Developing a high-performance Al–Mg–Si–Sn–Sc alloy for essential room-temperature storage after quenching: aging regime design and micromechanisms

Abstract

Sn microalloying can depress the adverse effect of natural aging after quenching (i.e., room-temperature storage) of Al–Mg–Si alloys. However, the other effect of Sc micro-addition to the Al–Mg–Si–Sn alloys remains elusive. Here, the optimal room-temperature storage time, properties and micromechanisms of Al–0.43 Mg–1.2Si–0.1Sn–0.1Sc (wt%) alloy are investigated by atomic-resolution scanning transmission electron microscopy (STEM), microhardness and corrosion resistance tests. The results show that the peak-aging Al–Mg–Si–Sn–Sc alloy exhibits vastly shortened peak hardening time, increased thermal stability and corrosion resistance compared with its Sc-free counterpart after a long room-temperature storage time of 1 week. Under such a designed double-stage aging regime (1-week room-temperature storage + artificial aging at 180 °C), the addition of Sc to Al–Mg–Si–Sn alloy induces a decrease in diameter but an increase in length of peak-hardening β”-based precipitates. In addition, a suppressed over-aging phase transition from Sc/Sn-containing β” to β’ is identified in the Al–Mg–Si–Sn–Sc alloy. The Sn tends to segregate to the Si site in the low-density cylinder of β” and the central site of sub-B' in the precipitate can be occupied by Sn/Sc. Further study reveals that Sc and Sn coexist in the precursors of β”. Both reduced width of precipitation free zones and protective corrosion product film easily formed on the material contribute to the improved corrosion resistance of Al–Mg–Si–Sn–Sc alloy. The results provide important insight into the development of high-performance Al alloys. Graphical abstract: [Figure not available: see fulltext.].