Aluminum alloys have been widely used in the constructing various space structures including the International Space Station (ISS) and launch vehicles. For space application, welding experiments of an aluminum alloy were conducted by the GHTA (Gas Hollow Tungsten Arc) welding processes using a filler wire feeder in vacuum. We investigated the melting phenomena of a base metal and a filler wire, bead formation phenomena and effects of wire feeding speed on melting characteristics. The melting phenomenon of melt-run welding with a filler wire was basically the same as that of without a filler wire. It was clarified that the effects of wire feeding speed on bead sizes and configurations. Furthermore the butt welding joints were welded by the optimum wire feeding speed and the tensile strengths of those joints were evaluated. The mean value of tensile strengths of butt welding joints that were made using d.c.-pulsed GHTA welding with filler wire in vacuum was almost same value as that was welded by GTA (Gas Tungsten Arc) welding in air.
