Abstract:The non-uniform microstructure and high temperature coordinated deformation behavior of friction stir butt-welded 2A97/5A06 dissimilar aluminum alloy plate were studied. The microstructure of each zone in the welded joint was observed, and the high temperature mechanical properties of both individual zones and the whole joint were studied. Results show that grains in the weld nugget zone of 2A97 and 5A06 are fine. The grain sizes of various zones on the 2A97 side are small and uniform, whereas those on the 5A06 side are slightly larger and exhibits a more significant variation. Under the condition of 430 °C and 10–3 s–1, the 2A97 and 5A06 base metals exhibit good high temperature properties, with elongations reaching 278.8% and 120.6%, respectively. The strength and elongation of the nugget zone in the joint are 18.4 MPa and 176.1%, respectively, which are between those of 2A97 and 5A06 base metals. The strength is about 2 times higher than that of the 2A97 base metal, and the elongation is about 1.5 times higher than that of the 5A06 base metal. The overall performance follows superposition principle. Due to the varying deformation resistance of each region, fracture occurs in the thermo-mechanically affected zone on the 2A97 side after concentrated deformation during transverse tensile testing. After correction, the flow stress is slightly higher than that of the base metal and the elongation is close to that of the base metal. The grain size and flow stress of each region after welding follow the creep equation. The smaller the grain size, the lower the flow stress.