An Update on C458 Al-Li

The 1.8 Li content and consequently the 0.0945 lb.cu in density of C458 along with its higher modulus and good strength and toughness at ambient and cryogenic temperatures made it an attractive alloy for single and multiple use cryogenic tankage and unpressurized structure for space launch and operational vehicles. A major effort during the past year was directed towards establishing a production capability for C458 plate. Alcoa established a production ingot casting capability under Air Force Research Laboratory and NASA's Space Launch Initiative (SLI) sponsorship. Three heat lots of material were rolled so that the criterion for S-basis allowables could be met for AMS specifications. Lot acceptance testing showed that the strength and toughness values equaled and exceeded those obtained under the earlier Air Force Program when the alloy was developed. The details of this effort and the results achieved will be described. During the testing of compact tension specimens, particularly at cryogenic temperatures, delaminations were noted on the fractured surface. An investigation was initiated to better understand this condition. The results of this investigation will be presented which includes some of the successful production application of alloys with and without Li that exhibit this type of behavior.