Effect of moisture content in uncured adhesive on static strength of bonded galvanized DP600 steel joints

Experiments to characterize the effect of moisture content in uncured adhesive on static strength of bonded galvanized DP600 steel joints were conducted. Prior to adhesive curing, the adhesive and galvanized steel coupons were pre-exposed to 96% relative humidity at 40 °C (i.e., open-faced exposure). It was found that the exposure of adhesive and steel sheets in hot humid environment decreases the quasi-static strength of adhesive-bonded galvanized DP600 steel joints by as much as 96% after 1008 h of exposure. Optical microscopy and scanning electron microscopy of quasi-static tensile tested specimens and moisture absorption testing of bulk adhesive revealed that static strength degradation is mainly due to the plasticization and micro-cracking of adhesive and zinc oxidation by the water vapor.