Study on microstructure, tensile performance and creep resistance of Al–Mg–Si-Sc-Zr alloy strengthened by Al3(Sc, Zr) nanoprecipitates

Abstract

In this work, a newly designed Al–Mg–Si-Sc-Zr alloy with both excellent room-temperature tensile performances and high-temperature creep resistance was prepared. The microstructure of Al–Mg–Si matrix alloy was significantly modified by Sc, Zr micro-alloying. The average grain size of Al–Mg–Si-Sc-Zr alloy in as-cast and as-rolled states was 68.3 μm and 7.33 μm respectively, which was far smaller than those of Al–Mg–Si alloy. Numerous Ll2-ordered Al3(Sc, Zr) nanoprecipitates ranging from 20 to 60 nm were generated during heat treatment, and they had a strong coherent interface relation with α-Al matrix. During rolling deformation, a further DRX (dynamic recrystallization) progress happened in Al–Mg–Si-Sc-Zr alloy due to the severe dislocations pile-up caused by Al3(Sc, Zr) nanoprecipitates. The YS (yield strength), UTS (ultimate tensile strength) and EL (elongation) of as-rolled Al–Mg–Si-Sc-Zr alloy at room temperature were 315.2 MPa, 372.3 MPa and 20.1 % respectively, which were increased by 21.9 %, 17.1 % and 41.5 % compared to tensile performances of Al–Mg–Si matrix alloy. An enhanced high-temperature creep resistance was obtained by Al–Mg–Si-Sc-Zr alloy, which was mainly attributed to the outstanding thermal stability possessed by Al3(Sc, Zr) nanoprecipitates. The strengthening mechanisms including grain refinement strengthening and Orowan strengthening were also discussed.