J. Mater. Sci. Technol. ›› 2021, Vol. 67: 186-196.DOI: 10.1016/j.jmst.2020.06.032

• Research article • Previous Articles     Next Articles

Investigation of the 12 orientations variants of nanoscale Al precipitates in eutectic Si of Al-7Si-0.6Mg alloy

Yifan Wang, Yanli Lu*(), Jing Zhang, Wenchao Yang, Changlin Yang, Pan Wang, Xiaoqing Song, Zheng Chen   

  1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, YouyiXi Road 127, Xi’an, 710072, China
  • Received:2020-04-16 Revised:2020-05-23 Accepted:2020-06-01 Published:2021-03-20 Online:2021-04-15
  • Contact: Yanli Lu
  • About author:* E-mail address: luyanli@nwpu.edu.cn (Y. Lu).

Abstract:

Various orientations and diffraction patterns from nanoscale Al precipitates in eutectic Si were investigated by high-resolution transmission electron microscopy combined with transition matrix and stereographic projection. It was found that the Al precipitates had 12 variants, all orientation relationships can be expressed as: (001)Al//{111}Si, [110]Al//<$\bar{1}10$>Si. Further, a new diffraction pattern model from Al precipitates was established under [111]Si zone axis, which was in good agreement with the experiment data. The microstructure, adhesion strength and electronic structure of the interface between Al precipitate and Si matrix were studied by first-principles calculation and experimental observation. The results show that the covalent bonds are formed between interfacial Al and Si atoms, which play a key role in interfacial bind strength. Based on the Griffith fracture theory, the cracks tend to form and expand in the interior of Al precipitates firstly, and the interfaces can act as a protective layer to prevent crack propagation. Therefore, the nanoscale Al precipitates will improve the toughness of eutectic Si particles by releasing part of stress through lattice distortion. In addition, the stretched nanoscale Al precipitates can act as effective heterogeneous nucleation sites for high density deformation nanotwins in eutectic Si during deformation, which significantly improved the deformability of eutectic Si.

Key words: Aluminum precipitates, Silicon particles, High-resolution transmission electron microscopy, Strengthening mechanism, First-principles