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The surface topography of friction stir welding (FSW) plays an important role in the performance of joints. In this paper, the principle of surface texture of FSW was investigated in detail. The AA7075 aluminum alloy was friction stir welded at different rotational speeds and welding speeds, and the effect of process parameters on the surface topography was studied. The fractal dimension of the surface topography was calculated using the pixel-covering method. Moreover, the relationship between the surface topography and the fractal dimension was obtained. The results show that the surface arc texture spacing becomes smaller with the increase of the rotational speed and larger with the increase of the welding speed. There is a corresponding relationship between the fractal dimension of the surface topography and the surface roughness. The larger the surface roughness is, the larger the fractal dimension is. [ABSTRACT FROM AUTHOR]

In the paper, the disc sheet of 2024 aluminum alloy was shaped precisely into a flat-bottom cup by two stage laser shocking, and its microstructure evolution was studied by Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) in detail. The investigations show that the grains are elongated and continuously refined by continuous dynamic recrystallization during two stage laser shock sheet forming (TSLSSF). With the increase of strain of metal sheet, the transformation from low-angle grain boundaries and high dislocation densities to high-angle grain boundaries and low dislocation densities occurs, which improves the strength and plasticity of the processed material in comparison with the untreated material. The impact affects significantly the texture evolution process of aluminum alloy sheet under two stage forming. After laser shocking, the textures of the aluminum alloy sheet tend to be stabilized at the β-Fiber and a strong P texture is also formed. Due to the combined effect of grain size and dislocation density, the hardness of the second impact material increases less than that of the first impact. The research provides a reference for the application and development of laser shock forming. • The microstructure evolution of the material after laser shocks was characterized. • The proportion of low-angle grain boundaries first rises and then falls. • The ratio of dislocation density first enhances and then drops after laser shocks. • The textures of the sheet are inclined to be stabilized at β-Fiber and P component. • The hardness increase after the second impact is less than that after the first. [ABSTRACT FROM AUTHOR]