Microscale Evaluation of Mechanical Properties and the Interfacial Microstructures of Friction Stir Welded Aluminum Alloy/Stainless Steel Dissimilar Lap Joints

The mechanical properties and interfacial microstructure of slices of friction stir welded aluminum alloy/stainless steel dissimilar lap joints were characterized. In an FSWed A3003 aluminum alloy/SUS304 steel lap joint, the strength on the advancing side was larger than that at the retreating side. TEM observation indicated that a sound joint that fractured at the base metal can be obtained from the stage of the formation of the amorphous layer owing to the mechanical alloying effects before the formation of intermetallic compounds. This lap joining technique was also successfully applied to A6061/T6 aluminum alloy-grooved SUS304 plates. Equiaxed aluminum grains were observed at the interface of the specimen after it was fractured, indicating that the interface deformed only slightly during the microtensile test. It was found that tensile strength of the joint was increased by aging at 433K, considering that precipitation occurred at this temperature. In addition, it was confirmed that the joint heated at 723K for 1.8ks still fractured at the aluminum matrix, assuming that intermetallic layers at the interface would slightly grow in this heating condition.