The Natural Aging Effect on Hardenability in Al-Mg-Si: A Complex Interaction between Composition and Heat Treatment Parameters

• Main Authors: Alex Poznak, Violet Thole, Paul Sanders
• Format: Article
• Language: English
• Published: MDPI AG 2018-05-01
• Series: Metals
• Subjects: aluminum alloys; Al-Mg-Si; precipitation strengthening; solute clustering; natural aging; artificial aging; quench sensitivity; hardness; conductivity; transmission electron microscopy
• Online Access: http://www.mdpi.com/2075-4701/8/5/309

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.