Corrosion resistance of model ultrafine-grained Al-Li alloys produced by severe plastic deformation

Abstract

The influence of grain boundaries and fine precipitation on the corrosion behavior was investigated in two model aluminum-lithium alloys, namely (in wt%) Al-1.6Li (lithium in a solid solution) and Al-2.3Li (lithium in the form of Al 3Li precipitation), subjected to three different severe plastic deformation (SPD) treatments which refined the microstructure of the alloys to the ultrafine grain size. The SPD techniques used in the experiments were equal channel angular pressing (ECAP), hydrostatic extrusion (HE), and extrusion-torsion (ET). The corrosion behavior was examined using a potentiodynamic polarization test, electrochemical impedance spectroscopy, and an immersion test followed by a SEM surface analysis. The electrochemical tests were conducted in a 0.1 M Na 2SO 4 solution added with 100 ppm of Cl -. The immersion tests (48 h) were performed in a 3.5% NaCl solution at room temperature. The results indicate that the pitting potential, pit number, and stability of the passive layer formed on the surface of the substrates undergo changes depending on the average grain size and the presence of precipitation or its lack. The corrosion resistance, examined in the solution mentioned above, appears to increase with decreasing average grain size. The ET method gave the microstructure with the lowest corrosion resistance. © 2011 The Author(s).