Advanced Aluminum Alloys and Technologies for Liquid Hydrogen Tanks

Liquid Hydrogen (LH2) tanks have been developed in recent decades for spacecraft with 2219 T8 selected for most components due to its fusion weldability, good mechanical properties and good cryogenic behavior. Today, new applications are developing such as reusable launcher structures, Hydrogen propelled aircraft projects and other applications with high build rates. In addition, new assembly techniques like Friction Stir Welding or improved forming techniques are developed. This justifies the reconsideration of alloy choices in the light of the metallurgical developments seen in recent years.

From a general point of view, Aluminum alloys remain a good choice for LH2 tanks thanks to their impermeability to gases, the absence of embrittlement in dry Hydrogen, their light weight and good materials properties, retained at cryogenic temperatures for most alloy families.

More specific design drivers regarding aircraft LH2 tanks will be presented, in particular looking at requirements for long durations: fatigue and damage tolerance, corrosion. Evaluating the damage tolerance of high toughness alloys in principle requires large specimens, e.g. to measure the KR-curves (ASTM E561). This might be impractical in LH2 environment so that a combination of sub-sized specimens and modeling is proposed.

Airware® Al-Cu-Li alloys have proven their technical – economical interest on recent launchers. Their excellent damage tolerance and corrosion properties should make them good candidates for new LH2 tanks. Other alloy options are also on the table and will be presented.