Electrochemical Corrosion Behavior of Laser Welded 2205 Duplex Stainless-Steel in Artificial Seawater Environment under Different Acidity and Alkalinity Conditions

The electrochemical corrosion behavior of laser welded 2205 duplex stainless-steel in artificial seawater environment (3.5% NaCl solutions) with different acidity and alkalinity conditions (different pH values) was investigated using different techniques. Namely, capacitance measurements (Mott–Schottky approach), electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The formation of pitting corrosion on the exposure surfaces of the tested duplex stainless-steel samples was investigated and confirmed by characterizing the surface morphology using field emission scanning electron microscope (FE-SEM). Based on the obtained results, a proportional relation has been found between pH value of the solution medium and the generated film resistance due to the processes of charge transfer, which directly affecting the pitting formation and its specifications. Since the film layer composition created on the duplex stainless-steel surface is changes depending on the pH value, it was found that different bilayer structure type was generated according to the acidity or alkalinity level. The presented bilayer is almost composed from metal oxides, such as iron oxide and chromium oxide, as confirmed by Raman Spectroscopy technique. As the pits size and its quantity increased with decreasing pH value, it can be concluded that the corrosion resistance property of the laser welded 2205 duplex stainless-steel sample is improved on the alkalinity direction of the solution. Vice versa, higher acidic solution has more ability for corrosion.