Passivation behaviors of 6082 aluminium alloy under stress corrosion process

Abstract

We systematically studied the passivation process of 6082 aluminium alloy under the bending stress situation by combining electrochemical measurement techniques with three‐point bending stress fixture designed by our lab, and then examined the microstructures of corroded specimens to analyze electrochemical corrosion mechanism in 1.5% NaCl solution. The results show that secondary Mg2Si phase acts as the anodic electrode, leading to the self‐corrosion of Mg2Si phase. As a result, the spots of self‐corroded Mg2Si phase within grains act as initial pitting corrosion site, combined with tiny, massive precipitated Mg2Si particles at the grain boundaries and bending stress, leading to the failure of surface of the 6082 aluminium alloy. The corrosion current density increases from 3.422 × 10−7 to 13.77 × 10−7 A/cm2 when bending stress level was increased from 0% up to 100% of yield stress. Passive film formation process occurred between polarization potential area of −1.05 and −0.65 V. Sectional microstructural investigations show that the corrosion starts penetrating vertically into the material before it develops corrosion paths extending parallel to the surface, leading to massive stress‐induced corrosion cracks. The maximum corrosion depth increases from ∼24 μm on specimen without any stress applied to 85 μm when bending stress of 100% yield strength is applied.

Understanding Localized Corrosion on Metal Surfaces Using Scanning Electrochemical Cell Impedance Microscopy (SECCIM)

“…Pitting and galvanic corrosion are the most common types of corrosion mechanisms observed in lightweight multimaterial automotive structures. − Specifically, galvanic corrosion occurs when two dissimilar metals are joined and one corrodes preferentially, whereas pitting is localized corrosion that results in small pits on the metal surface . The mechanical, chemical, and physical properties of metal or metal alloy surfaces contribute to the origin of surface oxidation in the presence of oxidants (e.g., salt solutions and ions).…”

Corrosion and passivation behavior of 6082‐T6 aluminum alloy in NaCl solution

“…[10][11][12] The corrosion resistance of aluminum alloys depends on the formation of a layer of the protective passive film. [13][14][15] However, this passive film is vulnerable to attack in solutions containing chloride. It was reported [16][17][18][19] that chloride ions (Cl − ) are preferentially adsorbed around vulnerable defect sites such as intermetallic particles, inclusions, and mechanical damages, resulting in a weakening of the passive film.…”

Improving Discharge Voltage of Al-Air Batteries by Ga3+ Additives in NaCl-Based Electrolyte

“…Figure 9. Activation mechanism of Al in the 2 M NaCl electrolyte (a) without and with different contents of GaCl 3 additives: (b) 0.05 M, (c) 0.1 and 0.15 M, (d) 0.2 M.Since Al is easily oxidized, an oxide film forms on the surface, and the following reactions occur[48]:Al + 2H 2 O → AlOOH + 3H + + 3e −(9) in which the AlOOH is Al 2 O 3 •H 2 O. When Cl − exists, it competes with water molecules for adsorption on the surface of the oxide film.…”