Search

Electrochemical noise measurement and analysis enable one to obtain information on corroding systems without applying any potential or current perturbation to the corroding surface, and they are thereby nondestructive techniques, suitable for corrosion monitoring. The measurement process requires converting the analog potential or current signal in a digital dataset that can be used to perform mathematical operations with a variety of approaches. The analog-to-digital conversion is a critical step since, after the conversion has been performed, it is impossible to correct for artefacts that occurred during the conversion. Additionally, the electrochemical noise generated during corrosion is generally overlapped to the instrumental noise and to the electrical interference that are present in the environment where the measurement is performed. In this work, the process of analog-to-digital conversion of electrochemical noise signals is analyzed in detail by simulating the conversion of a representative simulated noise signal. With this approach, the possible issues arising from the analog-to-digital conversion process are highlighted and the key features arising from instrumental noise, aliasing, and electrical interference are identified.

Friction Stir Welding (FSW) and Laser Welding (LW) can be successfully employed to weld aluminium alloys, in many cases overcoming the difficulties encountered with more conventional welding processes like MIG or TIG. The corrosion resistance of the welded joint remains, however, an important issue, especially in applications (like in aircrafts), where corrosion can induce structural failure: the weld region has often lower mechanical resistance in comparison with the parent material and a decrease in its corrosion resistance, especially when the corrosion damage can represent a potential crack initiation site, can be unacceptable in components design. In this work the corrosion resistance of welded T-joints produced with FSW and LW on different 6xxx aluminium alloys is investigated. These alloys offer good mechanical properties and high corrosion resistance and are often used in aircraft fuselage components. Processes like FSW or LW, however, can induce, in age-hardenable alloys like the 6xxx ones, significant metallurgical modifications and consequent changes in the electrochemical reactivity. This work proves that, if the alloys and the welding parameters are chosen correctly, for both FSW and LW it is possible to obtain welded joints such that galvanic couple established between the welded region and the parent material results in preferential attack of the latter: this drives corrosion away from the weld region and reduces the cathode/anode area ratio, improving the corrosion performance of the whole weld.