Characterization of adhesively bonded high strength steel surfaces treated with grit blasting and self-indicating pretreatment (SIP) adhesion mediator

Abstract

Abstract This work aimed at investigating the adhesion behavior of high strength steels (dual phase steel of grade DP 600 and microalloyed steel of grade ZStE340) which were glued with epoxy and polyurethane adhesives. To improve the adhesion strength of the steel surfaces, the surfaces were treated with three different methods: grit blasting with corundum or duroplast, self-indicating pretreatment (SIP) adhesion mediator, or a combination of grit blasting and SIP. The samples were aged in hot climate for 25 days. SEM investigations showed that the surface roughness values were significantly increased after grit blasting. Using EDX analysis, the surface of DP 600 steel after grit blasting indicated that the zinc concentration on the surface was clearly decreased, obviously in case of duroplast blasting. Whereas, the surface of ZStE340 steel after grit blasting showed that the carbon concentration was decreased. Adhesion strength of the samples in their fresh condition is dependent on adhesive type, steel grade and pretreatment method. SIP treatment was found to have a positive impact on the adhesion strength of the DP 600 steel regardless the type of adhesive. The effect of grit blasting on adhesion strength was more pronounced in case of ZStE340 steel. Generally, the adhesion strength of the aged DP 600 or ZStE340 samples was slightly decreased, with some exceptions confined to ZStE340 glued with EP 3 which showed an increase in the aging strength. The fracture surfaces of all samples were also examined in this work by naked eye and SEM.