Investigations on the Precipitation in Monocrystalline Al-Mg-Si Model Alloy by Small Angle Neutron Scattering

Abstract

The aim of this work is to clarify the difference in anisotropic precipitate growth in an Al-Mg-Si single crystal during artificial ageing (AA) after different natural pre-ageing (NA) conditions. In one experimental series, in-situ small angle neutron scattering (SANS) experiments were performed at 180 degrees C right after solution heat treatment and quenching. In another series, the crystal was first naturally aged at `room temperature' for 1 week before AA, after which SANS experiment was carried out. The measurements were performed at D22 of the Institut Laue-Langevin with the single crystal mounted so that the neutron beam was parallel to one of the {001}(Al) directions. Anisotropic scattering from the needle-like precipitates growing along {001}(Al) was observed. The size evolution of the precipitates is compared for the crystal aged with and without NA. For this crystal without NA, the length of the precipitates increases significantly in the first 2h of AA. After this both the length and radius increase with AA time. With NA before AA, the number density of the precipitates is lower comparing to the directly AA crystal. The rate of increase in length of beta `' is lower and the mean size of beta `' is smaller.