Investigation on the electrically-induced stress relaxation behaviour and constitutive modeling of Ti-6Al-4V titanium alloy

Abstract

Electrically-assisted forming (EAF) has been widely applied in the manufacturing of titanium alloy sheets. The stress evolution is influenced not only by the forming process but also by stress relaxation during the pressure-holding phase, which ultimately leads to springback. Currently, the impact of current on the short-term stress relaxation behavior of titanium alloys has not been thoroughly investigated. This study focuses on the short-term stress relaxation behavior of Ti-6Al-4V titanium alloy under electric current. A series of relaxation tests were conducted at several DC current densities (ranging from 3.75 to 6.56 A/mm²) and plastic strain levels (ranging from 1% to 10%) to obtain stress relaxation curves. The experimental results reveal that the stress relaxation behavior of Ti-6Al-4V under electric current exhibits a short-term rapid characteristic. Furthermore, the increase of current density and strain level significantly accelerates the relaxation process and enhances the stress release percentage. In this study, both exponential and logarithmic models were applied to the electrically-induced stress relaxation curves of Ti-6Al-4V titanium alloy. Based on a logarithmic model that considers the variation of movable dislocation density, a current parameter correction factor was introduced to establish an electrically-induced stress relaxation constitutive model. Model parameters were identified, and the prediction results demonstrate that the proposed model accurately describes the electrically-induced stress relaxation behavior of Ti-6Al-4V.