Preparation of millimeter scale second phase particles in aluminum alloys and determination of their mechanical properties

Abstract

The mechanical parameters such as elastic moduli E and shear moduli G of second phases are critical inputs for modeling and optimizing mechanical properties of aluminum alloys. However, some of these mechanical parameters are lacking because these micron or even nano scale phases are hard to be tested. The aim of this paper is to present an efficient approach to test the mechanical properties of second phases in aluminum alloys accurately. The α-AlFeSi, β-AlFeSi and Mg2Si particles at the millimeter scale were prepared by directional solidification with the aid of calculation of phase diagrams (CALPHAD). Such a large size can effectively reduce the impact of particle penetration into matrix in nanoindentation and Vickers hardness experiments. The elastic moduli of α-AlFeSi, β-AlFeSi and Mg2Si were determined as 183.81 ± 8.64 GPa, 174.13 ± 6.81 GPa and 116.38 ± 4.06 GPa, respectively, and their Vickers hardness values were 883 ± 64, 765 ± 21 and 475 ± 22 HV, respectively. Besides, the continuous uniform plastic deformation (without pop-in phenomenon in load-displacement curve) of Mg2Si was observed and is attributed to the anti fluorite structure of Mg2Si. Further, by Vickers hardness and electron backscatter diffraction (EBSD) it was found that the hexagonal α-AlFeSi had greater hardness anisotropy than the near-tetragonal β-AlFeSi. Overall, the hardness values of α-AlFeSi particles in <u 0u¯w> direction were higher than others, the hardness values of β-AlFeSi particles near <001> were lower than others.