Effect of Metallic Coatings on Hydrogen Embrittlement and Corrosion Performance of High Strength Wires

AbstractAn evaluation has been made of the relative efficiency of three hot-dipped metallic coatings, zinc (galvanising), aluminium, and a Zn–22Al–lMg alloy, as protection for drawn steel wires in chloride environments. The tests included corrosion tests with and without applied stress in neutral salt spray and in acidified salt spray contaminated with sulphide, and electrochemical measurements. It was found that in oxygenated chloride atmospheres, aluminium coatings gave more protection than zinc, but zinc was superior in conditions of oxygen starvation. In neutral chloride zinc and aluminium were equally protective against stress corrosion, but in sour chloride, aluminium was much superior to zinc, and the alloy superior to both. On stressed bare wires, it was found that the time to failure in sulphide-containing environments decreased with increase in the applied current density, this leading to greater hydrogen embrittlement.