Embrittlement of Hot-Dip Galvanized Steel: A Review

Zinc coated steels are widely used in automotive and construction industries, due to their superior corrosion resistance compared to uncoated steels. Hot dip galvanizing is one of the most economically viable zinc coating techniques, developed over 200 years ago. However, modification in the zinc bath composition, more advanced structural designs, along with demanding service conditions have resulted in increased instances of failure of galvanized steels. Failure of galvanized steels can take place by several mechanisms such as liquid metal embrittlement (LME), hydrogen embrittlement (HE), distortion cracking and strain age embrittlement. For failure analysis to be carried out, it is important that the background and service history of any component is thoroughly understood. In this respect, the various mechanisms and the factors affecting them during and after galvanizing are discussed in this paper. The numerous factors are broadly categorized as (i) pre-treatment and galvanizing process, (ii) properties of the steel to be coated, (iii) properties of the galvanizing bath, (iv) galvanizing process parameters, (v) fabrication process and (v) service condition. Several experimental results and case studies are presented to understand the embrittlement and fracture of galvanized steels.