Superplasticity deformation of Ti-6Al-2Zr-1Mo-1V induced by the cyclic change of strain-rate and MaxmSPD

Ti-6Al-2Zr-1Mo-1V is a near α-based Ti-alloy widely used in aerospace industries. Using this alloy to make large and complex-geometry aerospace components, it requires large forming equipment and consumes a great deal of energy. For integral forming of products by using this Ti-alloy, superplasticity deformation (SPD) is a promising process as it increases product strength, reduces product weight, saves materials and uses small capacity equipment. In this paper, the SPD of the Ti-alloy by two different SPD approaches was conducted. The first approach is the SPD induced by the cyclic change of strain-rate; while the other is the maximum strain-rate sensitivity exponent (m) SPD (MaxmSPD). The as-received bulk material was first pre-processed via upsetting and cogging deformation such that the fine microstructure with grain size less than 10 μm was obtained. For the first approach, the strain-rate varied following a continuous variation pattern until the final necking occurred. In addition, three deformation temperatures, viz., 850, 900, 950 °C, and the strain-rate of 5 × 10-5-5 × 10-3 s-1 were employed. The rheological behavior and the effect of process parameters on flow stress and the value of m were investigated. The best elongation of 830% at 900 °C was obtained. For the MaxmSPD, the best elongation of 1066% at 900 °C was identified. The superplasticity capacity is increased by 28.43% compared to the first approach. Therefore, the MaxmSPD has a better SPD capability than the SPD induced by the cyclic change of strain-rate for Ti-6Al-2Zr-1Mo-1V alloy.