The activating process of Al-Sn alloys in alkaline solution is investigated by electrochemical measurements, and their structure and morphology are analyzed by X-ray diffraction(XRD) and scanning electron microscope(SEM). A vigorous potential fluctuation process which is composed of a great amount of V-shape potential barrancas is observed during the galvanostatic discharging process.When discharged at the stable potential platform of V-shape potential barrancas, a great amount of arc-shape protuberances exists on the surface of the anode. When discharged at the bottom of the V-shape potential barranca, a lot of micropores and micro cracks exist on the surface of the anode. An explanation for the potential fluctuation is proposed. Higher Sn content is necessary for the formation of micro cracks in the hydroxide film which is formed on the surface of the anode, which results from the mismatch in the size and structure between SnO 3 2− ions and Al(OH) 3 . The formation, propagation and convergence of the micro cracks and the rupture of the film all need a strong internal stress in the film, which relies on the thickness of the film. The thickness of the film depends on the discharging current density.
Bi, a group 15 element, was added to magnesium alloys and applied to seawater batteries in marine operating machinery to improve the electrochemical performance and corrosion resistance of the battery. The electrochemical properties of as-cast pure Mg, Mg–8Al, and Mg–8Al–xBi alloy anodes in 3.5% NaCl solution were researched. Electrochemical impedance spectroscopy and an immersion test in 3.5% NaCl solution show that the Mg–8%Al–0.4%Bi alloy provides better corrosion resistance than Mg and the Mg–8Al alloy. The galvanostatic discharge results show that the Mg–8%Al–0.4%Bi alloy revealed better electrochemical properties and utilization efficiency in 3.5% NaCl solution. The Mg17Al12 and BiOCl phases formed during the discharge process of the Mg–8%Al–0.4%Bi alloy play an important role in improving the electrochemical performance and utilization efficiency of the alloy.
Laser-cladding CoCrFeMoNi high-entropy alloy coating is composed of face-centred cubic, σ and µ phases. After annealing at 700 °C, many needle-like precipitates of the σ phase are found in the FCC solid solution, and the granular µ phase precipitated at the edge of the primary net-structural σ phase. After annealing at 800 °C, granular µ phases are found inside the primary σ phase. The friction coefficients of the coatings (as-cladded, as-annealed at 700 °C and 800 °C) decrease dramatically compared with the substrate of H13 steel. Obvious spheroidising of the σ phase at 900 °C leads to a decrease of hardness and an increase of friction coefficient. Furthermore, the CoCrFeMoNi high-entropy coatings show better corrosion resistance than H13 steel in 3.5 wt-% NaCl solution.
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