Microstructures evolution and localized properties variation of a thick friction stir welded CuCrZr alloy plate

The welding processing between large-dimension components is a big challenge for manufacturing in modern industry. In this work, a friction stir welding technology was employed to weld 30 mm thick CuCrZr alloy plates together with high strength and conductivity. The thermal histories and temperature distributions in the welded plate produced by friction stir welding (FSW) were simulated. The microstructural evolution and variation of properties in different regions around the weld line were investigated systematically. The results revealed that the large grains in the base material (BM) were transformed into a microstructure where the grains were completely equiaxed in the weld nugget zone (WNZ) induced by continuous dynamic recrystallization (CDRX), which can be attributed to the combination of severe deformation and high welding temperature. The significant changes to the heat gradient resulted in variations of prominent microstructures and properties in the structure from the top to the bottom layers in the WNZ. In the thickness direction, the exquiaxed grain size in the WNZ were decreased gradually while the hardness and strength were increased slightly. The large strength of the BM is due to the precipitation strengthening from the Cr precipitates even though the grain size is larger than that in the WNZ, while the large strength of the bottom layer is dominant because of the grain boundary strengthening.