Abstract: In order to improve the coupling effect of grain refinement and metamorphic refinement of A356 aluminum alloy. The mechanism of the composite treatment of adding AlTiB and Ce on the organization regulation law of α-Al grains and eutectic Si phase and the enhancement of mechanical properties were systematically investigated by using XRD, OM and TEM and mechanical property tests after heat treatment. The results showed that the coupling mechanism of AlTiB and Ce can significantly refine the α-Al grains and improve the morphology of eutectic Si. With the addition of 0.9% AlTiB and 0.3% Ce, α-Al secondary dendrite spacing refine from 23.71 μm to 17.44 μm, the average length of eutectic Si is shortened from 22.3 μm to 7.4 μm, and its morphology is transformed from a coarse needle-like shape to a rounded rod. The in-situ precipitated Ti₂Al₂₀Ce exists in the matrix in a diffusely distributed morphology, and combines well with the interface of the Si rich phase to form highly efficient heterogeneous nucleation sites; The tensile strength, elongation and Brinell hardness of the alloy in this composition reach288.5 MPa, 189 MPa, 4.9% and 59.5 HB, respectively, which are 61.5%, 23.8%, 53.1% and 29.4%higher compared with the pristine state of the aluminum alloy, respectively.

Key words: A356 aluminum alloy, grain refinement, composite modification, mechanical properties, eutectic Si modification