Corrosion resistance of the anodization/glycidoxypropyltrimethoxysilane composite coating on 6061 aluminum alloy

An anodization/gamma-glycidoxypropyltrimethoxysilane (GPTMS) composite coating was prepared via anodization, followed by a siloxane sealing treatment with and without pre-sealing to improve the corrosion resistance of the 6061 Al alloy. Hot water sealing (HWS) was used as for pre-sealing, while the spinning and dipping methods for siloxane sealing treatment were compared. The morphology, structure, and chemical composition of the coatings with and without sealing were characterized by FE-SEM, EDS, FTIR, and XRD. It was found that the porous anodic film was completely sealed in the double-sealed samples, including the AHD (anodized/hot water presealed/GPTMS sealed by the dipping process) and AHS (anodized/hot water pre-sealed/GPTMS sealed by the spinning process) coatings. In addition, the corrosion resistances of the coatings were evaluated using a potentiodynamic polarization test and salt spray test. The results indicated that the siloxane-sealed samples had significantly higher corrosion resistance than the hot water-sealed sample. The AHD and AHS coatings exhibited excellent corrosion resistance with absence of pitting corrosion after 336 h salt spray test. Moreover, scratch tests were carried out to measure the adhesion strength of the coatings, and the results revealed that the AHS coating had excellent adhesion strength. The effect of pre-sealing treatment on the anodized sample was also discussed.