The Effect of Indium Additions on the Cryogenic Tensile Properties of Superplastically Deformed Al-Cu-Li-Zr Alloy 2090

Abstract

Superplastic aluminum-lithium alloys are promising aerospace materials based on their high stiffness and low density, as compared to other superplastic aluminum alloys, and their ability to be formed to complex shapes that minimize weight. However, superplastic forming precludes the use of a pre-aging stretch which promotes homogeneous nucleation of T1 (Al2CuLi) and is a partial source of the excellent properties of 2090. Indium was added to superplastic 2090 in order to improve the post-formed mechanical properties. Tensile tests performed at 300 and 77 K show that the strengths are better than those demonstrated for regular 2090 after superplastic deformation. Failure occurs by transgranular shear and intergranular separation at 300K in both the formed and unformed material. At 77K failure occurs intergranularly prior to the geometric tensile instability, which is consistent with brittle fracture. It is believed that grain boundary intermetallics are promoting this fracture mode change at low temperatures.