Microstructural evolution and aging behavior of multicomponent Al–Sn–Zn–Mg–Li alloy

We investigate the microstructural characteristics and precipitation behavior of a multicomponent Al–Sn–Zn–Mg–Li alloy subjected to solution and aging heat treatments, to provide insights into the alloy design of precipitation-strengthened Al–Sn alloys. Solution treatment at 450 °C causes liquefication of the secondary phase (Mg₂Sn, Sn(Zn), and AlLi), forming a spherical Sn-rich phase composed of Sn, Mg₂Sn/Mg₉Sn₅, and Zn phases. Slow furnace cooling (FC) after solution treatment homogenizes the Sn-rich phase and forms coarse Zn precipitates in the Al matrix, producing coarser (∼5 nm) and fewer Zn-rich solute clusters during natural aging (NA). NA of water-quenched (WQ) alloys induces the formation of fine (∼2 nm) Zn-rich clusters (precursor of Zn) and Zn/Mg/Li clusters (precursor of Mg₂Zn₁₁) with an average chemical composition of 78.6Al–19.0Zn–1.6Mg–0.8Li (at%), resulting in age-hardening that is superior to that of the FC alloy. Artificial aging (AA) at 90 °C results in the formation of two types of precipitates (major plate-like MgZn₂-type lying on {111}_Al and minor blocky Mg₂Zn₁₁-type), which have lesser hardening effects than the Zn-rich clusters formed during NA. Zn-rich clusters formed during NA improve the hardness of the AA alloys at 90 °C, indicating the beneficial effect of NA at service temperatures. The precipitation-strengthening mechanism of the multicomponent Al–Sn alloy is further discussed based on theoretical strength modeling and analysis precipitate-dislocation interactions.