Manufacturing of high-toughness Al–Si alloy by rolling and friction stir processing: Effect of traverse speed

Abstract

In this work, the influence of traverse speed on the microstructural evolution and mechanical behavior of Al–7Si alloy fabricated by cold rolling and friction stir processing (FSP) was studied. After the FSP, the needle-shaped silicon and Fe-rich phases were modified to fine particles with a low aspect ratio and high sphericity, and porosity was eliminated. The FSPed samples revealed a uniform dispersion of Si and Fe-rich particles in the aluminum matrix. With the increment of the traverse speed, the average size and sphericity of the Si particles were reduced, while the aspect ratio was increased. The peaks of α-Al, Si, Al 4 FeSi 2 , and Al 5 FeSi phases were observed in all samples, however, the Mg 2 Si peak was not visible due to its low content. With increasing the traverse speed, the peak shifting and lattice strain were decreased due to decreasing the degree of plastic deformation. The as-cast sample had an average hardness higher than the FSPed samples owing to the presence of large second phases. By performing the FSP, the tensile properties were significantly improved owing to the refinement, spheroidization, and uniform distribution of particles. Increasing the tool traverse speed up to 120 mm/min enhanced the strength of the FSPed samples because of decreasing the size of silicon and Fe-rich particles. Further increment of the traverse speed led to a decrease in the strength owing to the presence of cavities. The best strength-ductility belongs to the traverse speed of 120 mm/min which resulted in the highest toughness (57.9 J/cm 3 ). The ductile fracture was the dominant feature on the fracture surface of all FSPed samples.