Effect of Composition and Aging Treatment on the Microstructure and Mechanical Properties of Aluminum-Lithium-Titanium Alloys.

摘要

Aluminum lithium alloys have recently been recognized for their potential as aerospace alloys. Al-Li alloys offer the combination of high strength and elastic modulus with low density, thereby resulting in substantial weight and cost savings. The precipitation of the metastable Delta' (Al3Li) phase upon aging provides considerable increases in strength. The major problem encountered thus far is that the Delta' phase, due to its shearable nature, causes slip localization, reducing ductility and fracture toughness. The present study is based on the theory that by altering the precipitation behavior and characteristics by additions of titanium it will be possible to disperse slip and consequently increase fracture toughness. Titanium has been selected as the alloying element because in the Al-Ti binary system Al3Ti forms with lattice parameter and crystal structure similar to those of Al3Li. The mechanical properties of the alloys have been determined at several aging conditions. The strength of the alloy increases significantly at each aging condition as titanium is added to the system. Elongation to failure remains fairly constant with titanium additions, but fracture toughness drops as higher amounts of titanium are added. The 3Li-0.2Ti alloy shows the best combination of strength and toughness. (kt)