Improvement of Adhesion of High-Strength Steel Sheets by Surface Pretreatment with Dry Ice Blasting and Self-Indicating Pretreatment (SIP*) Adhesion Mediators

Abstract

Adhesive bonding of high-strength steel using epoxy (EP) and polyurethane (PU) adhesives was investigated. The steel surfaces were activated with dry ice blasting (DIB), and Self-Indicating Pretreatment (SIP)* coating was applied to improve the adhesion. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyses, and roughness measurements were carried out in addition to adhesive strength measurements. Our investigations indicate that adhesive strength improvement depends strongly on surface pretreatment, adhesive, and steel type. DIB improves the adhesion markedly. The combination of DIB plus SIP coating and EP adhesive increases the adhesive strength. The combination of DIB plus SIP coating and PU adhesive decreases the strength significantly. The increase in adhesive strength after DIB is due to the removal of contamination and lubricant layers. A further increase in adhesive strength after DIB + SIP coating by EP adhesive is due to the use of SIP coating, which acts as a coupling agent between the adhesive and the steel surfaces. The significant decrease in adhesive strength with PU adhesive after DIB + SIP coating is due to the increased size and number of closed bubbles in the adhesive layer, which act as stress raisers. DIB causes no changes in either topographic structure or surface roughness. EDX analysis of the treated surfaces indicates a reduction in carbon content and an increase in iron concentration.