Abstract
In this study, in–situ eutectic Mg2Si reinforced AZ61 composites unmodified and modified with Sr addition are fabricated. The effects of Sr addition on the morphology and size of Mg2Si phase, α–Mg matrix grains, its refining mechanism and mechanical properties of Mg2Si/AZ61 composites are investigated. The results show that the morphology of eutectic Mg2Si phases in Mg2Si/AZ61 composites is significantly modified from coarse Chinese character to polygonal shape with Sr addition, and Sr atoms are preferentially absorbed on the {100} surfaces of Mg2Si phase, which suppresses the preferred growth along <100> direction. Besides, some Sr atoms dissolved into the Mg2Si lattice, change the growth mode and improve its morphology. Moreover, Al4Sr formed during solidification act as the heterogeneous nucleation core of Mg2Si, to refine the size of Mg2Si from 11.37 to 2.11 μm. Meanwhile, the average size of α–Mg matrix is also refined to 50.4 μm, decreased by 49.7%, indicating that both eutectic Mg2Si phase and α–Mg grains were significantly refined by Sr addition. Compared with unmodified Mg2Si/AZ61 composite, the strength and ductility of Sr modified Mg2Si/AZ61 composites are improved simultaneously, especially the ductility increased by 63%.
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