Behavior of microstructure evolution of ZL205A cast aluminum alloy during semi-solid isothermal annealing process

The behavior of microstructure evolution of ZL205A aluminum cast alloy during semi-solid heat-treatment process for different holding time was studied. It was found that the relationship between the average diameter of α(Al) grains and the isothermal holding time fit the formula r̄³-r̄₀³ = k′·t, where the constant k′ varied with the holding temperature, which is equal to 4.288 × 10^-10 m³/s and 5.962 × 10^-10 m³/s at 622°C and 631°C, respectively. The semi-solid isothermal annealing process of experimental alloy can be divided into three stages, i.e. preparation stage, spheroidization stage and coarsen stage. A higher holding temperature could accelerate spheroidization of α (Al). The microstructure evolution of the alloy is attributed the result of the diffusion of the solutes as well as vacancies, and the grain boundary tension. The diffusion of the solutes plays a leading role in the preparation stage, and the grain boundary tension dominates the late stages, e.g. spheroidization stage and coarsen stage.