Influence Of Metal Surface Pretreatments On Coating Adhesion

Coating technology is widely applied in surface modification, anti-fouling, anti-corrosion, anti-friction, high temperature resistance, insulation and so on. However, the weak binding strength of the coating with substrate limits the development of coating technology.This dissertation mainly focuses on the surface pretreatment. Copper substrate is pretreated with polishing, oxide etching, sandblasting and composite sandblasting. The PFA coating is then prepared on the pretreated copper substrate. And the effect of the pretreatment methods on the structure of the substrate and PFA coating is tested experimentally. The influence of the pretreatment methods on the anti-corrosion of coating and the binding strength between PFA coating and substrate is also characterized. The results indicate that comparing with polishing and oxide etching, sandblasting can increase the roughness of the substrate significantly, and the average roughness of the copper substrate can approach7.92μm. However, the roughness of the copper substrate sandblasted with178μm sand is too large and the rough structures are non-uniform. The shear strength of the coating prepared on the copper substrate sandblasted with178μm sand is about4.9MPa which is lower than that of the coating sandblasted with47μm sand. The non-uniform rough structure of the copper substrate pretreated by sandblasting with178μm sand can induce the stress cracking. Therefore, the anti-corrosion of the coating prepared on the pretreated copper substrate decreases significantly. Comparing with the PFA coating prepared on the copper substrate without sandblasting, the corrosion current density of the PFA coating prepared on the sandblasting pretreated copper substrate can decrease2orders of magnitude. The appropriate roughness and uniform rough structure on the copper substrate can be obtained by successively sandblasting with178μm and47μm sand. The shear strength of the PFA coating prepared on the pretreated copper substrate by composite sandblasting can approach13.5MPa and the hole sealing property becomes much better. Therefore, the anti-corrosion of the PFA coating prepared on the pretreated copper substrate is improved; the corrosion current density is4orders of magnitude less than that of the coating on the non-pretreated copper substrate. The results indicate that comparing with other pretreatment methods, the composite sandblasting pretreatment method has advantage on the anti-corrosion and protective life.The influence of composite sandblasting pretreatment on the adhesive strength and anti-corrosion of different substrate-coating systems is studied experimentally. Several substrates such as copper, Q235-C steel and aluminum brass are applied in the experiments. The influence of the roughness and the rough structure distribution on the anti-corrosion and adhesive properties of the coating is similar for the different substrate-coating systems. The anti-corrosion and adhesive strength can be improved by composite sandblasting pretreatment. However, the anti-corrosion and adhesive strength of the coating on Q235-C steel pretreated by sandblasting with178μm sand are improved insignificantly because the roughness induced by sandblasting with178μm sand is too small and the average roughness is only about3.37μm on the Q235-C steel due to its much larger hardness.