Abstract : Preliminary conclusions regarding the weldability of 0.005-inch D-31 alloy foil are: (1) new D-31 possesses good ultrasonic weldability. Crackfree welds with good tensile-shear consistency can be made; (2) good ultrasonic welds can be attained over a consderable power range: 850 watts with the 0.25- inch spherical sonotrode-tip radius to 1600 watts with the 0.75-inch tip radius; weld strengths consistency is good, standard deviation is low; (3) the material is somewhat sensitive to clamping force; (4) D-31 seems to be senitive to tip surface condition and to surface cleanliness; (5) although good welds may be made with low power and low clamping force, better consistency and higher- strength levels are obtained with higher power and higher clamping force; (6) welding slightly below minimum clamping force yields poor results; (7) the most suitable sonotrode-tip radius appears to be 0.5 inch; and (8) material quality appears to exert a paramount controlling effect on weld qulity, strength level, and consistency.