Microstructure and mechanical properties of similar and dissimilar joints of aluminium alloy and pure copper by friction stir welding

SummaryIn the present study, the microstructure and mechanical properties of similar and dissimilar friction stir welded joints of aluminium alloy (AlA) and pure copper (Cu) were evaluated at variable tool rotational speeds from 150 to 900rpm in steps of 150rpm at 60mm/min travel speed and constant tilt angle 2°. The interfacial microstructures of the joints were characterised by optical and scanning electron microscopy. The Al4Cu9, AlCu, Al2Cu and Al2Cu3 intermetallic compounds have been observed at the interface and stir zone region of dissimilar Al/Cu FSWed joints. Variation in the grain size was observed in the stir zone depending upon the heat input value. Axial force, traverse force and torque value were analysed with variation in tool rotational speed. Residual stresses were measured at the stir zone by X-ray diffraction technique. Maximum ultimate tensile strength of ∼75% of AlA strength for AlA–AlA joints has been obtained at 750rpm and for Cu–Cu joint tensile strength of ∼100% of tensile strength of Cu was obtained at 300rpm. However, for Cu–AlA joint when processed at 600rpm tool rotational speed achieved maximum ultimate tensile strength of ∼77% of AlA