Improvement in hot dip galvanized coating microstructure and properties by pre-metallic deposition on steel surface: A comprehensive review

The product and process of batch and continuous galvanizing have witnessed a paradigm shift in the last two decades. This is due to the need of high strength and advanced high strength steels as well as stringent requirements of surface quality, formability, and corrosion performance from the end customers. The major concerns in galvanizing research are, coating overgrowth for batch galvanizing leading to excess zinc consumption, and selective oxidation of alloying elements in high strength steels leading to bare spot defects for continuous galvanizing. Additionally, zinc coated steels, especially press hardenable steels (PHS) and advanced high strength steels (AHSS) suffers from liquid metal embrittlement during hot stamping and resistance spot welding processes. The application of pre-coating before galvanizing has gained importance in addressing such perennial industrial issues. Metallic pre-coatings e.g., iron, nickel, copper and/or their alloys e.g., NiP, CuSn etc. have been reported to produce defect-free galvanized coatings with superior properties. The present article presents a comprehensive, comparative, and critical overview of the research articles in this domain. The application of pre-coating and their effect on microstructural development and interface formation are dealt in this article. The effect of such pre-coatings on LME performance as well as corrosion performance is also discussed. Information relevant to filed patents, industrial practices and recent industrial adaptation is also outlined. Finally, the article puts forward prospective research opportunities in this domain.