组织结构对锌–铝–镁合金热浸镀层耐蚀性的影响

Effect of microstructure on corrosion resistance of hot-dip zinc–aluminum–magnesium alloy coating

以热浸镀Zn–3.25Al–2.35Mg和Zn–2.55Al–1.47Mg钢板为研究对象,分别采用扫描电镜、X射线衍射、辉光放电光发射光谱等方法对不同合金镀层的组织结构、物相组成、表面元素分布情况进行研究。以热镀锌层钢板作为对比,利用动电位极化曲线和电化学阻抗谱研究不同热浸镀钢板的腐蚀行为。结果表明,锌–铝–镁合金镀层主要由共晶组织、富锌相以及少量富铝相组成。不同成分镀层的组织结构存在差异,Zn–2.55Al–1.47Mg合金镀层表面的共晶相含量高于Zn–3.25Al–2.35Mg镀层,且在镀层的浅表层存在明显的富Mg区域。Zn–2.55Al–1.47Mg镀层的耐蚀性优于Zn–3.25Al–2.35Mg镀层,说明随锌–铝–镁镀层中共晶组织含量增大,合金镀层的耐蚀性提高。

The microstructure, phase composition and element distribution on surface of hot-dip Zn-3.25Al-2.35Mg and Zn-2.55Al-1.47Mg coated steel plates were studied by scanning electron microscopy, X-ray diffractometry, and glow discharge spectrometry. The corrosion behaviors of different hot-dip coated steel plates were studied by potentiodynamic polarization curve measurement and electrochemical impendence spectroscopy and compared with that of the hot-dip zinc coated steel plate. The results showed that the Zn-Al-Mg alloy coatings are mainly composed of eutectic phase, Zn-rich phase and a small amount orAl-rich phase. The alloy coatings with different compositions have different structures as shown by more eutectic phases in Zn-2.55Al-1.47Mg alloy coating than that in Zn-3.25Al-2.35Mg alloy coating, and the former has obvious Mg-rich area near the surface. The Zn-2.55Al-1.47Mg coating has better corrosion resistance than the Zn-3.25Al-2.35Mg coating, indicating that the corrosion resistance of Zn-Al-Mg alloy coating is improved with the increasing content of eutectic phase in it.