AZ31镁合金微弧氧化陶瓷层表面Mg(OH)2膜层的制备及耐蚀性

采用不同浓度的NaOH溶液对AZ31镁合金微弧氧化(Micro-arc oxidation, MAO)陶瓷层进行水热处理, 研究了水热溶液浓度对MAO陶瓷层组织结构及耐蚀性能的影响, 探讨了水热成膜及膜层的腐蚀机理。研究结果表明：水热处理过程中MAO陶瓷层表面的MgO部分溶解, 释放出的Mg ²⁺与水热溶液中的OH ^-结合形成Mg(OH)₂纳米片沉淀在陶瓷层表面及孔洞内。随着水热溶液中NaOH浓度的增加, 水热处理过程中形成的Mg(OH)₂将MAO陶瓷层表面的孔洞及裂纹等固有缺陷闭合, 提高了膜层的致密性。电化学实验结果表明, MAO及水热复合处理所制备的Mg(OH)₂/MAO复合膜层比单一MAO陶瓷层具有更好的耐蚀性, 而且随着NaOH浓度的提高, Mg(OH)₂/MAO复合膜层的耐蚀性增强; 浸泡实验结果表明Mg(OH)₂/MAO复合膜层能为镁合金基体提供长久的腐蚀防护保护能力。

Mg(OH)2 Film on Micro-arc Oxidation Ceramic Coating of AZ31 Magnesium Alloy: Preparation and Corrosion Resistance

The micro-arc oxidation (MAO) ceramic coating on AZ31 magnesium alloy was treated by hydrothermal treatment in NaOH solution to study the effect of the concentration of NaOH solution on the microstructure and corrosion resistance of the obtained Mg(OH)₂/MAO composite coating, the formation mechanism and the corrosion mechanism of the hydrothermal film was annalysed at the same time. The results showed that MgO in the surface of MAO ceramic layer was partially dissolved during hydrothermal reaction. And the released Mg ²⁺ was combined with OH ^- in hydrothermal solution to form Mg(OH)₂ nanosheets which deposited on the surface of ceramic layer and inner wall of the pores. With increasing of NaOH concentration of the hydrothermal solution, more Mg(OH)₂ formed during hydrothermal reaction and sealed the inherent defects such as pores and cracks in the MAO ceramic layer, which improved the compactness of the coating. In addition, the electrochemical test results demonstrated that the Mg(OH)₂/MAO composite coating prepared by MAO and hydrothermal treatment achieved better corrosion resistance than the single MAO ceramic layer, and the corrosion resistance of Mg(OH)₂/MAO composite coating increased with the increasing concentration of the hydrothermal solution. And the immersion test showed that Mg(OH)₂/MAO composite coating could provide long-term corrosion protection for magnesium alloy.