Stress corrosion behavior of 6082 aluminum alloy

Abstract

Stress corrosion tests of 6082 aluminum alloy were carried out by using a three‐point bending fixture while holding at 50% of yield strength state through different immersion times in 1.5% NaCl electrolyte solution. The electrochemical impedance spectra and dynamic electric potential polarization curves were measured to indicate the stress corrosion behavior of the alloy. Optical microscopy, scanning electron microscopy, and X‐ray energy spectrum analysis were applied for microstructural investigations. The results show that all of the Nyquist electrochemical impedance spectra consisted of high‐ and low‐frequency double capacitive arcs. However, an increase in immersion time while holding at 50% of yield stress resulted in a corresponding increase in the corrosion current density, leading to gradual corrosion depth growth, and a decrease in the corrosion resistance of the alloy. 6082 Aluminum alloy included AlMnFeSi, Mg2Si, and Si secondary phases. The different secondary phases presented different stress corrosion behaviors. Stress corrosion cracks were generated at the boundaries of AlMnFeSi and matrix or within the AlMnFeSi phase. Crack direction is always perpendicular to the tensile stress applied. Mg2Si secondary phase was self‐corroded as its corrosion potential is lower than that of the matrix. As the electric potential of Si is higher than that of the matrix, corrosion occurred at the matrix side of the boundary between Si and matrix.

Effects of environmental factors on corrosion behavior of aluminum

“…As mentioned before, the chloride ion is the major cause of pitting corrosion, [19] and it appears to be adsorbed to the surface by the external environment. Furthermore, sulfur is also suspected to have deleterious effects on the corrosion behavior of Al, and it may flow from the soil.…”

“…Chlorine ions are known as a major element causing pitting corrosion by chemical attack of the passive film on the aluminum surface. [18][19][20][21] Particularly, corrosion of aluminum may be further promoted in summer due to the hot and humid environment. [22] Also, Cl − ions on the surface of the heat exchanger may be concentrated, leading to a serious corrosion phenomenon.…”

Atmospheric corrosion behavior of 7A09 aluminum alloy exposed to an industrial environment

“…Specimens for this study were the 7A09-T6 aluminum alloys with the following chemical composition (wt%): 0.45 Fe, 0.23 Cr, 1.49 Cu, 0.06 Si, 2.80 Mg, 5.80 Zn, 0.02 Ti, and balance of Al. The plate samples used for exposure tests had a size of 100 × 50 × 3 mm 3 . Before the tests, all the samples were ground down to 2000# with silicon carbide abrasive papers, cleaned ultrasonically in acetone, rinsed with alcohol, and then weighed with a precision of 0.0001 mg.…”

“…High-strength aluminum alloys of 7XXX series have high-strength/density ratio, toughness, as well as good processing properties, which make them attractive for applications in aviation and aerospace. [1][2][3] However, the high corrosion susceptibility of this series of alloys is a critical factor that affects their application, and the corrosion attacks of which have been found in main forms of pitting, intergranular corrosion (IGC), exfoliation corrosion, and even stress corrosion cracking when the alloys were exposed to the atmospheres. [4,5] The atmospheric corrosion of aluminum alloys is a result of chemical/electrochemical reaction in a thin electrolyte layer, which is related to the synthetic effects of multiple environmental factors, such as air temperature, relative humidity, sunshine, pollutants, and wind.…”

“…High‐strength aluminum alloys of 7XXX series have high‐strength/density ratio, toughness, as well as good processing properties, which make them attractive for applications in aviation and aerospace. [ 1–3 ] However, the high corrosion susceptibility of this series of alloys is a critical factor that affects their application, and the corrosion attacks of which have been found in main forms of pitting, intergranular corrosion (IGC), exfoliation corrosion, and even stress corrosion cracking when the alloys were exposed to the atmospheres. [ 4,5 ]…”