Corrosion of the Welded Aluminium Alloy in 0.5 M NaCl Solution. Part 2: Coating Protection

Abstract

The high electrochemical activity of the aircraft 1579 aluminium alloy with a welded joint and the necessity of the coating formation to protect this material against corrosion as well as to increase the stability of the weld interface in the corrosive medium has been previously established. In this work, two suggested methods of protective coating formation based on plasma electrolytic oxidation (PEO) in tartrate-fluoride electrolyte significantly increased the protective properties of the welded joint area of the 1579 Al alloy. The electrochemical properties of the formed surface layers have been investigated using SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique), EIS (electrochemical impedance spectroscopy), OCP (open circuit potential), and PDP (potentiodynamic polarization) in 0.5 M NaCl. The less expressed character of the local electrochemical processes on the welded 1579 Al alloy with the composite coating in comparison with the base PEO-layer has been established. Polymer-containing coatings obtained using superdispersed polytetrafluoroethylene (SPTFE) treatment are characterized by the best possible protective properties and prevent the material from corrosion destruction. Single SPTFE treatment enables one to increase PEO-layer protection by 5.5 times. The results of this study indicate that SVET and SIET are promising to characterize and to compare corrosion behaviour of coated and uncoated samples with a welded joint in chloride-containing media.

Effect of Cooling Rate at the Eutectoid Transformation Temperature on the Corrosion Resistance of Zn-4Al Alloy

“…This is most likely due to the formation of a corrosion product film on the surface of the α phase that protects it from further corrosion, in accordance with other works [18,24,34]. Thus, changing the anodic zone polarity due to the formation of a protective film can be used in corrosion protection [38]. After reaching a potential of −675 mV vs. Ag/AgCl (+450 mV vs. Ecorr) the current density decreased on the potentiodynamic curve ( Figure 6).…”

Effect of Electrode Waterproof Coating on Quality of Underwater Wet Welded Joints

“…Gnedenkov et al [42] proposed composite polymer-containing protective coatings to significantly improve both the protective and antifriction properties of the surface of magnesium alloys. The hydrophobic coatings can be also used as protection for welded joints, which was proved by Gnedenkov et al [43]. It was stated that plasma electrolytic oxidation coating decreases the susceptibility of welded joint to corrosion.…”

Effect of Microstructure on the Corrosion Resistance of TIG Welded 1579 Alloy

“…The results of the images analysis of BM (Figure 3a), HAZ (Figure 3b), and FZ (Figure 3c) are conformed to data of optical images shown in Figure 2. Due to the highest volume fraction of secondary phases in the heat affected zone and based on previous studies [20,21], an assumption was made about higher corrosion activity of HAZ as compared to BM and FZ.…”

“…Aluminum alloys of the Al-Mg-Sc system combine such properties as medium-strength, high corrosion resistance and possess high weldability. In our previous studies [20,21] we have established using localized electrochemical methods that weld interface of 1579 Al alloy is an area, where corrosion starts. At the same time, we have not correlated this specific place of weld interface, where the corrosion process occurred, with the microstructure of the material.…”