MS-4-P-3136 Hf-containing precipitates in the Al-Si-Mg-Hf aluminum alloy

Hf element has the same group as Zr and Sc elements in the elemental table. For the latter two, there are many research reports because of their efficient effect on the alloy properties by adding a small amount of them. Particularly, co-addition of Zr and Sc could form core-shell structure which is more stable and homogeneous distributed comparing to either individual addition. However, fewer studies on Hf addition into aluminum alloys can be found. A new precipitate were reported by one of the present authors, which shows nanobelt-like morphology with Si2Hf structure [1].

In this work, different Hf-containing precipitates in Al-Si-Mg-Hf alloys were found. The precipitates show various kinds of morphologies, such as nanobelt-like, rectangle, triangle, trapezoid etc.(Figure 1) The chemical compositions and crystal structures of these precipitates were investigated by STEM-EDS and HRTEM with diffraction techniques. It was shown that the formation of the Al-Hf or the Si-Hf precipitate is closely related to the heat treatment conditions. The precipitates formed at high temperature of 560oC were investigated in more detail. The distribution and the orientation relationship of the nanobelt-like precipitate were studied by FIB 3D-imaging reconstruction combined with EBSD and HRTEM as well. In addition, the growth mechanism of the nanobelt-like precipitate preferentially along one-dimension will be discussed.

Keywords: Aluminum alloy, Precipitation, TEM, FIB

Reference:

[1] Z.H. Jia, L. Arnberg, Nanobelts in multicomponent aluminum alloys, Appl. Phys. Lett., 2008, 093115.