Passivation behaviors of 6082 aluminium alloy under stress corrosion process

• Published in: Materials and corrosion Vol. 72; no. 3; pp. 564 - 574
• Main Authors: Zhou, Bin, Yang, Li, Yang, Shou‐bing, Zhang, Chi, Li, Yan‐zhou, Bai, Di, Huang, Gen‐zhe
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.03.2021
• Subjects: 6082 aluminium alloy; Aluminum base alloys; Bend strength; Bending stresses; Corrosion; Corrosion currents; Corrosion mechanisms; Cracks; Electrochemical corrosion; Electrode polarization; Grain boundaries; Intermetallic compounds; Life cycles; Magnesium compounds; Measurement techniques; Metal silicides; Microstructure; passivation; Passivity; Pitting (corrosion); stress corrosion; Yield stress
• ISSN: 0947-5117; 1521-4176
• DOI: 10.1002/maco.202011699

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. The effects of different stresses on corrosion resistance of 6082 aluminum alloy has been studied in NaCl etching solution. The experimental results show that secondary passivation occurred in the passivation interval of dynamic potential polarization curve under the condition of stress. With an increase in stress intensity, the secondary passivation becomes more obvious and the corrosion resistance decreases.