CORROSION AND PROTECTION OF FRICTION STIR WELDS IN AEROSPACE ALUMINIUM ALLOYS

Friction stir welding [1] (FSW) offers the opportunity of obtain-ing high quality welds in the traditionally poorly weldable high strength aluminium alloys of the 2XXX and 7XXX series. Due to the excellent quality of the welded joints, aircraft manufactures are considering the introduction of this technology in aircraft components. Friction stir welding has been used with success in joining primary structures in the Eclipse 500™ jet [2], and will be applied to join external fuel tanks in the NASA Space Shuttle [3]. A review of recent investigations on the properties of FSW has been compiled by Mishra and Ma. [4]. The corrosion performance of the welds has been analysed in a number of studies, which show that the thermal cycle produced by welding leads to significant changes in the microstructure of the metal, leading to enhanced corrosion susceptibility [5-24]. In aerospace alloys of the 2XXX and 7XXX series, this causes con-cerns related to the corrosion-fatigue of FSW components, as the onset of localised corrosion in aluminium alloys is known to be able to decrease this parameter (e.g. [25]). Recent work on AA2024 T351 [16, 17] showed the correlation between welding parameters and precipitation of the age-S phase, while for 7XXX