New Approach to Short-Range Ordering in GP(2) Zones in Al-3.82wt. % Cu Alloy

X-ray diffuse scatteing intensity measurement has been carried out for the Al-3,82% Cu single crystal in which GP (2) zones are found. The two dimensional equiintensity contour maps in h(1) h(2) 0 plane are obtained from surveying around several reflections. The diffuse intensity around 2 1 0 reflection, which shows a cross like streak, is carefully examined. Warren-Cowley short-range order parameters, a(i), are estimated from the diffuse intensities around 2 1 0 reflection. The component of the intensities coming from atomic displacements was subtracted from the total diffuse intensity. It is found that the equi-intensity contours after the correction of the atomic displacements shows an anisotropic distribution and the GP(2) zone is an ellipsoid with a modified layer structure.