Microstructure Evolution and Interfacial Bonding Properties of Dissimilar T-Lap Joints Using Friction Stir Welding Parameters

The dissimilar aluminum alloys 5083 and 7075 were friction-stir-welded via a T-lap configuration under various welding speeds. The microstructure evolution in both the cross and longitudinal sections was revealed at the advancing side (AS), center, and retreating side (RS). The local bonding strength along the joint interface was assessed throughout the mini-specimens extracted from the original T-joints. The results indicated that the microstructure grain size and intermixing of the two alloys with periodic material flows gradually reduced from the RS to the AS sides. Increasing the welding speed reduced both the mixture of the two metals and the microstructure grain size. The role of the intermixing of the two alloys on the interfacial bonding strength was more important than that of the grain size. The highest bonding strength was reached at approximately 380 MPa for the RS produced at 50 mm/min. A mixture of the two alloys was found on the fracture surface using analyzing energy-dispersive x-ray spectroscopy. The fractography of interfacial bonding indicated that AA5083 exhibited ductile fracture behavior, while AA7075 showed brittle failure.