The Effect of Preheating on Notched Tensile Strength and Impact Toughness of Ti-6Al-6V-2Sn Laser Welds

Abstract

Notched tensile strength (NTS) and impact toughness were determined for Ti-6Al-6V-2Sn laser welds subjected to post-weld heat treatment (PWHT) at distinct temperatures. In this study, the specimens were either preheated at 300 C or maintained at room temperature before laser welding. The preheated weld, associated with a reduced cooling rate, had obviously lower hardness than the non-preheated weld in the as-welded condition. After PWHT at 482 C for 3 h, the preheated weld also exhibited considerably lower hardness than the non-preheated weld. In general, preheating at 300 C could effectively increase the NTS and impact toughness of Ti-6Al-6V-2Sn laser welds. The preheated weld in the as-welded condition had superior NTS to other welds being tested. On the other hand, the welds after PWHT at 704 C possessed the best resistance to unstable impact fracture, regardless of preheating. Usually, the coarse þ structures together with intergranular were responsible for the high NTS and impact toughness of the weld.

Notched Tensile Fracture of Ti–6Al–4V Laser Welds at Elevated Temperatures

“…The results were compared with those of millannealed Ti6Al4V specimens and Ti6Al6V2Sn welds. 12,14) The decrease in NTS and the change in fracture characteristics of the specimens with temperature were also correlated with the fracture features.…”

“…In addition, the high notch sensitivity of such high-strength titanium laser welds can be reduced by preheating prior to welding. 13,14) In the case of the Ti4.5Al3V2Mo2Fe weld after PWHT at 704°C, the formation of grain boundary ¡ layers, which promote grain boundary shear, is believed to decrease the notch sensitivity of the weld at room temperature. 10,13) As a general rule, the applications of titanium alloys are restricted to temperatures below 550°C.…”