Structural changes in age- hardenable aluminium alloys induced by low temperature neutron irradiation

In order to investigate the structural changes in alloys with different size and structure of small spherical G.P. zones and intermediate precipitates, measurement of X-ray small angle scattering were carried out at liquid nitrogen temperature for A1–4.4 at per cent Zn, AI-1.0 at per cent Ag, AI-5.0 at per cent Zn-5.0 at per cent Ag and AI-2.8 at per cent Zn-1.4 at per cent Mg alloys. Through the measurement of the scattering intensities before and after irradiation with doses of 3.2 ×1015 and 1.5 × 1016 n· cm−2 below 20 °K, the changes in size, volume fraction and size distribution were clearly detected. The Guinier radius decreased with irradiation for all of the specimens. The Porod radius of G.P. zones in the binary alloys also decreased, except the Al-Zn alloy containing small G.P. zones with short spacing. The integrated intensity, which is proportional to the volume fraction, slightly decreased for the binary alloys, and increased for the ternary alloys. The size distribution after irradiation became wider for the specimens containing G.P. zones or precipitates with short spacing, but narrower for the ones with long spacing of G.P. zones and low concentration of solutes in matrix. This behaviour is explained by the mechanism of breaking of small spherical G.P. zones and precipitates by collision cascades and displacement spikes during low temperature irradiation.