Papers by Author: Qian Li

Abstract: The oxidation kinetics of copper or aluminum added with magnesium was investigated by a modified Chou model. The effect of the addition of magnesium in copper or aluminum was discussed. The calculation results showed that the activation energy of CuMg0.34 was the highest among Cu-Mg alloys at 600-900 °C, which indicated that it had the best oxidation resistance in all of the samples. The aluminum alloy AA3004 containing 1.0 wt.% Mg showed the better anti-oxide behavior than AA5182 with 4.0 wt.% Mg, and the relation between oxidation rate and oxygen partial pressure could be expressed as 0.71 times power law.

Abstract: The high-temperature oxidation kinetics of Galvalume-coated steel sheet and Q235 steel sheet were studied by thermogravimetric analysis (TGA). A new diffusion equation was deduced and used to investigate their kinetic mechanism. The characteristic time (t_c) in the equation can be expressed as a function of temperature T, diffusion coefficient D⁰, thickness of the steel sheet H, etc. The calculated result showed that the oxidation reaction rate of Galvalume-coated steel sheet was slower than that of Q235 steel sheet through comparing the values of t_c. Besides, the oxidation reaction rate increased with the temperature rising from 750 to 850 °C. Compared our experimental data with the theoretical value calculated by the new function, a good agreement has been obtained.

Abstract: The high temperature oxidation and microstructure evolution of 55%Al-Zn-Si coated sheets were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). After oxidation, the coatings consisted of three phases including ZnO, Fe₂Al₅, and FeAl from topcoat to the substrate. The different diffusion rate of Fe and Al result in forming voids at the interface of intermetallic layer and the substrate. A good agreement has been reached between the experimental data and the calculation from Chou diffusion model, which has a good predicted function. Moreover, the characteristic oxidation time and the apparent activation energy were obtained.

Abstract: The phase equilibria in Al-rich corner of the Al-Zn-Ti ternary system at 400 °C were determined by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray powder diffraction (XRD). The results showed that this section consisted of three ternary-phase regions, namely, L+(Al)+τ, Ti₂Al₅+τ+(Al) and Ti₂Al₅+TiAl₃+(Al). The XRD patterns and EDS confirmed that a Ti₂Al₅-structured phase with containing 4 at.% Zn was stable at 400 °C. Furthermore, the ternary new phase (τ phase) was identified in samples and in equilibrium with (Al), Ti₂Al₅ and liquid, respectively.

Abstract: The isothermal section at 573 K of the Ni-Cu-La system was experimentally validated as well as the Mg-La-Cu system was thermodynamically evaluated. Four sample alloys in the Ni-Cu-La system were prepared and analyzed by ICP, XRD and BSE/EDS. All the experimental results were compared favorably with the calculated phase relationships. For the Mg-La-Cu ternary system, the isothermal section at 673 K was assessed on the basis of the available results in literatures, which showed a good agreement with the experimental data. Based on the thermodynamic models and parameters of the six binaries and four ternaries, the Mg-Ni-La-Cu system was finally modeled. The non-equilibrium solidification path La0.7Mg0.3Ni2.8-xCux (x=0-0.4) and the vertical section of LaNi5-Mg2Cu were calculated and analyzed from the viewpoint of hydrogen storage alloys design.

Abstract: The Mg₂NiH₄ hydrogen storage material was successfully prepared by controlled hydriding combustion synthesis (CHCS) from Mg and Ni powders in a high magnetic field. The effects of magnetic intensity on the structure, phase compositions and the hydriding/dehydriding (A/D) properties of the composite are investigated. As a result, a high magnetic field promotes the formation of Mg₂NiH₄. The PCT results show that the maximal hydrogen capacity at 573 K is 3.59 wt.%. The comparison of the hydrogen A/D results under the different conditions suggested that 4 T is the optimal magnetic intensity in our trial.

Abstract: The relationship between the morphology and protective action of hot-dip aluminizing coatings on Q235 steel have been investigated by SEM, EDS and EIS in 3.5 wt% NaCl aqueous solution. The results indicated that the anti-corrosion performance of the hot-dip aluminizing coatings using steel substrate rinsed by the distilled water at 25 oC was higher than that at 80 oC. The evolution of localized corrosion from pitting to exfoliation corrosion has been found on the aluminum coating surface during immersion, and corresponding equivalent circuit models were proposed to fit the EIS data in the initiation and propagation stages of corrosion process.

Abstract: A comparative study of the morphology and anticorrosive behaviour of commercial 55 wt% Al-Zn-Si coatings (CC) and hot-dip 55 wt% Al-Zn-Si coatings (HD) on Q235 steel was performed by using surface analysis techniques and electrochemical measurements. Despite the ingredients of the Al-rich dendritic phase for HD coating similar to the ingredients for CC coating, aluminum content in the Zn-rich phase for HD coating was almost twice higher than aluminum content for CC coating. The difference of surface morphologies and chemical compositions in Zn-rich phases for the two 55 wt% Al-Zn-Si coatings could significantly affect their corrosion properties. The corrosion behavior of the two coatings was investigated in 0.01 mol L-1 NaCl + 0.01 mol L-1 NaHSO3 aqueous solution. Both polarization curve and electrochemical impedance spectroscopy results indicate HD coatings had much higher corrosion resistance than CC ones.