Hydrogen effect on the electrochemical behavior of aluminum alloys welded by friction stir welding (FSW)

Abstract

In this project, the effect of hydrogen intake from one side of samples of AA2024 / AA7475 alloys welded by Friction Stir Welding (FSW)and its release at the opposite side will be studied. The local electrochemical characterization of the different regions of the weld will be carried out. To perform this evaluation, an electrochemical cell with a double compartment separated by a membrane made by the AA2024 / AA7475 alloy sample welded by FSW will be used. In one compartment, hydrogen will be cathodically generated on the face of 1 cm2 of the sample exposed to 3.5% NaCl solution and in the other compartment, the region at the opposite face of the weld will be delimited by a ring of 1,5 mm diameter in contact with the solution of Na2SO4 0.1 mol L-1 + NaCl 0.010 mol L-1. The aim of this study it to understand the influence of permeated hydrogen on the corrosion processes that can occur in the different regions affected by welding: thermally affected zone (ZTA), thermomechanically affected zone (ZTMA) and region of the mixture (ZM), also known as a nugget, and the base metal. The surface morphology of the samples will be studied by optical microscopy (OM), scanning electron microscopy with field emission gun (FEG-SEMSEM / FEG) and analyzed by X-ray energy dispersion spectroscopy (EDXS), before and after the electrochemical tests. The surface of the samples will also be analyzed by atomic force microscopy (AFM). The surface of the sample welded by FSW, after preparation, will be characterized by electrochemical tests in the different regions of the weld by open circuit potential measurements as a function of time (EOC-t), polarization curves (CP), cyclic polarization curves (CPC) and electrochemical impedance spectroscopy (EIS).