Durability of Lap-Shear Adhesive Joints with Coated Steels in Corrosive Environments

Lap-shear strength degradation of epoxy bonded coated steels was studied with exposure to cyclic salt-spray and thermal environments. Joint strength degradation with cyclic salt-spray and humidity exposure is slow with coated steel adhereneds, e.g, hot-dip galvanized, electrogalvanized, galvannealed, and Zincrometal^®, and fast with bare steel adherends. Corrosion and dissolution of the steel coating, not adhesive degradation, is the primary mechanism leading to the loss of joint strength in this environment. With unexposed samples, joint strength is limited by either the mechanical strength of the sheet or the adhesion of the coating. The mill and drawing oils used had little effect on initial adhesive joint strength.