Natural Aging in Al-Mg-Si Alloys - A Process of Unexpected Complexity

• Published in: Advanced engineering materials 2010-07, Vol.12 (7), p.559-571
• Main Authors: Banhart, John, Chang, Cynthia Sin Ting, Liang, Zeqin, Wanderka, Nelia, Lay, Matthew D. H., Hill, Anita J.
• Format: Article
• Language: English
• Subjects: Aging (artificial); Aging (natural); Alloys; Aluminum base alloys; Atom probe analysis; Dynamics; Microscopy; Positrons
• ISSN: 1438-1656; 1527-2648; 1527-2648
• DOI: 10.1002/adem.201000041

The natural aging behavior of pure ternary Al‐Mg‐Si alloys is investigated by measuring hardness, electrical resistivity and positron lifetime, as well as carrying out thermal analysis and atom probe microscopy. It is found that several distinct temporal stages of natural aging can be distinguished in which one of these quantities shows a characteristic behavior and that these times coincide for many of these measurements. The rate of change in the measured data is correlated with proposed solute dynamics during natural aging for both aging that takes place prior to artificial aging (natural pre‐aging) and after artificial underaging (natural secondary aging) heat treatments. Controlling factors for solute dynamics are discussed. Pure Al‐Mg‐Si alloys are naturally aged after solutionizing and quenching. Measurements of hardness, electrical resistivity, positron lifetime, thermoanalysis, and atom probe tomography suggest at least four different stages of solute and vacancy clustering and early precipitation. The observed correlations between natural pre‐aging, artificial aging, and secondary aging allow for the discussion of solute dynamics in these alloys.