Development of 2050 T62 for spin forming and similar applications

Cryogenic tankage and dry structures of space launch vehicles require domes and similar circular bulkheads. One of the methods to fabricate these shapes is thru a spin forming process. This process enables production of cones, domes, caps and bulkheads. Future applications may include circular lightweight components for lunar habitats and landers. Smaller domes can be fabricated from a singular piece. Larger domes i.e. greater than 5 meters typically utilize the more complex FSW welded with a smaller dome cap. Legacy domes for space launchers frequently use spun formed 2219-T62 plate. Material is delivered as circular stock in either O or F temper. Input thickness is typically 1.5-3.0” but not limited to that gauge range. Circular blanks are spun formed with plate heated in the range of 450-550°F. After forming domes are solution heat treated to T42. Final T62 properties are achieved via one step age in the range of 330-350°F. Typical Yield Strength of T62 domes based on coupons cut from the edge or dome cap is in the range 42-44ksi.

Based on AEROMAT 2022 presentation which featured 2050 Friction joined spun formed domes (Michael Eller at el) Constellium decided to develop statistically derived 2050-T62 mechanical properties to ensure that space launch OEM can take advantage of this advanced Al-Li alloy. Alloy 2050 features 30% higher static properties when compared to 2219 irrespective of the temper coupled to best in its class SCC resistance. It is 5% lighter and features 5% higher modulus. We felt that combination of these attributes may result in a much lighter and yet stronger structure. We learned that some customers emphasize static properties while others prefer material with high fracture toughness. Therefore, we took two parallel paths to develop both sets of properties. Test coupons were annealed and then solution heat treated to develop T42 temper. Aging practices were selected to provide two sets of TYS/FT data bases. Beyond tensile properties we were able to ascertain that T62 has similar SCC resistance behavior to T84 temper and will not be susceptible to this form of corrosion. Results indicate that 2050 is superior to 2219 in the T62 temper. Aluminum Association registration and AMS spec documentation is underway