| Micro-arc oxidation is an effective way which can improve corrosion resistance and wear resistance of magnesium alloy, bonding technology can avoid potential corrosion in joining of magnesium alloy which happen in riveting, welding and threaded joining owing to damage of coating on the surface. The surface state of micro-arc oxidation coating is an important factor which affects bonding strength of coating/adhesive. The adhesive property of micro-arc oxidation coating was researched in the article, and the effects of current density, frequency, duty cycle and oxidation time on bonding strength of the coating/adhesive were studied. Lap shearing test was employed to determine the bonding strength of the coating/adhesive. Contact angle and functional groups of adhesive were respectively measured by contact angel & surface tension analyzer and fourier transform infrared spectrometer (FT-IR). Roughness, surface morphologies of coating before and after shearing test, cross-section morphology of specimens and chemical bonding in adhesive interface were investigated respectively by roughness tester, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS).The results indicate that mechanical bonding force is an important component of adhesive force between coating and adhesive, which includes friction force result from roughness and interlocking force in the interface of coating/adhesive. Bonding strength of coating/adhesive is related to surface micromorphology of ceramic coating, as roughness of coating and pores' diameter increase, the adhesive in the pores increase, friction force and interlocking improve, result in enhancing of bonding strength. Bonding strength of coating/adhesive is influenced in various degrees by micro-arc oxidation technological parameters. When other technological parameters stay the same, bonding strength is enhanced along with increasing current density, decreasing duty cycle and time lasting, and the effect of frequency is not evident. However, the variation trend of bonding strength with technological parameters becomes gentle while roughness of coating and pores'diameter exceed a certain extent (roughness,0.5～0.8μm; pores' diameter,4～5μm). In this study, bonding strength of specimen treated by micro-arc oxidation is more superior than grinding, molybdate conversion and anodic oxidation, because of firm bond between coating and metallic matrix, the surface with roughness and porous structure is benefit for infiltration of adhesive, which form good adhesive-bonded joint. The failure mode of spesimen is complicated mixed mode fracture. |
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