Mechanical Joining Characteristics of Aluminum-Lithium in a Production Environment

Aluminum-lithium (Al-Li) alloys have been developed with reduced weight and increased durability characteristics. The application of these new alloys as primary aircraft structure has created the need for refinements in the mechanical joining and stress-coining processes currently employed throughout the aerospace industry. These processes deal specifically with fastener hole preparation, installation processes, and fatigue enhancement techniques associated with stress-coin cold-working methods for mechanical joints. This paper attempts to dispel the myths associated with such processing of 2090 Al-Li alloy sheet and extrusions. Presented are some lessons learned during assembly of the USAF's new C-17A STOL transport airlifter when utilizing Al-Li material.