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In this work, the effect of friction stir processing (FSP) on microstructure and mechanical properties of an Al-5Mg-0.2Sc-0.1Zr alloy was investigated in detail. The results showed that the as-cast alloy exhibited equiaxed grain structure with a large number of primary Al3(Sc,Zr) particles inside. FSP imposed a significant grain-refining effect on the alloy, changing the average grain size of 50.5 μm to 2.4 μm, which is attributed to the occurrence of dynamic recrystallization and generation of nanoscaled Al3(Sc,Zr) precipitates. These Al3(Sc,Zr) dispersoids intense impeded the movement of dislocation and grain boundaries and hindered the growth of recrystallized grains, resulting in a remarkable grain-refining strengthening, substructure strengthening and precipitation strengthening effect. On the other hand, the residual primary Al3(Sc,Zr) particles gave rise to a loss in ductility.

Friction-stir processing (FSP) imposed a remarkable grain refining effect on Al-5Mg-0.2Sc alloy, changing typical dendritic microstructure into fine and equiaxed recrystallized grains. Such effect was found to be related to intense plastic deformation and high-temperature exposure, resulting in occurrence of dynamic recrystallization. During this process, Al3Sc dispersoids due to the addition of 0.2 % Sc in a high density were precipitated and effectively hindered the migration of grain boundaries and subsequent grain growth, giving rise to a significant grain-refining strengthening effect. On the other hand, these Al3Sc precipitates caused an additional substructure strengthening and precipitation strengthening effect. An attractive comprehensive property of Al-5Mg-0.2Sc alloy subjected to FSP was obtained.

The effect of Sc on the microstructure and mechanical properties of Al–Si–Mg–Cu–Ti alloy was investigated. Results obtained in this research indicate that, with increasing Sc content, the microstru...

Primary particles with faceted cubic morphology were produced in as-cast Al-Mg alloy due to the addition of Sc. The cross-section of the particles revealed some eutectic structure composed of multilayer of ‘Al3Sc + α-Al + Al3Sc····’. At the cooling rate of 200 – 300 K/s, Al3Sc primary phase nucleated initially on oxides within the melt and developed to a cubic structure with a ‘cellular-dendritic’ mode of growth. The formation of α-Al structural shells was attributed as a reason for the segregation of Mg-rich lamellar dendrites at later stages. A growth mechanism for multilayer structure was proposed using the results presented.

Primary particles formed in as-cast Al-5Mg-0.6Sc alloy and their role in microstructure and mechanical properties of the alloy were investigated using optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD) and tensile testing. It was found that primary particles due to a close orientation to matrix could serve as the potent heterogeneous nucleation sites for α-Al during solidification and thus impose a remarkable grain refinement effect. Eutectic structure consisted of layer by layer of ‘Al 3 Sc + α-Al + Al 3 Sc + ⋯’ and cellular-dendritic substructure were simultaneously observed at the particles inside, indicating that these particles could be identified as the eutectics rather than individual Al 3 Sc phase. A calculating method, based on EBSD results, was introduced for the spatial distribution of these particles in matrix. The results showed that these eutectic particles randomly distributed in matrix. In addition, the formation of primary eutectic particles significant improved the strength of the Al-Mg alloy in as-cast condition, which is ascribed to the structural evolution from coarse dendrites to prefect fine equiaxed grains. On the other hand, these large-sized particles due to the tendency to act as the microcrack sources could cause a harmful effect in the ductility of Al-Mg-Sc alloy.

An addition of a high level of 0.6 wt% Sc imposed a remarkable grain refining effect on Al-5Mg alloy for as-cast condition, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the extensively formed Sc-rich particles. Electron back-scatter diffraction (EBSD), Atomic force microscopy (AFM) and SEM-elemental mapping were employed to investigate the inner structure of these particles and their role in grain refining. They could be identified as some eutectic structure consist of multilayer of ‘Al 3 Sc + α-Al+Al 3 Sc····’, which shows good consistency in orientation both in the particle and matrix.

The effect of Sc addition on microstructure and mechanical properties of as-cast Al–Mg alloys was investigated based on optical microscopy (OM), scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD) and properties testing. The results showed that a remarkable grain refining effect was observed for Sc content greater than 0.4 wt.%, changing typical dendritic microstructure into fine equiaxed grains. Such effect was found to be related to the formed primary particles, which hindered the undesirable diffusion and subsequent crystal growth and acted as potent heterogeneous nucleation sites for α-Al matrix during solidification. In addition, these particles could cause a significant refinement strengthening effect. Atomic force microscopy (AFM) and SEM-elemental mapping were employed to investigate the internal structure and elemental distribution of these particles. They could be identified as the eutectics consisted of Al3Sc and α-Al phases rather than individual Al3Sc phase, which exhibited an ‘Al3Sc + α-Al + Al3Sc⋯’ multilayer structure. Keywords: Al–Mg–Sc alloys, Grain refinement, Eutectics, Multilayer structure

In the present study, the effects of Mg, Cu, Sc and Zr combined additions on the microstructure and mechanical properties of hypoeutectic Al–Si cast alloy were systematically investigated. Characterization techniques such as optical microscopy (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), electron back-scatter diffraction (EBSD), atomic force microscopy (AFM), transmission electron microscope (TEM), Brinell hardness tester and universal testing machine were employed to analyze the microstructure and mechanical properties. The results showed that Sc served as modifier on the microstructure of Al–3Si–0.45Mg–0.45Cu–0.2Zr alloys, including modification of eutectic Si and grains. Extraordinarily, grain refinement was found to be related to the primary particles, which exhibited a close orientation to matrix. After T6 heat treatment, the grain structures were composed of nano-scaled secondary Al3(Sc, Zr) precipitates and spherical eutectic Si. Combined with T6 heat treatment, the highest hardness, yield strength, ultimate tensile strength and elongation were achieved in 0.56 wt.% Sc-modified alloy. Interestingly, the strength and ductility had a similar tendency. This paper demonstrated that combined additions of Mg, Cu, Sc and Zr could significantly improve the microstructure and performance of the hypoeutectic Al–Si cast alloy.