A New Spot Welding Technique for Fuselage

High strength aluminum alloys(series 2XXX and 7XXX)are kinds of precipitation-hardening alloys,which have been widely applied in manufacturing of fuselage for their high strength-to-weight ratio,good fatigue performance and damage tolerance[1-2].These structures mostly adopt lap joint.The traditional joining methods include riveting and bolting,which cost weight-increase and inefficiency.These disadvantages could be overcome by a new joining technique—friction stir spot welding(FSSW)developed from friction stir welding(FSW).However,after wel-ding,FSSW normally leaves the workpiece with a keyhole,which decreases mechanical properties and corrosion resistance of the joint.To fill the keyhole,refill friction stir spot welding(RFSSW,Refill-FSSW)was invented by GKSS in 1999.GKSS designs a special welding tool for RFSSW,consisting of pin,sleeve and clamping ring,which are precisely assembled with indepen-dent driving systems[3].In a typical RFSSW process,the pin and sleeve move in opposite direction at a given speed ratio.Approximately,the speeds are set inverse proportional to their cross-sectional area.In 2011,GKSS performed RFSSW on aluminum alloy and obtained the joint with good strength.Thereafter,RFSSW was highlighted in research,which was expected to apply in fuselage manufacturing and to replace the traditional joining methods.