Morphological and Microstructural Characterization of the Aragonitic CaCO3/Mg,Al-Hydrotalcite Coating on Mg-9 Wt Pct Al-1 Wt Pct Zn Alloy to Protect against Corrosion

作者：Uan Jun Yen^*; Yu Bing Lung; Pan Xin Liang

来源：Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, 2008, 39A(13): 3233-3245.

DOI：10.1007/s11661-008-9669-0

This work presents a novel environmentally clean method for synthesizing the chemical conversion coating on Mg-Al-Zn (AZ91D) alloy surface and protecting the alloy from corrosion. An aragonitic CaCO3/Mg,Al-hydrotalcite two-layer coating was first developed on the Mg alloy in an aqueous Ca2+p/HCO3 - solution at 50C. When the Mg sample was immersed in a Ca2+/HCO3 - aqueous solution, corrosion occurred on the Mg sample surface, resulting in a high interfacial Mg2+p concentration and high pH value directly above the sample surface. The layer (Mg,Al-hydrotalcite) generated by corrosion formed on the Mg alloy when initially immersed in the Ca2+/HCO3 - solution. Temperature, solution pH, and presence of Mg2+ are important factors when determining the production yield of aragonitic CaCO3 particles. In this work, the high interfacial Mg2+ concentration and high pH directly above the sample surface induced preferential growth of CaCO3 on the Mg,Al-hydrotalcite layer, thereby forming a two-layer coating on the Mg alloy sample. Electrochemical tests using the polarization impedance method and salt spray test show that the CaCO3 coating protected the substrate metal from corrosion. Moreover, the CaCO3 layer markedly improved the galvanic corrosion resistance of the coated Mg alloys.

• 出版日期2008-12