Aluminum alloys, because of their face-centered cubic structure, offer distinct advantages as structural materials for use at cryogenic temperatures, at which some other metals are brittle. Accordingly, tests of seven alloys (2014-T6, 2219-T62, 5456-H321, 6061-T6, 7075-T6, 7079-T6, and 7178-T6) using smooth and sharply notched, longitudinal and transverse specimens of plain and welded 1/8-in. sheet were made at 75, −320 (liquid nitrogen), and −423 F (liquid hydrogen). As parent metal, all alloys were found to be suitable for use at these temperatures, exhibiting ductile behavior throughout the full temperature range. For welded structures or in applications where notch sensitivity is important, the use of some of the higher strength heat treated alloys may necessitate special precautions in design. While as-welded joints in each alloy had lower strengths than the parent metal at all temperatures, welds in alloy 2219-T62 when reheat treated had strengths equal to those of the parent metal. The sharp-notch sensitivities of welds in some alloys were less than those of the parent metals.