Pretreatments to Improve the Bondability of Hot Dipped Galvanised Mild Steel

It is well-established that some degree of surface pretreatment is vitally important in providing optimised adhesive bonds with metallic adherends. To date, much work has been carried out to determine the effectiveness of different pretreatments with aluminium, titanium and mild steel adherends, however, hot dipped galvanised (HDG) mild steel has received relatively little attention. In the present study, a range of pretreatments has been considered in terms of how they modify the HDG surface and how they perform in providing initial joint strengths and long-term durability. The chemical changes have been studied using Auger electron spectroscopy whilst the topography has been monitored using electron microscopy. The single lap shear joint (SLS) configuration was used to assess initial joint strengths and stressed SLS joints were exposed by complete immersion in deionised water with times-to-failure recorded as the measure of durability. A novel CO 2 -laser based cleaning process has been used for comparative purposes alongside the more conventional wet chemical pretreatments.