TWI carried out welding trials using a novel wire produced by Daido Steel called G-coat. The main objective of the project was to determine if the quality concerns previously associated with GMAW welding of titanium, such as weld spatter and porosity, could be overcome.

Pulse parameters were optimised using Ti6Al4V plate and once stable conditions were established, butt welds and fillet welds were produced in 7mm thickness material and butt welds also produced in 4mm material.

Welds were analysed visually and non-destructively in accordance with AWS D17.1. It was found that the 7mm butt welds met the Class A requirements of D17.1 including internal porosity, surface appearance and no spatter was evident.

Only limited information is available concerning the surface modification of the wire however, it is thought that the improved transfer is achieved by controlling the oxide layer on the surface of the wire. This results in the surface tension of the molten titanium being reduced, facilitating droplet detachment at lower pulse energy.

The use of the G-coat wire has been shown to have benefits for GTAW welding in processes such as manual edge build up, where small droplet deposition is required and also in the Air Liquide TOPTIG™ at high deposition rates.

In conclusion TWI have found that through the use of optimised pulse parameters and a novel wire, aerospace quality GMAW welds can be produced economically and to a high standard of quality. TWI is interested in further development of the process for industrial applications.