The role of bending radius and coating/sheet thickness on corrosion protection capability of inorganic coatings on steel sheets

摘要

Metallic coated steel sheets used for example in building and construction applications are often ofsubject to forming operations such as cutting, pressing, bending, welding, hole-punching, etc. Eventhough the coatings are developed with the intention of being formed, care must be taken topreserve the strength of the steel as well as the corrosion protective properties of the coating.Bending is often considered as the most challenging forming operation and determines the steelgrade to be selected as well as the thickness of the coating and steel. The corrosion protectioncapability of a coating is often evaluated for non-formed, unaffected coatings. The effects offorming operations, such as bending, on the corrosion protection is invaluable information forconstructors.In this study, the role of bending radius on the corrosion protection capability have beeninvestigated for three commonly used types of inorganic coatings on steel sheets (hot dipgalvanized – HDG, aluzink – AZ, and zinc/aluminium/magnesium – ZM). Panels of the coatedsteel sheets were subjected to flap bending of two different bending radii (90° and 180° folds) andsubjected to an accelerated corrosion test (ISO 11997-1, cycle B)[1]. The areas in close vicinity(within 10 mm) of the bend, and most likely affected by the bending, were subject to weekly visualinspections with focus on base metal corrosion to evaluate the corrosion protection capability. Tostudy any peeling, tears or cracks of the coatings, cross-sections of the panels were studied usingscanning electron microscopy (SEM). Varying thicknesses of the coatings relative to the steelthicknesses were included in the study. The results of the accelerated test will be compared toresults from field testing on a site on the west coast of Sweden. Assessment of field test resultswill be performed during 2019-2021. The results from this study will be of interest when designingtests for assessment of corrosion protection capability of inorganic coatings on carbon steel sheet.