Abstract
The effect of the increase in crystalline defects in the structure generated by high-pressure torsion (HPT) on the corrosion behavior of metallic materials is not well understood. This report evaluates the influence of HPT on the corrosion behavior of a solution treated Al-3wt% Mg-0.2wt% Sc alloy in a 3.5 wt./v.% NaCl solution. The electrochemical behavior of the alloy was evaluated using cyclic polarization, electrochemical impedance spectroscopy (EIS), Mott Schottky, X-ray photoelectron spectroscopy, and chronoamperometry testing. The passive current density decreased after HPT processing, indicating a more protective oxide layer was formed on the surface of the HPT-processed alloy. Mott Schottky analysis confirmed the higher protection efficiency of the passive layer on the HPT-processed alloy. The film formed in the solution-treated alloy was a p-type and an n-type semiconductor while the alloy processed by HPT exhibited only an n-type semiconductor behavior. EIS showed that corrosion resistance in a saline medium increased with HPT processing.
Highlights
Aluminum alloys are used extensively in civil construction and the automotive and aerospace industries due to their high strength-to-weight ratio, recyclability and high thermal and electrical conductivity
Localized corrosion is usually initiated at the oxide layer at sites weakened by chloride attacks, chemical or physical heterogeneities at the surfaces may act as preferential nucleation sites[2]
It should be noted that the grain size after high-pressure torsion (HPT) processing agrees with previous reports for this alloy[14,20] and the grain structures appeared to be homogeneously distributed throughout the entire areas of the scanning electron microscope (SEM) images
Summary
Aluminum alloys are used extensively in civil construction and the automotive and aerospace industries due to their high strength-to-weight ratio, recyclability and high thermal and electrical conductivity. They have high corrosion resistance due to the development of protective oxide films on their surfaces when exposed at room temperature to environments containing oxygen[1]. Because of the intense straining and grain refinement, these materials generally exhibit increased mechanical strength, good ductility and high resistance against fatigue and wear at low temperatures, as well as excellent superplastic properties at high temperatures[5,6,7,8,9]. Amongst SPD techniques, high-pressure torsion (HPT)[10,11] permits the production of materials with finer grain structures and usually higher hardness through the application of high hydrostatic pressures together with torsional straining in disk-shaped samples
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