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Hydrogen diffusivity and trapping have been studied in two advanced high strength steel grades and model samples using electrochemical permeation test. Microstructures of CP1000 and DP1000 steels consist of ferrite, martensite and a small fraction of retained austenite. In addition, bainite is present in CP1000. Model phases with predominance of a particular phase have been prepared by specific heat treatment. DP1000 has shown the lowest diffusivity among all materials, while ferritic model sample has shown the highest. Differences in hydrogen diffusion coefficient values are linked to trapping microstructural characteristics and grain size. [ABSTRACT FROM AUTHOR]

Inorganic fillers incorporated in adhesives for the automotive industry enable both functional and mechanical tuning of adhesive properties. While integral effects of additives are well understood, the individual effects of single components and how they may lead to synergies as well as antagonistic effects remain unclear. Here, we systematically vary the concentration of CaO, CaCO 3 and hydrophobic fumed SiO 2 to understand individual and combined effects. For this purpose, the inorganic additives were mixed into a model formulation without inorganic additives and compared with a close to real application one-component epoxy adhesive, which also contained these fillers. The water uptake of the filled adhesives was measured with EIS and the results were compared with findings from cataplasma tests under atmospheric conditions. These results indicated that hydrophobic SiO 2 can result in accelerated water uptake, although the opposite would be expected due to the more hydrophobic surface coating. In addition, blistering was observed on all galvanized steel (ZE) surfaces, while filiform corrosion was observed on all hot-dip galvanized Zn-Al-Mg steels (ZM). Cataplasma tests in oxygen-depleted and oxygen-rich atmospheres allowed to identify interfacial delamination processes. Our results showed that CaO can cause osmotic blistering and accelerate the diffusion of water into the adhesive due to a local increase in pH near the hydrated CaO particles, while CaCO 3 reduces water diffusion. However, coating defects may occur due to the addition of CaCO 3 , leading to increased cathodic blistering. A strategy for improving beneficial and synergistic effects is discussed. • Variation of CaO, CaCO 3 and hydrophobic fumed SiO 2 in coating • Effects of inorganic additives on the delamination process • Addition of hydrophobic additives did not prevent water transport in adhesive • CaO caused osmotic blistering and accelerated the diffusion of water on ZE surfaces • No osmotic blistering on CaCO 3 filled coatings applied on ZE surfaces [ABSTRACT FROM AUTHOR]

Water-uptake in hollow glass microspheres (HGM) filled polymers, and in turn corrosion processes along the polymer/metal-interface are not well studied to date. Here, we examine water absorption and diffusion of two epoxy adhesives in the absence and presence of HGM on zinc coated steel using electrochemical impedance spectroscopy and height-regulated scanning Kelvin probe. Mild filiform corrosion was detected on all epoxy adhesive coated Zn-Al-Mg (ZM) surfaces during Cataplasma aging, suggesting anodic delamination as degradation mechanism. In contrast substantial cathodic delamination and blistering was observed for epoxy/electrogalvanized steel samples (ZE). Hence, HGM containing coatings can inverse effects on ZM or ZE coated steel, having important implications for industrial application. • Water-uptake in hollow glass microspheres. • Corrosion resistance of hollow glass microspheres filled polymer coatings. • Water absorption behavior of real adhesive systems. • Cathodic and anodic delamination, scanning Kelvin probe. • Comparison model formulation and commercial epoxy adhesive. [ABSTRACT FROM AUTHOR]