Effect of Grain Size on the Mechanical Properties of Aluminum Alloy AA2219 Parent and Weldments at Ambient and Cryogenic Temperature

Aluminum alloy AA2219 is used for the fabrication of the liquid hydrogen (fuel, boiling point 20 K) and liquid oxygen (oxidizer, boiling point 90 K) propellant tanks of cryogenic engine in view of its good weldability, compatibility with propellants and excellent mechanical properties at the operating temperatures. The propellant tanks are fabricated using fine-grained thin sheet/plate, roll bent to form cylindrical shells and are welded to large coarse-grained intermediate/end seamless ring-rolled products. The integrity of the weld joints and the mechanical properties need to be ascertained for the joints with coarse- and fine-grained microstructures to demonstrate the safety margins on the tank design. Therefore, detailed experiments were conducted to study the effect of grain size and grain aspect ratio on the mechanical properties of AA 2219 parent and weld specimens, at both ambient and cryogenic temperatures. It was found that reliable joints could be fabricated and there was no significant effect of grain size or aspect ratio on the mechanical properties of weld joints either at room temperature (300 K) or at 77 K.