Elucidating the distinct mechanisms of Er and Y in elevating the creep resistance of Al-Cu-Mg alloys

Abstract

The effects of Er and Y microalloying on the creep behavior of Al-Cu-Mg alloys were comparatively investigated in this work. Three T6-treated alloys, including Al-4Cu-0.25 Mg (as-received alloy), Al-4Cu-0.25 Mg-0.1Er (Er-modified alloy) and Al-4Cu-0.25 Mg-0.1Y (Y-modified alloy), were crept at 270 °C under applied stresses ranging from 100 MPa to 120 MPa. Both Er and Y significantly reduced the steady creep rate, with the Er-modified alloy exhibiting the greatest creep resistance, followed by the Y-modified alloy and then the as-received alloy. Microstructural analysis revealed that θ’-Al₂Cu and S′-Al₂CuMg precipitates significantly coarsened during creep, but the coarsening degree depended on alloy composition. Specifically, the Er-modified alloy exhibited the lowest coarsening rate, which was attributed to local Er enrichment at precipitates. The retained fine precipitates effectively hindered dislocation motion and sub-grain boundary migration, which contributed to the reduced steady creep rate. In contrast, Y was predominantly distributed in the Al matrix and offered inferior suppression of precipitate coarsening compared with Er. Thus, segregation strengthening is more conducive than solution strengthening, and Er microalloying is a more effective choice than Y for enhancing the high-temperature creep resistance of Al-Cu-Mg alloys.