Microstructures and thermal stability of the semi-solid 2024 aluminum alloy prepared using the pulsed magnetic field process: Effects of technological parameters

A novel technique for introducing pulsed magnetic field (PMF) during solidification of 2024 aluminum alloy has been employed for preparing semi-solid feedstock reheated into semi-solid state for partial remelting. The effects of different process and technological parameters, such as pouring temperature, discharging frequency, heating temperature, and holding time, on the semi-solid microstructures during partial remelting were investigated. The results showed that the primary α-Al particles in semi-solid feedstock became much finer and rounder with decreasing pouring temperature and/or increasing discharging frequency. However, over a certain discharging frequency, coarse structures appeared again. A thixotropic microstructure liable to form semi-solid alloy was obtained if the feedstock was reheated at 620 °C for 30 min. Under such conditions, the average diameter was 146 μm and the average shape factor was 0.78. The coarsening was analyzed by Lifshitz–Slyozov–Wagner (LSW) theory. Based on the experimental data on grain growth obtained by partial remelting, the coarsening rate constant, K, was figured out. The K for the investigated alloy was compared with that for other alloys processed by different method, and analyzed in relation to those reported in previous literature.

► Feedstock became finer and rounder with the decrease of pouring temperature.
► Feedstock became finer and rounder with the increase of discharging frequency.
► Coarse structures appeared again over a certain discharging frequency.
► The optimal partial remelting parameters should be 620 °C and 30 min.
► The feedstock prepared by PMF process exhibited a higher thermal stability.