Microscopic phase field simulation of the retrogression-reaging (RRA) treatment on Al-Li alloys

Based on microscopic phase field dynamic diffusion equations with the discrete format, the aging heat treatment and three different retrogression-reaging (RRA) heat treatments to an Al-11.7at.%Li alloy were studied using computer simulation. Firstly, the aging heat treatment was carried out at 190°C to the alloy, then the retrogression was preformed in three different time steps at 360°C, among things for the retrogression in 33200 time steps there was full dissolution of δ′ (Al₃Li) and in 300000 time steps there was only partial δ′ in existence and in 200000 time steps there was partial dissolution of δ′. Follow on, the reaging heat treatments were conducted 190°C. The morphologies of precipitates δ′ phase were analyzed in qualitatively and quantitatively for above four simulations. The results shows that by RRA with full dissolution of δ′ the microstructure is the same as that by aging; by RRA with only partial δ′ in existence the optimum morphologies, i.e fime δ′ particle size and high particle concentration can be obtained; while the RRA with partial dissolution of δ′ leads to a few and larger particles.