Composition dependent thermal stability and evolution of solute clusters in Al-Mg-Si analyzed using atom probe tomography

Medium to high strength heat-treatable aluminum alloys of the 6000 series (Al-Mg-Si) have long been used for structural engineering applications. Their use in the automotive industry is growing rapidly, however the detrimental effects of room temperature storage (natural aging) on hardenability (artificial aging) hinders widespread applicability. Although numerous explanations have been proposed, there is no unified description of the mechanisms behind the negative effect. The current work builds on previous studies that identified a compositional (Mg:Si) dependence of the negative effect on hardening behavior, and finds a corresponding difference in the effect of room temperature clusters at artificial aging temperatures. Model alloys with different Mg:Si ratios were subjected to various thermal treatments including natural and artificial aging, and analyzed using atom probe tomography. This work represents the only atom probe tomography evidence to date showing increased thermal stability of naturally aged solute clusters in Mg-rich 6000 series alloys relative to Si-rich counterparts.