Comportamiento frente a la corrosión de uniones soldadas por fricción agitación de AA7075-T651: Evaluación galvánica

Abstract

Friction Stir Welding (FSW) is a novel solid-phase welding process, which has proved to have a great potential for the realization of welded joints in materials with poor weldability such as heat-treatable aluminum alloys. The aerospace industry has incorporated this process for the manufacture of structural elements, using known high strength alloys such as AA7075 or AA2024. During FSW, different areas are formed due to the thermomechanical cycle applied, which have been named: the stirred zone (WN), the thermo-mechanically affected zone (TMAZ) and the heat affected zone (HAZ). Each zone presents different metallurgical characteristics, so the corrosion resistance could be affected. This is a relevant aspect for multiple applications and the implications are still not clear. The aim of this work was to study the corrosion behavior of FSWed joints on AA7075-T651. For this purpose, samples of 150x150 mm have been welded with a rotation speed of 680 rpm and two welding speeds: 51 and 206 cm/min. A microstructural characterization of the different zones of the welds was carried out, and the galvanic behavior of the specimens was analyzed through inmersion tests in a solution of 3,5% NaCl without oxygen removal; and agar gel test, by contacting the specimen with a gel membrane prepared with 3% agar, 3.5% NaCl and pH universal indicator solution. Samples for macro and microstructural characterization were extracted. The results showed the presence of a localized attack at the TMAZ-hot HAZ interface. The characterization through SEM indicated a major intergranular attack, with the coalescence of several attacks. In turn, preponderance in the attack was observed on the retreating side of the weld.