水热处理对AZ31镁合金微弧氧化陶瓷层组织结构及耐蚀性的影响

Effect of Hydrothermal Treatment on Microstructure and Corrosion Resistance of Micro-arc Oxidization Ceramic Layer on AZ31 Mg-alloy

采用两种不同成分的溶液对AZ31镁合金微弧氧化(MAO)陶瓷层进行125℃+18 h的水热处理,研究了水热溶液成分对微弧氧化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腐蚀机理。研究结果表明:水热处理过程中微弧氧化陶瓷层表面的MgO部分溶解,释放出的Mg2+与碱性水热溶液中的OH-结合形成Mg(OH)2纳米片沉淀在陶瓷层表面及孔洞内;而在含有Al3+和Co2+的溶液处理过程中,溶液中的Al3+和Co2+取代沉淀在MgO表面及孔洞内的Mg(OH)2中部分Mg2+的位置形成双金属氢氧化物(LDH)纳米片,将微弧氧化陶瓷层表面的孔洞及裂纹缺陷闭合。润湿性与电化学测试结果表明,亲水性的Mg(OH)2/MAO复合膜层因Mg(OH)2对MAO陶瓷层的封孔效应能在一定程度上提高MAO陶瓷层的耐蚀性,而疏水性的LDH/MAO复合膜层因封孔效应和LDH离子交换能力能显著提高MAO陶瓷层的耐蚀性。

The micro-arc oxidization(MAO)ceramic layer on AZ31 Mg-alloy was post-treated by hydrothermal treatment at 125℃for 18 h with two solutions of different compositions.The effect of hydrothermal solutions on the microstructure and corrosion resistance of MAO ceramic layer was studied,and the relevant formation-and corrosion-mechanism of the film generated via hydrothermal treatment were discussed.The results show that MgO on the MAO ceramic layer was partially dissolved during hydrothermal treatment,and the released Mg2+was combined with OH-in alkaline hydrothermal solution to form Mg(OH)2 nanosheets,which deposited on the surface of ceramic layer and pores;whereas Al3+and Co2+in the other solution might replace some Mg2+in Mg(OH)2 to form layered double hydroxides(LDH)nanoplates,which could seal the micro-poles and cracks on the MAO ceramic layer.Wettability and electrochemical test results show that the sealing effect of hydrophilic Mg(OH)2 coating on MAO ceramic layer can improve the corrosion resistance of MAO ceramic layer to some extent.However,hydrophobic LDH coating can significantly improve the corrosion resistance of MAO ceramic coating due to the sealing effect and the ion exchange ability of LDH.