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

STUDY OF PRECIPITATION KINETICS OF AN Al-Mg-Si ALLOY USING DIFFERENTIAL SCANNING CALORIMETRY

“…2) shows three exothermic peaks which correspond to the formation of β″ (peak 2′), β′ (peak 4′) and β (peak 6′), and four endothermic peaks (1′, 3′, 5′ and 7′) which correspond to the dissolution of GP zones, the metastable phase β″, β′ and the stable phase β respectively. These peaks observed in the Al-Mg-Si alloy (quenched and aged at room temperature for three weeks) are similar to those published in the literature on similar alloys [11,12]. We can deduce that during the natural aging of Al-Mg-Si alloy, the GP zones form, but during heating in the DSC instrument, the first thing that happens is the dissolution of these particles (peak A) [13,14].…”

The Natural Aging Effect on the Activation Energy of the Precipitation Processes in the Al-Mg-Si Alloy

“…Each sample was processed with three different heating rates (10, 20 and 30°C/ min) from room temperature to 550°C in N 2 atmosphere. These peaks observed in the alloy aged at RT are similar to those published in the literature on similar alloys [12,13]. We can deduce that during the natural aging of Al-Mg-Si alloy, the GPzones form, but during heating in the DSC instrument, the first thing that happens is the dissolution of these particles (peak A) [14,15].…”

“…Thus, the transportation of the Mg and Si atoms from the clusters and the solid solution to β″ nuclei will be much slower during natural aging. This reduced diffusion delays the formation of β″ particles [12].…”

Clustering and Precipitation during Early-Stage Artificial Aging of Al–Si–Mg(–Cu) Foundry Alloys

“…This was recently confirmed with kinetic Monte Carlo simulations [25]. The non-nucleating clusters predominantly form during RT storage in dense alloys and are responsible for the negative effect on hardness after AA [10,26]. The effect has been found to be large in Mg-rich alloys, but more subtle in Si-rich alloys [15,27], which are the object of this paper.…”