CorALiS

In recent years, aluminium–lithium (Al–Li) alloys have gained importance as structural materials for aerospace components. Addition of Li to aluminium increases the elastic modulus of the material and also decreases the density. This unique combination resulting in high specific strength and modulus for airframe structures allows increasing the fuel efficiency of aerovehicles and helps to protect environment. The friction stir welding (FSW) technology is being targeted by modern aerospace industry for high performance structural applications. Of particular interest is FSW of high strength aluminium alloys for aerospace applications, where cost and weight savings are possible by replacing riveted joints with friction stir welds. This advantage makes FSW promising for industrial application since these alloys allow a considerable lightening of structures. However FSW technology requires a through understanding of this technique and the evaluation of consequent welds mechanical properties is needed in order to use the FSW process for production of components in aerospace applications. With this aim, EADS and Alcan have studied and developed FSW process for Al-Li alloys. Its main advantage is its capability to weld successfully some metallic alloys like Al-Li which cannot be welded by traditional fusion welding processes. However, the effects of this complex thermal and thermo-mechanical process on the microstructure and corrosion resistance of Al-Li friction stir welds have yet to be determined. This project, based on industrial applications, is undertaken to characterize corrosion (intragranular, intergranular or exfoliation) and stress corrosion mechanisms susceptible to occur on Al-Li alloy 2050 friction stir welds in order to predict their lifetime under these type of conditions. The 2050 alloy, provided by Alcan, is a third generation Al-Li alloy expected to be used for aerospace components in the future. The aims of this project are: 1. to study Al-Li alloy 2050 friction stir welds metallurgy; 2. to determine the influence of metallurgy, environment and internal stresses on corrosion and stress corrosion damages of Al-Li 2050 alloy; 3. also to characterize the Al-Li alloy 2050 friction stir welds behaviour under corrosion conditions; 4. to evaluate initiation and growth of corrosion defects taking into account pertinent parameters and to be able to purpose propagation rules in a reduced time 5. to predict the evolution of internal stresses distribution during adapted mechanical tests taking into account environment, samples geometry and loading; 6. to evaluate the effects of FSW process on welds mechanical properties; 7. to reduce corrosion damage optimizing Al-Li alloy 2050 friction stir welds microstructures in order to increase their corrosion resistance. Finally this project, based on experimental tests and simulation works, should contribute to the introduction of Al-Li alloy 2050 friction stir welds into aeronautic structures.