Disclosing differential precipitation behavior of a novel high Mg-containing Al-Mg-Zn-Si alloy

• A novel high Mg-containing Al-Mg-Zn-Si alloy (Mg is 8.7 wt%) is proposed. • Energetically favorable substitution of Al by Si induced GP T’ zone precipitation facilitate fine and dense T’ phase. • η’ phase is transformed from T’ phase or evolved from GPII η’ zone along grain boundary. • Differential precipitation of T’ phase and T’ + η’ phases simultaneously occur in the matrix and adjacent to grain boundary. The application of traditional Al-Mg-Zn alloy in aerospace field is limited due to poor corrosion resistance for β-phase at grain boundaries and low strength for the lack of T phase. Here we propose a novel high Mg-containing Al-Mg-Zn-Si alloy with a novel alloying strategy of high Mg content combining with a suitable microalloying Si, obtaining small and densely precipitated nanoscale T’ phase in the matrix, co-existing T’ and η’ phases adjacent to grain boundary and T phase at grain boundary. The formation of GP T’ zone in the matrix is dramatically enhanced due to energetically favorable substitution of Al by Si and furtherly facilitates homogeneous growth of T’ phase by solute redistribution. η’ phase is transformed from T’ phase or evolved from GPII η’ zone along grain boundary due to feasible thermodynamic condition of Mg-poor and Zn-rich domain by distinct Mg and Zn exsolution on grain boundary. The present alloying design makes it possible that differential precipitation behavior of T’ phase and T’ + η’ phases can simultaneously occur in the matrix and adjacent to grain boundary, the alloy has obviously advantaged overall performance over traditional Al-Zn-Mg-(Cu) alloys, which raises a new perspective for developing new high-performance lightweight aluminum alloys.