Prediction and identification of calcium-rich phases in Al–Si alloys by electron backscatter diffraction EBSD/SEM

Abstract

Al–7Si–3Cu–Fe, Al–7Si–3Cu–Fe–0.5Mn, Al–12Si–Mg–Ni–Cu, A319 and A380 alloys containing 0.0020, 0.0040, 0.0080, 0.1 and 0.2 wt.% Ca were used in this research to study the effects of Ca additions on their microstructures and hardness. Samples from the molten alloys were taken and characterized by SEM, EDS and EBSD analysis. Electron backscatter diffraction patterns (EBSDPs) were used to assess the crystallographic characteristics of calcium compounds, thus identifying their stoichiometry. On the other hand, microstructural formation was predicted using an adapted version of Thermo-Calc™ software. Compounds which contain calcium-rich particles with “needle-like” or “plate-like” morphologies were consistent with that of the hexagonal CaAl 2Si 2 intermetallic phase in all of the alloys used. Moreover, it was found that Ca additions of 40 ppm and higher, refined the eutectic Si particles and coarsened the iron-rich intermetallics as well. Brinell hardness was evaluated to determine the effect of calcium concentration on the hardness of the Al–Si alloys used in this study.