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

Andrey Gnedenkov,Igor Vyaliy,Vladimir Egorkin,Sergey Gnedenkov,Sergey Sinebryukhov,Dmitry Mashtalyar

doi:10.3390/ma11112177

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.

Highlights

In the first part of this work (Part 1) [1], the corrosion behaviour of the bare 1579 aluminium alloy sample with a welded joint was examined through scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET) studies, immersion experiments, and corrosion products’ characterization
To protect the sample against corrosion destruction, the 1579 aluminium alloy specimen with a welded joint was processed by the plasma electrolytic oxidation (PEO) method
The SVET and SIET findings described in the present paper show that a composite protective coating reduces the corrosion activity of treated material in chloride-containing media

Summary

Introduction

In the first part of this work (Part 1) [1], the corrosion behaviour of the bare 1579 aluminium alloy sample with a welded joint was examined through scanning vibrating electrode technique (SVET), scanning ion-selective electrode technique (SIET) studies, immersion experiments, and corrosion products’ characterization. All the obtained results indicate the high corrosion activity of the Al alloy with a welded joint and the necessity of the coating formation to protect this material against intensive corrosion destruction and to increase its stability in the corrosive media. The area of the welded joint was found to be a zone of the corrosion process activation due to the presence of microdefects in the morphological structure.

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Conclusion