Volvo Laboratory Study of Zinc-Coated Steel Sheet-Adhesive Bonding Properties

The adhesive bonding properties of fourteen coatings were evaluated. Three different types of adhesives were tested: epoxide onecomponent (structural adhesive), PVC-plastisol (autiflutter and stiffening adhesive) and acryl-plastisol (weldbonding hemflange adhesive). Bonding was carried out on an oily steel surface. Curing was done on the production line. After different climate treatments, single lap shear specimens were tensile tested and failure mode was determined.

The values of shear strength do not indicate any dramatic change after the different aging treatments compared with unaged reference samples. However, somewhat lower strength is observed when samples are bonded with epoxide in combination with ZnNi and ZnFe coating.

Most bonds failed by cohesive failure, which is preferred. But some exceptions occurred. Epoxide bonds between zinc-iron or zinc-nickel coating failed by delamination of the metal coatings, and explains the somewhat lower strength. This type of failure is due to the brittleness of these coatings. PVC-plastisol bonds between zinc-iron or zinc-nickel show adhesive failures.

Thus, great care must be given when new zinc coatings are bonded together.