Enhanced creep performance in an Al–Cu–Mg–Ag alloy through underageing

• Published in: Acta materialia Vol. 50; no. 14; pp. 3597 - 3608
• Main Authors: Lumley, R.N., Morton, A.J., Polmear, I.J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 16.08.2002; Elsevier Science
• Subjects: Age hardening; Aluminium alloys; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Creep; Dynamic precipitation; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Mechanical properties of solids; Metals. Metallurgy; Physics; Dynamic precipitation; Creep; Aluminium alloys; Age hardening; Magnesium additions; Binary alloys; Precipitation; Aluminium base alloys; Creep curve; Copper alloys; Mechanical properties; Creep strength; Silver additions; Experimental study
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/S1359-6454(02)00164-7

Tests at 130 °C and 150 °C have shown that the creep resistance of an Al–Cu–Mg–Ag alloy is significantly increased if it is heat-treated at an elevated temperature to an underaged condition rather than the fully hardened, T6 temper. This beneficial effect of underageing is manifest in reduced rates of secondary creep. Similar results have been obtained for the commercial alloy 2024. Delays at ambient temperature after underageing and before testing lead to secondary precipitation and a progressive decrease in creep performance that eventually reverts to close to that for the T6 condition. This detrimental effect may be overcome by slow cooling from the underageing temperature, which arrests or impedes subsequent secondary precipitation. Microstructural observations suggest that the enhanced creep resistance in the underaged condition is a consequence of the presence of “free” solute in solid solution that is not yet involved in precipitation.