Electrochemical properties and nano-hardness of anodic oxide film grown over Al-Cu alloy

Abstract

Al-Cu alloy is largely employed in mechanical and aircraft industries. Usually aluminum and aluminum alloys are submitted to an electrochemical process called anodizing that consists on growing an oxide film on their surface. The oxide film protects metallic substrate because it has higher hardness and corrosion resistance, but in the case of alloys the anodizing process using direct current becomes difficult due to the presence of alloying elements. The aim of the present work was to develop a procedure to anodize Al-Cu alloy using pulsed current. The electrochemical properties were analyzed by electrochemical impedance spectroscopy (EIS) in a 0.5 M NaCl solution. Information about the structure of the formed anodic oxide was obtained using an equivalent circuit described in literature and Boukamp fitting procedure. Interpretation of EIS results showed that films grown using pulsed current, when compared to similar oxide films produced using direct current, have better corrosion protective properties. The superior properties of the samples prepared by pulsed current were also observed through their hardness results. Such data were obtained by nanoindentation technique, in a Hysitron Triboindenter system. This equipment allows determination of mechanical and tribological properties of materials in the nanoscale range.