Surface & Coatings Technology 348 (2018), 121-129; https://doi.org/10.1016/j.surfcoat.2018.05.048

Abstract

The present work suggests a new approach of chromate-free surface pretreatment of aluminum alloy AA 1050 by using a modified phosphoric acid anodizing process, followed by an impregnation with a commercial SiO₂-nanoparticle dispersion (Levasil® 300/30%) by dip-coating technique. The nanoparticles constitute an additional barrier layer against corrosion without closing the pores completely. The open porous oxide layer is a suitable promoter of adhesive bonding. The influence of withdrawing speed, the dipping time, solid content, temperature and pH-value in respect to the filling height in the pores of the anodized oxide layer were investigated. Surface morphology of the impregnated anodic oxide layers as well as their cross-section microstructure were investigated by scanning electron microscopy (SEM). Corrosion properties were investigated by electrochemical impedance spectroscopy (EIS) and adhesion was evaluated by single lap shear tests.