Effect of KH560 treatment on corrosion resistance of Al-Al2O3-silane composite coating

The 45 steel was sealing treated for various time in 6% (volume fraction) KH560 solution after the hot-dip aluminizing-anode oxidation. An Al-Al2O3-silane composite coating was formed on the surface of the 45 steel. The microstructure of composite coating was studied. The corrosion resistance of composite coating and its effect on the galvanic corrosion between the 45 steel and 30% (mass fraction) C-r/nylon6 composite were investigated. The results show that the silane coating effectively seals the cracks in Al2O3 coating, prevents the corrosive liquid from attacking the substrate. Hence, the corrosion resistance of the 45 steel is improved. Meanwhile, the good insulation property of the Al-Al2O3-silane composite coating can reduce the driving force of the galvanic corrosion between the 45 steel and 30% C-r/nylon6 composite, consequently, the galvanic corrosion resistance of 45 steel also is improved. After treated with the optimal KH560 treatment process for 5 min, the self-corrosion current density of the hot-dip aluminized 45 steel decreases by 3 orders of magnitude compared with that of the single hot-dip aluminized sample while the electrochemical impedance increases by 2 orders of magnitude, and the galvanic corrosion current density between the 45 steel and 30%C-r/nylon6 composite decreases by about 75%.