Comparative Study on Electrochemical Behavior of Al-Li Alloy 2A97 Machined Surfaces in Sodium Chloride Solution

Abstract

Al-Li alloys with the lower density and acceptable mechanical properties relative to conventional aluminum alloys possess great application potential in the aerospace field. Their anticorrosion behaviors attract research and industrial interests due to the incorporation of lithium element. In this study, Al-Li alloy 2A97 was subjected to face-milling and grinding-polishing operations. The face-milled and ground-polished surfaces were characterized by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The observations, including the brighter corroded surface, the higher impedance, lower corrosion current density, and nobler corrosion potential, suggested the superior corrosion resistance of the face-milled surfaces. The superiority in the corrosion resistance was attributed to the surface work hardening induced by the milling process. According to the variation trend of current density, the anodic branches of the polarization curves of the specimens were divided into three phases: preferential dissolution, protection enhancement, and breakdown. The three phases were identified by assuming that the protective effectiveness provided by the film on the alloy surface was proportional to its equivalent thickness. The small potential window of the passivation region indicated that the anodic protection method was unsuitable to protect alloy 2A97 in chloride-containing media.

Keywords

• Al-Li alloy
• corrosion products
• electrochemical behavior
• protective effectiveness
• protective film