| The problem of cracking during repair welding of 2195 aluminum lithium alloy is addressed. 2195 alloy is the primary structural material in the Super Lightweight Tank, which is being developed to enable a critical upgrade of the Space Shuttle System. The cracking is attributed to the existence of a heavy network of shearable lithium-containing precipitates in and near the weld. Two cracking mechanisms are shown to be in operation: Fusion zone re-liquation and creep/rupture. Fusion zone re-liquation occurs at the interface between the original weld and the parent metal; it is best addressed by filler metal selection, employing a strategy of "eutectic crack healing". 4043 is shown to be the best commercially available filler wire for this purpose. Creep/rupture occurs near but not within the repair weld. Filler metal selection can mitigate creep/rupture cracking, but the weld process variables must also be controlled. A thermal stress analysis is presented which is consistent with empirical observations and can be used to develop optimum process parameters for repair welding of 2195 aluminum alloy. |
