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The microstructure and phase constituents in stir zone of friction stir weld for 2024-T4 aluminium alloys were observed and analysed by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction analysis. Homogeneous amorphous structure in some area of the weld nugget zone was detected. The amorphous structure with halo pattern has a structure characteristic of the long-range disorder. X-ray diffraction analysis indicated that a diffuse scattering peak in the shape of steamed bun with amorphous characteristic exists in the degree scope of 15 • -29 • . Some influencing factors, such as higher temperature gradient, hydrostatic pressure and shear stress and strain, may induce the formation of amorphous structure in weld nugget zone of friction stir weld. K e y w o r d s : friction stir welding, amorphous structure, transmission electron microscopy, X-ray diffraction, microstructure