TESTING THE SUPERPLASTIC FLOW CHARACTERISTICS OF ADVANCED ALUMINUM-ALLOYS

Special test equipment is required in order to determine the superplastic flow characteristics of advanced aluminum alloys such as the low-density aluminum-lithium alloys and the high-temperature intermetallics (processed by rapid solidification, mechanically alloying, powder metallurgy techniques). The superplastic flow characteristics under optimum conditions of strain rate and temperature are necessary as input data to the computer process model used to predict optimum pressure-time cycles for the SPF process. Most published tensile flow stress data for superplastic deformation was developed under constant crosshead speeds and at atmospheric pressure. In order to establish accurate flow characteristics, testing must be conducted: (1) at a closely controlled temperature, (2) at a controlled constant true strain rate, and (3) under hydrostatic pressure (to prevent cavitation). This paper discusses the design and development of a test system with these capabilities and also highlights typical results for three aluminum-lithium alloys.