水热预处理对铝合金表面ZnAl-LDHs涂层防腐蚀性能的影响

目的提高表面ZnAl-LDHs涂层对铝合金的防腐蚀保护性能。方法首先将6061铝合金放入水热反应釜中,加入去离子水,在120℃温度下水热反应30 min。将经过水热预处理的铝合金分别放入50、80℃的0.005 mol/L的Zn(NO3)2溶液中浸泡4 h,在铝合金表面制备出ZnAl-LDHs涂层。利用XRD、SEM、EDS、EIS和极化曲线等技术,分析不同制备条件下,铝合金表面ZnAl-LDHs层的形貌、结构及其对铝合金的防腐蚀保护性能。结果水热预处理后,铝合金表面形成Al(OH)3和AlO(OH)混合层,在其上生长形成的ZnAl-LDHs涂层具有较优的层状结构、较高的结晶度和更加细小致密的纳米片。电化学阻抗和极化曲线的测试结果表明,表面ZnAl-LDHs层可以降低6061铝合金的腐蚀电流密度,提高腐蚀电位和电化学阻抗。水热预处理后的铝合金在80℃溶液中形成的ZnAl-LDHs层,其自腐蚀电流密度(J(corr))仅有0.018μA/cm^2,比未水热处理的铝合金上获得的ZnAl-LDHs层(0.101μA/cm^2)更低,在50℃溶液中形成的ZnAl-LDHs层也观察到相同的现象。结论通过水热预处理可在6061铝合金表面形成Al(OH)3和AlO(OH)混合层,将其作为ZnAl-LDHs层原位生长的前驱体,可以促进ZnAl-LDHs的结晶形核,提高其形核率,使ZnAl-LDHs层的纳米片更细小致密,从而使ZnAl-LDHs层对铝合金具有更好的防腐蚀保护性能。

Effect of Hydrothermal Pre-treatment on Anti-corrosion Properties of ZnAl-LDHs Prepared on the Surface of Aluminium Alloys

The work aims to improve the corrosion resistance of ZnAl-LDHs on the surface of aluminum alloys.Firstly,the 6061 aluminum alloy was placed in the hydrothermal reactor and hydrothermal treatment was conducted with deionized waterfor 30 minutes at 120 ℃. Secondly, the aluminum alloy after hydrothermal treatment was respectively immersed in 50 ℃ and80 ℃ 0.005 mol/L Zn(NO3)2 solution for 4 hours to prepare ZnAl-LDHs coatings. The surface morphology, structure andcorrosion resistance of the ZnAl-LDHs coatings prepared in different conditions were analyzed by XRD, SEM, EDS, EIS andpolarization curve method, respectively. After hydrothermal treatment, the mixed layer of Al(OH)3 and AlO(OH) was formed onthe aluminum alloy and the ZnAl-LDHs coating on such layer had better lamellar structure, higher crystallinity and finer anddenser nanosheets. The results of EIS and polarization curve showed that the ZnAl-LDHs coating prepared on the surface of6061aluminum alloy could reduce the corrosion current density and enhance the corrosion potential. After hydrothermaltreatment, ZnAl-LDHs coating was formed on aluminum alloy surface in 80 ℃ solution and the self-corrosion current densitywas only 0.018 μA/cm2, five times lower than that of ZnAl-LDHs (0.101 μA/cm2) prepared on the surface without hydrothermaltreatment. The same condition was also observed on the ZnAl-LDHs coating formed in 50 ℃ solution. A mixed layer ofAl(OH)3 and AlO(OH) can be formed on 6061 aluminum surface after hydrothermal treatment and can be used as a precursorfor in situ growth of ZnAl-LDHs to promote the crystallization and nucleation of LDHs, reduce the size of coating nanosheetsand improve corrosion resistance of ZnAl-LDHs coatings on aluminum alloy.