Thermomechanical processing of welded α +β Ti-AI-Mn alloy and its effect on microstructure and mechanical properties

In α + β titanium alloys, microstructures containing equiaxed α grains exhibit greater ductility and those with lamellar α higher fracture toughness. Weld fusion zones, which are in essence quenched from the βphase field, have a lamellar α morphology. The present paper reports work aimed at studying the possibility of obtaining bimodal (equiaxed + lamellar) structures in weld metals, which may he expected to possess an optimum combination of tensile elongation and toughness. Electron beam weld fusion zones in a Ti-AI-Mn alloy were subjected to suitably designed thermomechanical treatments for producing fully equiaxed and bimodal microstructures. Simple post-weld annealing treatments were also applied. Tensile ductility and fracture toughness were measured, using the instrumented Charpy impact test for the latter. The structural changes during welding and the various post-weld treatments and their effect on the two mechanical properties are discussed. © 1997 The Institute of Materials.