| dc.description.abstract | Hot-dip zinc、electroplating zinc and 55%Al-Zn coating were investigated for comparison of their corrosion resistance, electrochemical behavior in 3% NaCl of varying with pH value solution. The assessment corrosion and electrochemical phenomenon of coating zinc sheet steel were employed with immersed corrosion, opening circuit potential, Tafel polarization, cyclic polarization.
Compared with the OCP and weight loss, SGLC surface is covered by aluminum oxide layer which protects the function. The result is that its weight lost less and OCP towards to the noble potential. But in pH=11, this oxide layer is easier destroyed to cause the corrosion rate rise. However, the surface of SGCC and SECC is formed the oxide layer with unstable in acidic environment, and it is easy to decompose, to cause weight loss increase with the pH decreases and the OCP decrease with the pH decreases. But in the alkalinity environment is covered by the oxide layer which transformed from the degrees of Zinc hydroxide to protect coating.
From Tafel polarization, 3% NaCl of varying with pH value solution except pH=11, its corrosion resistant ability decreases for SECC＞SGLC＞SGCC. In pH=11, SGLC corrosion rate are enhanced in the short time. Therefore, the corrosion resistance which is under this environment decreases in order to SECC＞SGCC＞SGLC.
In cyclic polarization, SGLC only has the passive state characteristic appearance also presents by the negative hysteresis curve in pH=11. SGCC has obviously passive state characteristic, but its protected ability is not good enough. The result of the passive state area is unable to do the completely display, and to create the localized corrosion. SECC has entirely passive membrane, but it is easy to different pH value accessibly. Above of all will cause pitting formation which will also make the serious destruction to the substrate on. | en_US |