The influence of adding trace of La/Ce on the as-cast microstructure, precipitation behavior and thermodynamic properties of A356.2 alloy was systematically investigated by means of metallographic observation, transmission electron microscopy, differential scanning calorimetry among others. The results show that adding trace of La or Ce has little effect on the morphology of primary α-Al and eutectic Si in the as-cast microstructure, but can induce the formation of new La- or Ce-containing phases, i.e. Al₂LaSi₂ and Al₂CeSi₂. During aging process, an addition of La/Ce significantly delays the precipitation of β″, β′ and β phases, resulting in a postponed occurrence of hardness peak and a slight decrease in hardness. TEM analysis shows that an addition of La/Ce refines the precipitated phases, with more uniform size and distribution. By calculation of the activation energy for precipitate formation, it is found that La/Ce addition increases the thermal stability of the precipitated phases, and Ce brings a more pronounced effect than La. Although traces of La and Ce do not significantly refine the grains in A356.2 alloy, they effectively enhance the stability and refinement degree of the precipitated phases, exhibiting the potential in regulating the strengthening behavior of alloy.

A356.2  /  microalloying  /  lanthanum (La)  /  cerium (Ce)  /  precipitated phase  /  precipitation hardening  /  activation energy  /  precipitation behavior  /  thermodynamics