Effect of Sc on microstructure and mechanical properties of as-cast Al-Mg alloys

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 alpha-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 alpha-Al phases rather than individual Al3Sc phase, which exhibited an 'Al3Sc + alpha-Al + Al3Sc.' multilayer structure. (c) 2015 Elsevier Ltd. All rights reserved.