Aluminum alloys are used in a wide range of engineering applications and are gaining increasing usage in the construction sector, offering high strength-to-weight ratios and good durability. In this paper, a series of stub-column tests on aluminum alloy box sections with and without internal cross stiffeners is carried out to investigate cross-section capacity and to explore the possible exploitation of strain hardening in design. All existing stub-column test results from the literature were also collected. A database containing the results from 346 tests on aluminum alloy stub columns of box, channel, and angle sections, with a wide range of cross-section slendernesses, was formed. The test strengths were compared with the design strengths predicted by the current American, Australian/New Zealand, and European specifications. Furthermore, the test strengths were compared with those predicted by the deformation-based continuous strength method (CSM). Following reliability analyses, the design strengths predicted by the three current design specifications were found to be generally conservative, whereas the CSM offered improved design capacities, owing to its allowance for strain hardening.