014

The Al-Si alloy/low-carbon steel clad plates bonded by cold-rolling were annealed at different temperatures and time. Silicon's effect on the formation of the intermetallic compound (IMC) in the interface was investigated by use of optical microscope (OM), scanning electron microscope (SEM) and EDAX energy dispersive spectrometer. The results show that the clad plates with 0.67wt% of Si additions have the best effect for preventing the growth of the IMC layer, which has the highest IMC critical forming temperature of 615°C. But when Si additions is more than 1.62wt%, it decreases the melting point of Al-Si alloy, increases the element diffusion rate in Al-Si alloy, accelerate the IMC growth, and the structures of IMC are τ6-Al8Fe2Si + τ5-Al4.5FeSi + η-Al5Fe2. Source

Zhou D.-J.,Yin Bang Clad Material Co. | Yin L.,Central South University | Zhang X.-M.,Central South University | Tang J.-G.,Central South University | Liu X.-X.,Central South University
Zhongguo Youse Jinshu Xuebao/Chinese Journal of Nonferrous Metals | Year: 2012

The aluminum/stainless steel clad plates bonded by hot-rolling were annealed at different temperatures for different times. The microstructure, element distribution and identification of the intermetallic compound (IMC) at the interface were studied with Zeiss Ax10 optical microscope, Quanta-200 scanning electron microscope, EDAX energy dispersive spectrometer, D-max XRD, respectively. The influence of annealing temperature and time on the formation and growth of the IMC at the interface was investigated. The results show that the IMC (Fe 2Al 5) forms at the interface, which begins to form when the temperature is up to 773 K. With elongation of the annealing time, it becomes thicker according to the parabolic law. The growth activation energy for the growth of the compound is 162.3 kJ/mol, and the growth kinetics model is obtained, by which the thickness of the IMC can be evaluated. Source

Gao C.,Yin Bang Clad Material Co. | Li L.,Yin Bang Clad Material Co. | Chen X.,Yin Bang Clad Material Co. | Zhou D.,Yin Bang Clad Material Co. | Tang C.,Guangdong University of Technology
Materials and Design | Year: 2016

The effect of surface preparation on the bond strength of Al-St clad strips in cold roll bonding (CRB) was investigated. For the purpose, the steel strip were prepared by two different way before the cold roll bonding, and evaluate the sample bonding strength by peeling test of the rolling deformation zone. The results show that, at the same reduction, bond strength of Al-St strip treated by belt grinding is higher than by wire brushing. The threshold reduction of Al-St strip treated by belt grinding (10%) is lower than by wire brushing (15%). The belt grinding treatment removes contamination such as oxide layer efficiently and has proper degree of surface hardened. The strip surface with thinner brittle layer and cleaner metal can create stronger bonding. A major feature of the bonding mechanism is that soft aluminum is extruded into the cracks on steel surface under normal roll pressure and contacts with underlying fresh steel metal so that the metallic bond between Al and Fe is formed. Meanwhile the mechanical biting from the blocks along the interface also contributes to the bonding strength. © 2016 Published by Elsevier Ltd. Source

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