Electrochemical investigation on the resistance of batch hot-dip galvanized coatings using a gel-type electrolyte

Abstract The efficacy of hot-dip galvanizing coatings in safeguarding steel components against corrosion largely hinges on the formation of a stable layer of corrosion products atop the coating. However, precise quantification of the resistance of this natural passive layer and the impact of climatic factors on its formation kinetics remain insufficiently understood. In a series of tests, the initial formation of the passive layer on zinc coatings conforming to DIN EN ISO 1461 under atmospheric weathering conditions using an electrochemical test method with gel electrolytes was examined. To this end, test specimens underwent galvanization in two different variants and were subjected to outdoor weathering for four weeks during both summer and winter. Electrochemical measurements conducted during this period yielded consistent and reproducible results for zinc coatings featuring an external pure zinc phase. The polarization resistance exhibited gradual development in several stages contingent upon the prevailing climatic conditions. Additionally, microscopic and macroscopic analyses indicated that the crystalline structure of galvanizing coatings, characterized by distinct zinc spangles, influenced the local properties of the surface layer. Conversely, samples with zinc coatings featuring continuous zinc-iron phases did not yield interpretable results using the gel-based measurement approach.