Characterization of Ti-6Al-4V alloy in the temperature range of warm metal forming and fracture analysis of the warm capping process

Abstract

The flow behavior of a Ti–6Al–4V alloy during warm forming was characterized, and the results were analyzed to reveal the causes of fracture during warm forging of a small Ti–6Al–4V alloy bolt. The experimental flow curves obtained by compression test of cylindrical specimens at the warm forming conditions were fitted by a general extended C–m model after post-processed by a high-accuracy temperature correction scheme. Finite element analyses of the compression tests were conducted at various sample temperatures and strain rates using the flow model, revealing that the predicted compression loads were consistent with the experimental results. Flow behavior was also analyzed to reveal the metallurgical and macroscopic instabilities of the Ti–6Al–4V alloy. The flow behavior, macroscopic instability indices, and predicted forming load-stroke curves of Ti–6Al–4V alloy and SCr420H alloy steel were compared. The results study revealed that fracturing of the material in the capping stage during the automatic multi-stage warm forging of the small Ti–6Al–4V alloy bolt was caused by the sharp decrease in the forming load in an unpredictably early stroke from macroscopic instability, as indicated quantitatively by its macroscopic instability index.