Electrochemical Polishing of 7075 Al Alloy in Phosphoric Acid

7075 aluminum (Al) alloy has been widely used in aircraft structures and other high-end electronic products owing to its excellent mechanical and chemical properties, while its damage-free and highly efficient surface finishing remains a challenge. Herein, we demonstrate a systematic study of the anodic behaviors of 7075 Al alloy during the electrochemical polishing (ECP) process in phosphoric acid under different applied potentials, and the changes of surface morphology, roughness, electric current, and resistance are studied intensively. According to the surface morphology and current density, the ECP of 7075 Al alloy can be divided into 4 stages including the negative leveling stage, leveling and corrosion stage, leveling and brightening stage, and pitting and corrosion stage. Different factors influencing each stage and the effects of impurity phases in the ECP process are experimentally validated. Under optimized conditions, a mirror surface with a roughness (Ra) of 46.7 nm (decreased from an initial value of 153.2 nm) can be obtained by ECP for 10 min. The presented findings are of great value for the further development of ECP process of multiphase alloys.