Microstructural refinement of weld fusion zones in alpha-beta titanium alloys using pulsed current welding

Pulsing of the welding current is one approach for refining the fusion zone grain structure in alpha-beta titanium alloy welds. This paper reports wor k in which gas tungsten-are welds were produced in two alpha-beta titanium alloys under a variety of conditions including direct current (d.c.) pulsin g and alternating current (a.c.) pulsing. The results show that, while d.c. pulsing did also refine the weld metal beta grain structure, the effect of a.c. pulsing was much greater. Current pulsing enhances fluid flow, reduce s temperature gradients and causes a continual change in the weld pool size and shape. These effects, which are believed to be responsible for refinin g the solidification structure, are much stronger in a.c. pulsing than in d .c. pulsing. The observed grain refinement was shown to result in an apprec iable increase in fusion zone tensile ductility. Post-weld heat treatment i mproved ductility both in pulsed and unpulsed welds. but pulsed welds showe d greater tensile elongation even in the heat treated condition. (C) 1999 E lsevier Science S.A. All rights reserved.