Mechanical Properties of Friction Stir Welds in A12195-T8

An extensive study of the mechanical properties of friction stir welded Al-Li 2195 has been conducted by Lockheed Martin Michoud Space Systems under contract to NASA. The study was part of a development program in which weld parameters were defined for using FSW to assemble large-scale aluminum cryogenic tanks. In excess of 300 feet of 0.320 in. gage plate material was welded and tested. The tests include room temperature and cryogenic temperature tensile tests and surface crack tension (SCT) tests, nondestructive evaluation, metallurgical studies, and photostress analysis. The results of the testing demonstrated improved mechanical properties with FSW as compared to typical fusion welding processes. Increases in ultimate tensile strength, cryogenic enhancement and elongation were observed with the tensile test results. Increased fracture toughness was observed with the SCT results. Nondestructive evaluations were conducted on all welded Joints. No volumetric defects were indicated. Surface indications on the root side of the welds did not significantly affect weld strength. The results of the nondestructive evaluations were confirmed via metallurgical studies. Photostress analysis revealed strain concentrations in multi-pass and heat-repaired FSW's. Details of the tests and results are presented.