Experimental and modelling assessment of ductility in a precipitation hardening AlMgScZr alloy

Abstract

Precipitation hardening is the most effective strategy to enhance the mechanical properties of metals. Dislocation mechanisms to control strengthening during precipitation have been demonstrated extensively. However, owing to the complexity of different precipitates in alloys, variations in ductility caused by precipitation are complex and have not been clarified so far. In this study, the effects of precipitation on ductility in precipitation hardening aluminium alloys are investigated based on a modified dislocation-based approach and experimental characterisation. The AlMgScZr alloy with spherical Al3(Sc, Zr) precipitates is used as a model alloy system to understand the effects of precipitation on ductility. Via heat treatment, shearable and nonshearable Al3(Sc, Zr) precipitates are introduced in the AlMg matrix. The results show that the ductility of AlMgScZr alloy decreases when shearable precipitates occur, while it increases with shearable precipitates being replaced by nonshearable precipitates. The variation in ductility of AlMgScZr alloy is mainly controlled by the dynamic recovery rate of the dislocations. Finally, by analysing the different precipitate-dislocation interactions and evaluating the dislocation density evolution during deformation, the dislocation mechanisms of 2 ductility during precipitation for AlMgScZr alloy are demonstrated. This study reveals the dislocation mechanism for controlling ductility during precipitation for AlMgScZr alloy which can provide a theoretical foundation for the design of high-performance structural materials.

The influence of shearable and nonshearable precipitates on the Portevin-Le Chatelier behavior in precipitation hardening AlMgScZr alloys

“…The quantitative information on Al3(Sc, Zr) (average radius and volume fraction) obtained by TEM and SANS is close to the previous results for the Al-Sc-Zr systems [Seidman et al, 2002;Fuller et al, 2003;Clouet et al, 2005;Marquis and Seidman, 2005;Deschamps et al, 2007;Knipling et al, 2010;Taendl et al, 2016]. It can be seen from Table 1 that the precipitate radius for AlMgScZr-623K/3h alloy is smaller than 3 nm (the critical radius between shearable and nonshearable precipitates is about 3-4 nm [Fazeli et al, 2008;Knipling et al, 2010;Lai et al, 2013;Okle et al, 2019;Chen et al, 2021], thus the precipitates in this alloy are defined as shearable precipitates. Analogously, the precipitates in AlMgScZr-773K/3h and AlMgScZr-813K/24h alloys are defined as nonshearable precipitates.…”

“…Here R1 is the critical radius between combined modulus-coherent strengthening and order strengthening; R2 is the critical radius between order strengthening (or shearing mechanism) and Orowan strengthening. According to previous studies [Fazeli et al, 2008;Knipling et al, 2010;Okle et al, 2019;Chen et al, 2021], R1≈1.2 nm and R2≈3-4 nm for Al-Sc-Zr alloy [Fazeli et al, 2008;Knipling et al, 2010Knipling et al, , 2011Lai et al, 2013;Luca et al, 2019;Okle et al, 2019]. Besides, we calculate the critical radius Rc, for the transition between the shearing and bypassing mechanisms, which according to reference [Bréchet and Louchet, 1990]:…”

“…The SANS experiment was performed on the SANS instrument at China Spallation Neutron Source (CSNS) [Ke et al, 2018]. The detailed information about SANS and data fitting process can be found in reference [Chen et al, 2021].…”

“…The well-known mechanisms between precipitates and dislocations are shearing (for shearable precipitates) and bypassing mechanisms (for nonshearable precipitates) [Ardell, 1985;Gladman, 1999;Knipling et al, 2010Knipling et al, , 2011Hull and Bacon, 2011;Fan et al, 2018;Ming et al, 2018;Barnett et al, 2019;Xu et al, 2019;Chen et al, 2021]. The influence of precipitates on the PLC behavior lies in revealing the mechanisms of appearance of precipitates on existing dislocation-dislocation and dislocation-solute interactions.…”

“…The shearable and nonshearable Al3(Sc, Zr) precipitates can be obtained through controlling heat treatment, and their quantitative characterization can be easily obtained by transmission electron microscopy (TEM) and small angle neutron scattering (SANS) techniques due to its good uniform dispersion, spherical shape and thermal stability [Fuller et al, 2003;Clouet et al, 2006;Voorhees, 2006;Deschamps et al, 2007;Deschamps and Geuser, 2011;Chen et al, 2021]. In this study, we focus our attention on effects of different dislocation-precipitate interactions (shearing and bypassing mechanisms) on PLC behavior including propagation behavior of PLC band without considering the variation of solute concentration, which has not been reported to our knowledge.…”