Effect of Er additions on ambient and high-temperature strength of precipitation-strengthened Al–Zr–Sc–Si alloys

• Published in: Acta materialia Vol. 60; no. 8; pp. 3643 - 3654
• Main Authors: Booth-Morrison, Christopher, Seidman, David N., Dunand, David C.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.05.2012; Elsevier
• Subjects: Aluminum alloys; Applied sciences; Erbium; Exact sciences and technology; Metals. Metallurgy; Precipitation; Scandium; Zirconium; Aluminum alloys; Precipitation; Zirconium; Erbium; Scandium; Lanthanide; Temperature; Aluminium base alloys; Composition effect; High temperature; Precipitation hardening; High temperature strength; Microstructure; Strength
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2012.02.030

The effect of substituting 0.01 at.% Er for Sc in an Al–0.06Zr–0.06Sc–0.04Si (at.%) alloy subjected to a two-stage aging treatment (4h/300°C and 8h/425°C) is assessed to determine the viability of dilute Al–Si–Zr–Sc–Er alloys for creep applications. Upon aging, coherent, 2–3nm radius, L12-ordered, trialuminide precipitates are created, consisting of an Er- and Sc-enriched core and a Zr-enriched shell; Si partitions to the precipitates without preference for the core or the shell. The Er substitution significantly improves the resistance of the alloy to dislocation creep at 400°C, increasing the threshold stress from 7 to 10MPa. Upon further aging under an applied stress for 1045h at 400°C, the precipitates grow modestly to a radius of 5–10nm, and the threshold stress increases further to 14MPa. These chemical and size effects on the threshold stress are in qualitative agreement with the predictions of a recent model, which considers the attractive interaction force between mismatching, coherent precipitates and dislocations that climb over them. Micron-size, intra- and intergranular, blocky Al3Er precipitates are also present, indicating that the solid solubility of Er in Al is exceeded, leading to a finer-grained microstructure, which results in diffusional creep at low stresses.