Evaluation of surface and bonding properties of cold rolled steel sheet pretreated by Ar/O2 atmospheric pressure plasma at room temperature

In this study, cold rolled steel sheet for automotive was pretreated by the Ar/O2 atmospheric pressure plasma at room temperature to improve the adhesive bonding properties. Through the analysis of contact angle and calculation of work of adhesion, the change of surface properties related to the plasma power, treatment time, and flow rate of O2 gas were investigated before and after plasma treatment. Contact angle was degreased and work of adhesion was increased after plasma treatment. Meanwhile, the changes of surface roughness and morphology were observed by atomic force microscopy (AFM). And the chemical compositions of the steel sheet before and after plasma treatment were characterized by X-ray photoelectron spectroscopy (XPS). Surface roughness was slightly changed and new functional group, oxides, appeared on the surface of steel sheet after plasma treatment. Based on design of experiments and artificial neural network (ANN), the single lap shear test was performed to analyze the effect of plasma treatment parameters gas on adhesive bonding strength. From the result of the single lap shear test, the adhesive bonding strength of joint which was treated by Ar/O2 atmospheric pressure plasma was improved about 23% compared with that of untreated sheet.