Fatigue Behaviour of Aluminium Lap Joints Produced by Laser Beam and Friction Stir Welding

Railways passenger transportation seeks weight reductions as a means to reinforce its sustainability. The use of aluminium alloys for the vehicle car bodies is a possible alternative, but difficulties are foreseen concerning the fatigue behaviour of the connection of heavy equipment to the underside of the structural floor panels. This study was conducted within the LighTRAIN project, involving two universities, two industrial companies and one research centre, that aims to improve the life cycle of the underframe of a passenger railway car, with a novel light-weighted solution. The main objective of present work was to study the fatigue behaviour of 2.0 mm thick aluminium AA6082-T6 welded joints based on two different welding processes: Friction Stir Welding (FSW) manufactured at Instituto Superior Tecnico (IST) and Laser Beam Welding (LBW) manufactured at QUANTAL. The paper presents the experimental results obtained in tensile and fatigue tests of welded lap joints. The specimen types include the loading condition applied to the specimen in a transverse or longitudinal direction to the weld bead. The fatigue tests were carried out under a constant amplitude loading with a stress ratio R=0.1 for a wide range of applied stress. The mechanical behaviour, including microstructural, microhardness, tensile and fatigue tests results of AA6082 2.0 mm thick FSW welded joints are compared with LBW welded joints in the framework of the aforementioned QREN project. Moreover, details of fracture surfaces obtained with optical microscopy are also presented. (C) 2014 Published by Elsevier Ltd.