Microstructural changes at the initial stage of precipitation in an aluminum-silicon alloy

In this study, we use a transmission electron microscope (TEM) to observe the microstructure of an Al-Si alloy from immediately after quenching to the initial stage of precipitation. Results reveal the presence of patches immediately after quenching that are thought to be Si clusters, and these are coherent with the {111}_matrix. At the initial stage of aging, Si crystals with a plate-like structure are observed, contradicting the round shape previously described. We propose that the Si clusters that appear immediately after quenching act as nuclei for the plate-like Si crystals. As the aging time increases, these increase in length and thickness, becoming thick plate-like Si phase precipitates.