Fatigue characterization and microstructure-sensitive modeling of extruded and friction stir welded aluminum lithium alloy 2099

Abstract

Technological and design advances in military aircraft have dramatically changed the face of war. The need to rapidly deploy troops, military equipment and technology into conflict areas all over the globe, have placed aircrafts in a pivotal role in strategic battlefield operations. While enhanced aircraft designs now allow significantly heavier loads, greater fuel efficiency and higher speeds, there has been little change in the underlying infrastructure and materials that are used to construct the runways that allow these more sophisticated aircraft to successfully land on a variety of terrains in remote areas of the world. For these reasons, there is a need to improve the strength and weight of temporary aircraft matting used to build temporary runways, landing pads, and other readily usable surfaces for transportation applications. Despite the increasing use of aluminum lithium alloys in aerospace applications because of strength and density, the inability to join higher strength Al alloys with conventional welding techniques made it difficult to use in applications that required welding such as the matting for military runways. Aluminum lithium alloys are currently replacing conventional alloys in the aerospace industry. In comparison to other aluminum alloys, enhanced fatigue crack growth resistance, greater specific strength, high fracture toughness, density reduction, stiffness increase, and superior corrosion resistance can be achieved in Al-Li alloys. The ability to provide lower density with comparable strength gives these alloys an advantage over traditional aluminum alloys. However, conventionally welding these Al-Li alloys is difficult and can materially weaken the resulting product. This disadvantage limits a more widespread implementation of Al-Li alloys. Friction stir welding (FSW) offers the capability to join these high strength aluminum lithium alloys, with environmental, metallurgical, and adaptability advantages over other joining techniques. While FSW has been effectively authenticated and studied for traditional aluminum alloys, there is a necessity for understanding the application of FSW to join AL-Li alloys. The purpose of this research is to examine the microstructural and mechanical performance of AA2099 under static and cyclic loading, as well as the effects of the welding process parameters on the microstructure and mechanical performance of friction stir welded AA2099. This study will aid in the implementation of AA2099 in military applications, specifically for producing high strength, light-weight airfield mats for rapid expansions of airfields.