Effect of the displacement control routine on the elongation to failure and failure morphologies in superplastic AA-5083

It has been noted in the literature that superplastically formed Al alloys fail by cavitation. The morphology of the final cavitated fracture region may be important in determining optimum forming conditions, specifically by determining the angle of the fracture relative to the principal stresses. In addition, the displacement control routine may have a large effect on the total elongation that can be expected during forming operations. Tests were performed to evaluate failure in a AA5083-base alloy, by the following methods: 1) uniaxial tension tests at a constant true strain rate were interrupted at 80%, 60%, 40%, and 0% of the maximum load, and microstructurally evaluated to identify the failure path and 2) tests were performed with various displacement control routines, and the elongation to failure was measured. The following displacement routines were used: smooth test, two-step strain test, multi-bump strain rate tests with various sizes of bumps scheduled at various intervals, and variable load oscillation tests.