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

Jintao Niu,Zhanqiang Liu,Guijie Wang

doi:10.1109/access.2019.2941746

Jintao Niu, Zhanqiang Liu + Show 1 more

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https://doi.org/10.1109/access.2019.2941746

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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.

Highlights

Compared to conventional aluminum alloys, the addition of lithium to form Al-Li alloys yields some favorable features including lower density, higher specific strength, and higher specific stiffness
Specimen M was treated as follows. (I) Up-milling operations were conducted on blocks of alloy 2A97 under dry machining conditions using the process parameters described in our previous work [19]. (II) Specimens with dimensions of 10 × 10 × 6 mm were cut from the milled block using electric discharge machining (EDM)
The feed marks induced by the face-milling operation appeared on M surface (Fig. 1a); while no obvious mark associated with a specific direction appeared on GP surface (Fig. 1b)

Summary

Introduction

Compared to conventional aluminum alloys, the addition of lithium to form Al-Li alloys yields some favorable features including lower density, higher specific strength, and higher specific stiffness. These advantages make Al-Li alloys promising materials for use in aerospace applications [1]. Numerous Al-Li alloys with certain grades have been successfully used in spacecraft and aircraft to improve flight capability and lower flight cost. Taking alloy AA2099 as an example, a weight saving of 14.7% was achieved when it was used in major structural parts of aircraft wings [2]. Al-Li alloys are materials with great application potential, which means that they deserve thorough investigation

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