Thermal Analysis of the Impact of RT Storage Time on the Strengthening of an Al-Mg-Si Alloy

Abstract

Despite the large number of papers dealing with the Al -Mg-Si system, the decomposition of the supersaturated solid solutions during the different aging treatments and therefore, the related hardening is still under debate. In the present work, by the use of simple techniques such as the Differential Scanning Calorimetry (DSC), Microhardness measurements and X-Ray Diffraction (XRD) analysis the precipitation behaviour and the impact of prior natural aging after homogenization on the subsequent microstructural and mechanical evolutions during artificial heat treatment at 160℃, of nuclear aluminium alloy Al-1.32% Mg-0.53% Si (% wt.) alloy, were identified. Through DSC, lattice parameter and microhardness measurements, the precipitation sequence were indirectly identified to be as follows: supersaturated solid solution (S.S.S.) → atomic clusters and GP zones →β” →β’ →β. The evolution of the mechanical properties during natural aging has been explained to be due to GP zones and atomic clusters formation. Storage at RT was found to have an important effect on the mechanical properties of the studied alloy. Under the light of the DSC results, this effect was explained by a slower precipitation kinetics of the β” phase; the atomic clusters and GP zones, which formed during storage at RT and the low concentration of the quenched-in vacancies in the stored samples have a delaying effect upon the nucleation of β” phase. Consequently, the final microstructure developed in these samples is coarse; hence lower mechanical properties are obtained.