Improvement of galvanized high-strength steel surface condition by hot water treatment for metal-plastic hybrid joining

Abstract

Recently, metal-plastic hybrid joining technology is becoming very attractive in the automotive industry because it contributes to structural light-weighting and decarbonization of society. For metals and plastics with obviously different properties, it is necessary to perform surface pretreatment to promote hybrid joining. Galvanized high-strength steel (GHSS) has been widely used in the car body because of its excellent anti-corrosion properties and mechanical performance. Hot water treatment (HWT) is a simple and eco-friendly process in which metal substrates are immersed in hot deionized (DI) water, generating nanostructures and changing the chemical condition of the metal surface through oxidation and 'plugging' mechanisms.In this study, the effects of HWT at different pH and temperatures on the GHSS surface condition were explored. Zinc oxides and hydroxides with different amounts were generated on the surface to promote surface anchoring effects and hydrogen bonding. In conclusion, the anchoring effect produced by the oxide needle-like structures is considered to be a major factor in promoting joining. High-ph environments were found to inhibit the full growth of oxide needle-like structures. The presence of hydroxide had the potential to promote hydrogen bonding, but defects induced by its dehydration decomposition were found to be one of the unfavorable factors.