LAUSR

In this work, the effect of the addition of Bi combined with T6 treatment on microstructure and tensile properties of Sr‐modified Al–15Mg2Si–3Cu composite is investigated. The results show that the refinement effect of Sr on primary Mg2Si is further enhanced via the combined addition of Bi. Interestingly, the truncated octahedral primary Mg2Si with the smallest size (11.5 μm) is obtained by adding 0.1% Sr and 1% Bi, which is distinctly different from the cubic shape modified by single 0.1% Sr. Consequently, as a precursor with strong diffusion of Mg and Si atoms during T6 treatment, the truncated octahedral primary Mg2Si is completely transformed into spherical morphology with the highest sphericity (0.92) solution treated at 500 °C for 6 h. Additionally, further results reveal that the co‐modification of Sr + Bi is more efficient not only in promoting the spheroidization of primary Mg2Si, but also obtaining the fine dot‐like eutectic Mg2Si than single modification of Sr or Bi. As a result, the tensile strength and elongation are significantly enhanced to 374 MPa and 4.75%, respectively. Thereby, this work offers an alternative co‐modification system combined with T6 treatment to synthesize the spherical primary Mg2Si, which is helpful to prepare the high performance Al–Mg2Si composite.