Abstract
The technological relevance of Al-Mg-Si alloys has been rapidly growing over the last decade. Of particular interest to current and future applications is the problematic negative effect of prior natural aging on subsequent artificial age hardening. The influence of natural aging is dependent on both processing and compositional variables and has origins that are far from well-understood. This work examines the hardenability of 6000 series alloys under a wide range of conditions, paying particular attention to the natural aging effect. Experimental variables include alloy composition (Mg + Si, Mg/Si), cooling rate after solutionization, and duration of prior natural aging. Hardenability was evaluated with full hardness and conductivity aging curves for each condition, as well as select Transmission Electron Microscopy (TEM). Results are discussed based on the actions of naturally aged solute clusters during artificial aging. In particular, a complex interaction between vacancy concentration, cluster stability, and precipitation driving force is suggested.
Highlights
Wrought aluminum alloys are currently of particular technological interest in the transportation industry due to their high strength to density ratio and relative ease of production
The results presented above can be qualitatively explained by considering concepts already published in the literature, and assuming a complex interaction between bulk composition and the various processes that occur during different thermal histories
In terms of solute atoms, natural aging (NA) clusters form by vacancy-aided diffusion; in terms of vacancies, some vacancies slowly annihilate at sinks, while others get trapped/immobilized in developing clusters as discussed in the Introduction
Summary
Wrought aluminum alloys are currently of particular technological interest in the transportation industry due to their high strength to density ratio and relative ease of production. For high strength engineering alloys, this period of intermittent storage, known as natural aging (NA), has long been known to have a detrimental effect on AA hardenability [3,4,5] This ‘negative NA effect’ is typically due to coarser distributions and/or lower volume fractions of strengthening precipitates [6,7,8,9,10,11,12,13,14], which is attributed to the prior formation of solute clusters during NA, and a multitude of suggested influences on the AA precipitation process [15,16,17,18,19,20,21,22]. Results are analyzed in accordance with the conceptual explanation discussed above ([19,40]), and highlight the importance of NA cluster thermal stability, quenched-in and trapped vacancy concentration, and precipitation driving force
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call