Effect of aging on the corrosion behavior of 6005 Al alloys in 3.5 wt% NaCl aqueous solution

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Xia Chen The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China

Bin Chena) School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China (Received 20 January 2018; accepted 30 March 2018)

The effect of aging time on the corrosion behavior of 6005 Al alloys has been investigated in aerated 3.5% NaCl aqueous solution. The corrosion resistance of the alloy with different aging times is analyzed by measuring potentiodynamic polarization, electrochemical impedance spectroscopy. The surface morphology is examined by scanning electron microscopy. The results demonstrated that the corrosion resistance of the alloy in the peak-aged condition is worse than the other conditions. Accordingly, corrosion rate and the corrosion current density of the alloy reach its maximum value. An Fe-rich phase is identified as the b-Al4.5FeSi phase by atomicresolution high angle annular dark field scanning transmission electron microscopy and energy dispersive X-ray spectroscopy mapping analyses. The b-Al4.5FeSi is wrapped slowly by the precipitates of Mg2Si from the process of the peak-aged condition to the over-aged condition. It is hypothesized that the change of corrosion behavior of the alloy may be attributed to the b-Al4.5FeSi wrapped slowly by the precipitates of Mg2Si.

Aluminum is a lightweight metal with the characteristics of low density, low price, high electrical conductivity, and high energy density. Aluminum and its alloys are widely used in many fields, especially in aerospace and household industries.1,2 As one of the heat treatable aluminum–magnesium–silicon alloys, 6005 alloys having the advantage of moderate strength, excellent corrosion resistance, and good welding performance in atmosphere environment are widely used for high-speed trains, subway trains, automobile body, double-decker trains, and other industrial structural profiles at home and abroad.3 However, a major problem with the application of 6005 alloys is that its corrosion rate and mechanical properties deteriorate in moist and seawater environment. Thus investigating the corrosion behavior of the alloy is very important. Most of the researchers believe that precipitation plays a significant role in corrosion of the 6000-series aluminum alloy. The main elements of the 6000-series aluminum alloys are Si and Mg, which are partly dissolved in the a-Al matrix and form the phase of Mg2Si. The precipitates a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.86

can be controlled by heat treatments and artificial aging and also have a positive influence on the mechanical strength and hardness of the alloys. The precipitation of the equilibrium b(Mg2Si) phase will undergo a series of changes during the aging process. The precipitation sequence during aging in 6000-series aluminum alloys conforms to the general scheme described for the ternary Al–Mg–Si alloys: supersaturated solid solution (SSSS) ! solute clusters ! GP-Ι zone

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