镁合金微弧氧化涂层表面原位制备MgCr-LDH纳米层及其耐蚀机理研究

In-Situ Preparation of MgCr-LDH Nano-Layer on MAO Coating of Mg Alloy and Its Anti-Corrosion Mechanism

为了进一步提升镁合金耐蚀性,将水滑石(layered double hydroxides,LDH)与微弧氧化(MAO)涂层结合制备一种主动防护的高耐蚀复合涂层。采用原位法在AZ31镁合金MAO涂层表面制备了层间含NO3^-的MgCr-LDH层,构成LDH/MAO复合涂层,研究原有MAO涂层表面LDH的微观组织结构及其与原始MAO涂层的相互作用,并利用长时间浸泡法和电化学法测试MgCr-LDH/MAO复合涂层试样在3.5%NaCl(质量分数)溶液中的耐蚀性能,揭示LDH层耐蚀机理,研究结果显示:LDH易于在镁合金表面MAO层的孔洞中形成,最终生成均匀致密片状结构的层。LDH的原位生长过程对原始MAO涂层没有破坏,MgCr-LDH与MAO涂层之间属于化学结合,具有强的粘附性与机械稳定性。MgCr-LDH/MAO复合涂层明显提高了AZ31镁合金的耐腐蚀性能,LDH层的耐蚀机理主要表现为两部分,一是LDH均匀形成于原始MAO层上,有效地覆盖了MAO层的孔洞与裂纹,阻挡氯离子通过MAO涂层的固有缺陷进入合金基体产生破坏;二是LDH的硝酸根层间阴离子能够与腐蚀环境中的氯离子进行离子交换,降低溶液中的氯离子浓度,从而延长涂层的耐蚀性。

A highly corrosion-resistant and active-protection composite coating was prepared using layered double hydroxides(LDH)layer and micro-arc oxidation(MAO)to further improve the anti-corrosion property of Mg alloy.MgCr-LDH/MAO composite coating was prepared through in-situ growing LDH layer including NO3-on the surface of MAO coating.The morphology,composition and microstructure of the MgCr-LDH/MAO composite coating were characterized by XRD,XPS,FT-IR,SEM,and the interaction between LDH and original MAO coating was investigated.The anti-corrosion properties of the MgCr-LDH/MAO coating were tested through immersion in 3.5%NaCl(mass fraction)solution and electrochemical experiments.The results show that the LDHs form a dense sheet-like layer on the original MAO coating surface,which can effectively cover the inherent defects of MAO coating,and LDH layer is preferentially formed in the pores of original MAO coating.LDHs do not damage the original MAO coating during the growth process,and the adhesion of LDH layer and MAO layer are strong and stable.The composite coating shows the optimum corrosion protection,since MgCr-LDH layer growing on the original MAO coating can hinder the penetration of chloride ions and effectively adsorb a large number of NO3-to exchange Cl-in corrosion solution.