Cryogenic behaviour of Airware 2050 Aluminium Alloy: application for aerospace products in LH2 environment

This study is the fruit of a collaborative work between an aluminum alloy developer and manufacturer - Constellium, a specialist in metallic alloys conversion – Aubert & Duval, and a space launcher designer and manufacturer - ArianeGroup. The aim of this collaboration is to go further in our experience of aluminum alloys for cryogenic use by finding new solutions coupling alloys, transformation process and heat treatment.

The 2219 alloy is commonly used and has demonstrated interesting characteristics for cryogenic launcher tanks. In this study, we focus on 2050, an Airware Al-Cu-Li alloy with a strength level permitting a good compromise between tensile behavior and fracture toughness, even for thick parts, combined with an excellent corrosion resistance, a lower density and a good FSW weldability. This alloy was initially designed for non-cryogenic aircraft applications. The purpose of this study is to test its mechanical behavior down to 20K and extend its use towards cryogenic applications.

Forged blocs and plates were manufactured at different thicknesses and heat treated. Each bloc or plate was cut to sample tensile and fracture toughness specimens that were then tested at room temperature, 77K and 20K. This work abounds the existing results on plates with new data on cryogenic behavior of Airware 2050 forged products. Tensile behavior is presented in L, LT, ST directions, and fracture toughness in L-T and S-L directions. Comparison with plates underlines that Airware 2050 alloy, whether rolled or forged, presents a good compromise between tensile behavior and fracture toughness, with an increase of strength and toughness when the temperature decreases. Compared to 2219 legacy alloy in cryogenic applications, better static and toughness behavior of 2050 at room temperature remains at cryogenic level.