Abstract:Non-isothermal aging (NIA) is a composite heat treatment process that involves heating aging, cooling aging, and complex solute precipitation sequences. The precipitation behavior and the strengthening and toughening mechanisms of the 2014 Al alloy during NIA were studied by employing tensile, fatigue crack growth, hardness, and electronic conductivity tests, as well as high-resolution transmission electron microscopy and scanning electron microscopy. The results show that during NIA, the θ′ phase exhibits a complex process of nucleation, nucleation and growth, nucleation and growth and coarsening, growth and coarsening, nucleation and growth, and nucleation. NIA treatment imparts a mixed precipitation characteristic on the alloy, which is manifested as coherent precipitates, including GP zones, θ′′ phases, small-sized θ′ phases, and semi-coherent or non-coherent precipitates such as large-sized θ′ phases and equilibrium θ phases. The simultaneous strengthening and toughening of the NIA-treated 2014 Al alloy is caused by the synergistic effects of the particle-shearing mechanism and Orowan bypassing mechanism.

Key words: 2014 Al alloy; non-isothermal aging; precipitation behavior; strengthening and toughening