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通过SEM、TEM和电化学测试方法研究了Zn-1.2Sb合金中富Sb相的微观结构和电化学性质。结果表明,Zn-1.2Sb合金中的富Sb第二相Sb∶Zn原子比约为2∶3,但其晶体结构与Sb₂Zn₃不同。在不同的pH值环境中,电化学测试显示富Sb相的电化学活性比Zn低。富Sb相对Zn耐蚀性的影响有明显差异,在近中性0.1 mol/L NaCl (pH=6.5)溶液中,富Sb相对纯Zn的腐蚀过程作用不明显,对阳极和阴极氧还原反应均没有显著的促进作用;在酸性0.1 mol/L NaCl (pH=3)溶液中,富Sb相显著促进阴极析氢反应,导致锌合金耐蚀性能变差。

In the process of hot-dip galvanizing, some beneficial alloying elements are deliberately added to the molten Zn bath, in order to improve the coating properties, such as formability and corrosion resistance. Sb is one of the interesting alloying additions to the Zn bath, as it can decrease the viscosity and the surface tension of the molten Zn, contributing to producing a uniform Zn coating. Due to the low solid solubility of Sb in molten Zn at galvanising temperature, Sb-rich intermetallic particles were always found in the galvanized layers. The presence of Sb-rich phases may affect the structural properties and corrosion performance of galvanized coating. In the literature, it was reported that small addition of Sb has no significant effect on the structure and growth of galvanized layers, but a higher amount (>1%, mass fraction) of Sb can promote the dendritic solidification of Zn. In order to understand the mechanism of Sb addition on the structure and growth of galvanized coating, it is essential to identify the crystal structure of Sb-rich phases. It was reported that the Sb-rich phases found in the η layer of a galvanized coating corresponds to the electron diffraction patterns of Sb₂Zn₃. However, some researchers hold that the Sb₂Zn₃ compound does not exist at room temperature, since it can transform to Sb₃Zn₄ and Zn at some elevated temperature. Consequently, in this work, the structure of Sb-rich intermetallic phase in the Zn-1.2Sb (1.2%Sb) alloy has been investigated by SEM and TEM. SEM/EDS showed that Sb is present in the form of Sb-rich intermatallic phase and there is no detectable Sb in the Zn solid solution. Transmission electron diffractions analysis and EDS results indicated that the composition of Sb-rich intermatallic phases is close to that of Sb₂Zn₃, whereas the structure is totally different from the latter. The corrosion resistance of Zn-1.2Sb alloy has been analysed by electrochemcial polarization measurements in the different solutions. The analysed results showed that the Sb-rich phase has no obvious effect on the oxygen reduction reaction, in the aerated 0.1 mol/L NaCl (pH=6.5) solution. However, the Sb-rich phase can promote the hydrogen evolution reaction, in the deaerated acidic solution (0.1 mol/L NaCl, pH=3). Corrosion pits were found in the Zn matrix around the Sb-rich phases by SEM observations, which indicate that Zn has higher activity than Zn-Sb phase.