Shape anisotropy of GP zone in early decomposition process of Al-Zn binary alloy

The structural anisotropy of GP zone in an Al-Zn binary alloy has been investigated using in situ small angle X-ray scattering measurement with a synchrotron radiation source. As a result, 2-dimensional images of scattering intensity showed the orientation dependence. The maxima of scattering intensities were observed along the [001] directions. In the high scattering vector range, the contour of scattering intensities also showed anisotropy and the form for the early stage of aging was different from that for the late stage. The difference among each Guinier radii determined from one dimensional profile along the [001], [110] and <111> directions predicted a facetting for the {111} interface of GP zone. Assuming the form of GP zone is faceted sphere, we calculated the structure factors. The result agreed with the experiments in the range, where the scattering intensity gives information on the shape of small precipitates like GP zone.