Assessment of Aluminum Lithium Alloys for Primary Aircraft Structures

The latest generation of advanced aluminum-lithium (Al-Li) alloys offers weight savings compared to conventional aluminum alloys, while maintaining mechanical performance.  Al-Li alloys have a lower density, higher modulus, and improved resistance against corrosion over the widely used 7xxx and 2xxx series alloys.  While previous generations of Al-Li exhibited issues with their mechanical properties, which limited their use in aerospace applications, the latest generation of Al-Li alloys is reported to have minimized these effects.  With these improvements, there has been increased use of Al-Li in recent aircraft and aerospace applications.  Although there have been substantial propriety data generated to substantiate structural applications, there is a lack of data available in the public domain to thoroughly document the material’s mechanical performance. 

As a case study, two Al-Li alloys were considered; namely, 2198-T8 and 2196-T8511 alloys used for skin and extrusion applications, respectively.  Resources and expertise were leveraged from several organizations, including Constellium, Bombardier, National Aeronautics and Space Administration-Johnson Space Center, Naval Air Systems Command, University of Dayton Research Institute, Drexel University, National Institute for Aviation Research, and the Federal Aviation Administration William J. Hughes Technical Center.  Several properties were assessed and compared with baseline 2024-T3 and 7075-T6 alloys, including static properties; fatigue life and fatigue crack growth behavior; and supplemental properties.  Although static test results indicated anisotropic behavior in the Al-Li alloys, particularly at the off-axis 45° grain orientation, measured static properties exceeded published Metallic Materials Properties Development and Standardization Handbook allowables.  In general, fatigue test results revealed better fatigue crack growth resistance and longer fatigue lives for the Al-Li alloy compared to the baseline material; however, unique cracking behavior was observed in the 2198-T8 material when tested in a lap joint configuration.  This presentation will highlight the significant results generated by the program to date.