The Effect Of Surface Pretreatment On Galvanic Corrosion Resistance Between The 45# Steel And 30% C_f/Nylon6 Composite

Carbon fiber reinforced composite is being increasingly applied to automotive industry due to its good combination of low density,thermal stability and good mechanical property.However,as a conductive material with high polarization potential,carbon fiber is prone to galvanic corrosion with metal when it is in contact with metal in use because of high potential difference between them.As a part of the GM United Fund Project“Study on Galvanic Corrosion Behavior of Dissimaliar materias of 30%C_f/PA6 Composites”,which carried out by General Motors Corporation（GM）and Zhengzhou University,this study fouses on the improvement effect of Al₂O₃ coating and silane coating on the corrosion resistance of the 45#steels and their influence on the galvanic corrosion resistance between 45#steel and 30%C_f/PA6 composite.Hot dip aluminized 45#steels（HDA 45#steel）were coated with anodic oxidation（HDA-AO 45#steel）and silane sealing（HDA-AO-SS 45#steel）processes.Various thicknesses of Al₂O₃ coating and Al₂O₃-silane composite coating coated on the surface of HDA-AO 45#steel and HDA-AO-SS 45#steel.The morphology,thickness and chemical composition of two kinds of coatings were studied by scanning electron microscopy（SEM）,XRD and XPS analyses technologies.The corrosion resistance of coated HDA-45#steels and the galvanic corrosion resistance of between the coated HDA-45#steel and 30%C_f/PA6 composite were studied by potential dynamic polarization test,EIS test,galvanic current density test and full immersion test.The main research achievements are as follows:Compared with the HDA-45#steel,the Al₂O₃ coating coated on the surface of the HDA 45#steel after the anodic oxidation obviously improved the corrosion resistance of the HDA-45#steel and the galvanic corrosion resistance between the HDA 45#steel and the 30%C_f/PA6 composite.But the the internal defects of Al₂O₃ coating weaken their improvement.The HDA-AO 45#steel with 12.62μm thickness of the Al₂O₃coating has the best corrosion resistance and galvanic corrosion resistance compared others.Compared the HDA 45#steel,the self-corrosion current density of HDA-AO45#steel decreased by 1-2 orders of magnitude,the electrochemical impedance increased by 1 order of magnitude while.the galvanic corrosion current density of between the 45#steel and the 30%C_f/PA6 composite decreased by about 53%.Silane sealing treatment further improved the corrosion resistance of the HDA-AO 45#steels and their galvanic corrosion resistance with 30%C_f/PA6 composite.The HDA-AO-SS 45#steel with 12.62μm thickness of the Al₂O₃ coating and 9.7μm thickness of the silane coating has the best corrosion resistance and galvanic corrosion resistance.After Silane sealing,the self-corrosion current density and the electrochemical impedance of the HDA-OA-SS 45#steel decreased by 2 orders of magnitude and increased by 3 orders of magnitude respectively compared with that of the HDA 45#steel.The galvanic corrosion current density of between the HDA-AO-SS 45#steel and the 30%C_f/Nylon 6 composite decreased by about 76% also.The improvement of anodic oxidation and silane sealing to the galvanic corrosion resistance of HDA 45#steel and their galvanic corrosion resistance with the30%C_f/Nylon 6 composite can be attributed to the Al₂O₃ coatings with higher polarization potential not only reduce the driving force of the galvanic corrosion between the HDA 45#steel with the 30%C_f/PA6 composite by decreasing the difference of their polarization potential,but also increase the charge transfer barrier and decrease the galvanic corrosion current density when the galvanic corrosion occurs.The silane coating on the surface of HDA-OA 45#steel effectively sealed the defects in the Al₂O₃ coating,which prevented the corrosive liquid through the defects in the Al₂O₃ coating to attack the 45#steel substrate.Furthermore,the good insulation property of the silane coating can further reduce the driving force of the galvanic corrosion between the HDA 45#steel with the 30%C_f/PA6 composite,and hence furher enhance the charge transfer barrier to be overcome by galvanic corrosion also.Service Environment has significant influence on the galvanic corrosion resistance of HDA-OA-SS 45#steel and 30%C_f/PA6 composites.Raising the temperature of corrosive solution increased significantly the current density of galvanic corrosion.Altough the current density of galvanic corrosion increaseed with the increase of the concentration of corrosive solution,their change is little when the concentration of corrosive solution is above 6%.The current density of galvanic corrosion first decreased then decreased with the increase of pH.Overall,the temperature of corrosive solution has the most significant effect on the the galvanic corrosion resistance of HDA-OA-SS 45#steel and 30%C_f/PA6 composites among all environmental factors.