The effects of an Fe–Zn intermetallic-containing coating on the stress corrosion cracking behavior of a hot-dip galvanized steel

This study deals with the mechanical behavior of galvanized, interstitial free (IF) steel in air and sodium chloride water. Tensile tests conducted in air at different strain rates lead in general to a ductile behavior. It can become brittle when tested in a NaCl solution at particular strain rate values. Fractographic analysis shows a brittle fracture similar to hydrogen embrittlement (HE). A detailed analysis taking into account both the individual mechanical strength of the phases on the coating as well as the electrochemical reaction between Zn and water allow the explanation of this embrittlement. Hydrogen can be produced and can penetrate the cracks formed inside the intermetallic phases of the coating during loading, thus, reaching the steel substrate. The HE of the IF steel, assisted by zinc dissolution and galvanized coating low toughness, appears to be the cause of the loss of ductility observed in the presence of specific environmental conditions, strain rates and morphologies of the coating.