Effect of Ce-rich Rare Earth on Solidification Microstructure of Multicomponent Al-Si Piston Alloy

The effect of Ce-rich rare earth (0.1wt%, 0.3wt%, 0.5wt%) on the solidification microstructure of multivariate near-eutectic Al-11.5Si-4Cu-2Ni-1Mg-0.5Fe (wt%) piston alloy was studied by DSC, optical microscopy and scanning electron microscopy. It is found that the addition of Ce-rich rare earth has obvious effects on the solidification temperature, morphology and volume fraction of eutectic silicon and various second phases of the alloy.The addition of Ce-rich rare earth reduces the Al-Si eutectic temperature and increases the precipitation temperature of T-Al₉FeNi phase and δ-Al₃CuNi phase.When the addition of Ce-rich rare earth is 0.3wt%, the modification effect of eutectic silicon is best, T-Al₉FeNi phase changes from the initial lath shape to the small block shape, the volume fraction decreases to 3.22vol%, and the δ-Al₃CuNi phase changes from the initial flake shape to fishbone shape, the volume fraction increases to 6.47vol%. La and Ce atoms in the Ce-rich rare earth are enriched at the front of the solid-liquid interface during the solidification process, which increases the compositional supercooling and refines the eutectic structure. When the content of Ce-rich rare earth is 0.5wt%, long needle-like rare earth-rich phase appears in the alloy.