3.2.1. Elongation-to-Failure

Superplastic tensile tests focused on investigating the deformation mechanism at different temperatures, strain rates, and influences of the precipitated phases. The superplastic elongation-to-failure, *δ*, results for the 5A70 alloy are shown in Figure 3.

**Figure 3.** Superplastic elongation-to-failure results (**a**) and the specimens with excellent *δ* values at different temperatures, 400–550 ◦C, and different initial strain rates, 5 <sup>×</sup> <sup>10</sup><sup>−</sup>4–5 <sup>×</sup> <sup>10</sup>−<sup>3</sup> <sup>s</sup>−<sup>1</sup> (**b**).

Figure 3a shows that the elongation-to-failure increased gradually with increasing temperatures and decreasing initial strain rates. Figure 3b shows that the samples were pulled to failure at different conditions, where the top image is the untested specimen. The 5A70 alloy exhibited reasonable *δ* values at 400 and 450 ◦C, with a moderate strain rate. However, excellent superplastic elongation-to-failures gave low strain rates at 500 and 550 ◦C, and the maximum *<sup>δ</sup>* value was 437% at 550 ◦C with <sup>5</sup> × <sup>10</sup>−<sup>4</sup> <sup>s</sup><sup>−</sup>1. In addition, necking was not visible in the superplastic fracture surface and a stable superplasticity elongation was exhibited simultaneously.
