Microscopic Phase Field Simulation Of Aging-Reaging And Retrogression-Reaging On Al-Li Alloys

The microstructure evolution of Al-Li alloys during aging, aging-reaging and retrogression-reaging were simulated using microscopic phase field method. The computation program based on the diffusion equation with the discrete form and nonequilibrium free energy was designed to describe the course of aging, such as atomic clustering, ordering, growth, coarsening and so on. Atomic pictures, ordering parameters, particle size distribution and volume fraction of precipitates were obtained and analyzed.Compared with aging results, the particle density of precipitates is higher and the averaged particle size is smaller in the course of aging-reaging. The particle size distribution curve shows that precipitates diameter varies in a smaller extent, and the peak position of curve corresponding value locates on the small side of size, and the quantity of small sized precipitates is in the majority, especially to low concentration (Al-8.7at.%Li) and high concentration (Al-14.5at.%Li) alloy. Volume fraction of precipitates of aging-reaging of low concentrated alloy is on the small side of value of equilibrium phase. For the alloys of lower concentration and higher concentration, both the first aging temperatures and the reaging temperatures were performed at the same region of Al-Li phase diagram, respectively belong to metastable region and instable region, the first aging at the lower temperature of aging-reaging treatments can result in better morphology. For the alloy of medium concentration (Al-11.7at.%Li), the first aging temperatures were performed at instable region and the reaging temperatures were performed at transition region which between metastable region and instable region, the morphologies of the different first aging temperatures are almost same. For aging-reaging treatment, the difference of particle density and averaged size increase, the reaging time has a more and more small change to the size distribution curve of precipitates, as the Li composition increasing.Compared with aging results, with completely retrogression and reaging, the high concentration alloy can make particle density higher and particle size smaller, the particle size distribution curve shows that diameter of precipitates varies in a smaller extent and...