EXCIMER-LASER SURFACE MODIFICATION OF COATED STEEL FOR ENHANCEMENT OFADHESIVE BONDING

Zinc coated sheet steel in the form of temper rolled galvanize and gal vanneal are used extensively in the automotive industry. Through a pro cess of excimer laser surface treatment, we have developed a procedure to significantly enhance the adhesion characteristics of these coated steels. We report here results of processing trials using both XeCl ( 308 nm) and KrF (248 nm) excimer lasers and a two-part epoxy adhesive (3M DP-460) with a range of processing conditions, Bond strengths are measured by T-peel and shear test methods. Using T-peel tests, bond st rength improvements greater than five times than for untreated surface s have been observed. With the improved surface condition, the bond st rength becomes limited by the cohesive strength of the adhesive. Detai led measurements of the physical structure and chemical composition of the excimer laser processed surfaces are presented. The enhancement i n bond strength is correlated with the observed changes in physical an d chemical structure of the laser processed surfaces, Surface structur e is observed using SEM and physical characteristics are quantified us ing a Talysurf profilometer. The chemical composition of the treated s urface has been analysed using XPS and time-of-flight mass spectroscop y. (C) 1998 Elsevier Science B.V.