Effects of Aging Treatment on Corrosion Behavior of a Tensile Deformed Al-Cu-Mn-Fe-Zr Alloy in 3.5% NaCl Solution

Abstract

In this paper, the effects of an aging treatment on the corrosion resistance/mechanism of a tensile deformed Al-Cu-Mn-Fe-Zr alloy are investigated. The impedance magnitude and polarization resistance increase, while the corrosion current decreases with the increased aging time and temperature. The discontinuously-distributed precipitates and precipitation-free zone, which can cut the corrosion channels, appear at grain boundaries when the temperature is relatively high and the aging time is relatively long. They can improve the corrosion resistance. Additionally, the intergranular and pitting corrosion are the main mechanisms. The intergranular corrosion is likely to occur in an under-aged alloy. This is because the potential difference between the grain boundaries and grains is high, due to the segregation of Cu atoms. When the aging degree is increased, the grain boundary precipitates reduce the potential difference, and the intragranular precipitates make the surrounding matrix prone to dissolution. As such, the pitting corrosion is likely to occur in the over-aged alloys.

A Comparative Study of Corrosion AA6061 and AlSi10Mg Alloys Produced by Extruded and Additive Manufacturing

“…For the characteristic of the poor passive layer, the localized attacks began to diffuse after a time, so high energy was presented at low frequencies indicating pitting diffusion. Other authors such as Lin et al [ 72 , 73 ] commented that in order to improve the corrosion resistance of light alloys it is important to consider the effect of precipitate pretreatments on the microstructure, seeking to ensure that they are well distributed. The concentration of precipitates of Cu, Zn, or Mg can cause cracks or failures in the alloys, and this was reflected in the transients of the electrochemical noise-generating drops in potential and increase in the current [ 72 , 73 ].…”

Evaluation of the Effect of Dual-Stage Aging and RRA on the Hardening and Corrosion Resistance of AW7075 Alloy

“…The presence of precipitates at the grain boundaries of GBPs in the material microstructure resulted in a large potential difference between the anodic grain boundary and its cathodic center. It is suggested that as the aging stage deepened, alloy segregation occurred, leading to an increase in the copper content of GBPs as a result of the η phase moving toward equilibrium content [2,12,18,41,44]. The size, spacing, and copper content of GBPs after RRA treatment increased as the aging step deepened, which is beneficial for the grain boundary to resist anodic dissolution [43].…”

“…This reduces the driving force for local corrosion and contributes to improved resistance to intergranular corrosion [43]. At the same time, grain centers become susceptible to dissolution [44]. In the RRA state, the MPs precipitates are also enriched in copper, which further promotes the reduction of copper content in the matrix [47].…”

“…When the aging level increases, the precipitates at grain boundaries reduce the potential difference, and the intra-grain precipitates make the surrounding matrix more susceptible to dissolution. Therefore, pitting corrosion is more likely to occur in aged alloys [44]. The AW7055 alloy after RRA treatment showed better corrosion resistance than single-stage aging with 10% hardness loss [7].…”