Corrosion resistance of steel wires galvanized with Zn-Al Alloy

High strength bridge wires galvanized with zinc (Zn) and aluminium (Al) alloy is expected to have higher corrosion resistance than those galvanized with Zn. The steel wire with a diameter of 5mm galvanized with Zn (90%) and Al (10%) alloy is produced and corrosion acceleration tests have been conducted. The corrosion resistance is then compared with the steel wires galvanized with Zn. The steel wire specimens are kept under three different corrosion environments: kept at a relative humidity (RH) of 60%, kept at a RH of 100%, and wrapped with wet gauze which simulates the wet condition. The wire specimens are kept in the thermo-hygrostat at 40oC for five months. The mass loss due to corrosion under the relative humidity of 60% and 100% is much smaller than that under the wet environment, and the amount of corrosion isn’t much different between Zn-Al galvanized wires and Zn galvanized wires. On the other hand, the mass loss of the steel wires galvanized with Zn-Al is distinctively smaller than those galvanized with Zn under the wet condition. The mass loss of the NaCl attached wires is twice larger than that without NaCl under the wet condition. The corroded wires are investigated by an optical microscope showing that the corrosion product of the Zn layer is loose and easy to exfoliate from the steel layer. On the contrary, the corrosion product of the Zn-Al alloy layer is dense and hard to exfoliate from the steel layer. This difference is the reason of the superiority of the Zn-Al galvanized wires.