Dislocation-Controlled Low-Temperature Superplastic Deformation of Ti-6Al-4V Alloy

The superplastic tension and deformation mechanism of Ti-6Al-4V alloy at 923 K and a tensile speed of 10−3, 5 × 10−3, or 5 × 10−2 s−1 was studied on an AG 250KNE electronic tension tester. Through theoretical modeling, the unit dislocation count of this alloy during superplastic deformation was introduced into the Ruano–Wadsworth–Sherby (R-W-S) deformation mechanism map, and a new deformation mechanism map involving dislocation count was plotted. Thereby, the mechanism underling the low-temperature superplastic deformation of this alloy was predicted. It was found the superplastic tension of Ti-6Al-4V at the tested temperature was controlled by dislocation movement, and with an increase in strain rate, the deformation transited from the dislocation-controlled mechanism with a stress index of 4 to the dislocation glide mechanism with a stress index of 5 or 7. At the strain rate of 10−3 s−1, this alloy reached the largest tension rate of 790% and strain rate sensitivity index of 0.52 and had excellent low-temperature superplastic properties.

Theoretical Deduction of Constitutive Equations with Variational Parameters during Superplastic Tension

In this article, firstly, the strain hardening index and the strain rate sensitivity index were deducted from the general state equation and the mechanical meaning of the two indexes were correspondingly depicted, and then constitutive equations, where both/either of the two indexes appear as constants, were theoretically deducted from the same state equation. Secondly, constitutive equations where both/either of the two indexes present as variables were put forward by numerical simulation. Next, constitutive equations were built, where mechanical variables are replaced by test data obtained on an electronic universal tensile tester with the capacity to carry out a true constant strain rate path. Finally, based on the test data of Zn-5%Al during superplastic tension, it is proved that the theoretical results in this article are valid.

Reproducing Kernel Particle Method Numerical Modeling of Thin Sheet Superplastic Tension Forming

Superplastic forming has emerged as an important manufacturing process, large deformation always occurs during superplastic forming, time-consuming remeshing is necessary while the finite element method (FEM) is used to analyze metal forming process. Meshless methods with no meshes can avoid this problem and overcome those problems in FEM. In this paper a meshless method based on the reproducing kernel particle method (RKPM) is applied to analyze Magnesium Alloy (MB15) thin sheet superplastic tension forming. A superplastic meshless method modeling program is set up, and background cells are used to compute the integrations in weak form equations and the mixed transformation method (MTM) is used to impose the essential boundary condition exactly. Numerical example demonstrates the effectiveness of the method in superplastic forming.