Nucleating role of an effective in situ Mg3P2 on Mg2Si in Mg–Al–Si alloys

Refinement and modification effects of the Al–3.5P master alloy on Mg2Si phases in Mg–4Al–2Si alloys were studied in this work. Mg2Si phases in Mg–4Al–2Si alloys can be modified well at 740 °C with the addition of 1.5% Al–3.5P master alloy. The mean size of primary Mg2Si decreases from about 70 μm to less than 15 μm, and the morphology changes from coarse dendritic or equiaxed to polygonal shape. In addition, the amount of eutectic Mg2Si obviously decreases and the morphology changes from coarse Chinese script to fine fiber shape. XRD and EPMA results show that a reaction between AlP and Mg occurs in the melt forming a new Mg3P2 phase which serves as the heterogeneous nucleation substrates of Mg2Si.

Research highlightsIn this paper, the refinement and modification performance of the Al–3.5P master alloy on Mg2Si phases in Mg–4Al–2Si alloys were studied in this work. Significantly, it explored the modification mechanism of P-containing modifier on Mg2Si which may help to enrich the refinement technology of Mg–Si alloys and promote application range of this modifier in industry production process.