Chemically Induced Passivity of Aluminum Alloys and Al-Based Metal MatrixComposites

摘要

The concept of surface modification has been applied for corrosion protection ofcommercial aluminum alloys such as Al 2024, Al 6013, Al 6061 and Al 7075. The goal of this project was to develop methods of corrosion protection which do not use toxic chemicals. The Ce-Mo process consisting of immersion in hot solutions of CeC13 and Ce(N03)3 followed by anodic polarization in a molybdate solution has produced surfaces with exceptional resistance to localized corrosion for Al 6013 and 6061. Surface modified samples did not pit during exposure to 0.5 M NaCI for 30 day For Al 2024 and Al 7075 it was found that a copper removal pretreatment step was necessary for complete corrosion protection. For Al 2024 replacement of CeCl3 by Ce acetate produced optimum results. Surface analysis showed that both Ce and are incorporated in the modified surface layers. For Al 7075 it was found that increase concentrations of Ce and Mo occur at sites where Cu containing particles are located It is assumed that the exceptional corrosion resistance is in part due to eliminatic of local cathodes during the Ce-Mo process. Anodic polarization curves for Al 2024 and Al 7075 showed that the pitting potential Epit was increased after surface modification, while the corrosion potential E(corr) remained constant. Apparently the amount of adsorbed Cl(-) at a given potential is reduced in the presence of negatively charged Mo species in the modified surface layers.