In situ nanocrystals manipulate solidification behavior and microstructures of hypereutectic Al-Si alloys by Zr-based amorphous alloys

Abstract

In this study, different contents (0.0, 0.1, 0.2, and 0.4 wt.%) of Zr55Cu30Al10Ni5 amorphous alloys (Zr-AA) are used to manipulate hypereutectic Al-Si alloys. The edge-to-edge model shows that there is a perfect lattice matching between the crystallized phases and α-Al and Si phases. The thermal analysis of solidification behavior of hypereutectic Al-Si alloys unmanipulated and manipulated by Zr-AA, indicates that the addition of Zr-AA greatly promotes the nucleation of primary Si and significantly accelerates the process of eutectic reaction. When manipulated by the optimal content of 0.2 wt.% Zr-AA, the sizes of α-Al dendrites and primary Si decrease from 212.46 μm and 19.24 μm to 143.39 μm and 16.47 μm, respectively. The eutectic Si changes from needle-like to rod-like and exhibits a mean size decrease from 20.21 μm to 11.69 μm. Meanwhile, alloys exhibit ultimate tensile strength of 362 MPa and fraction strain of 2.21% after 0.2 wt.% Zr-AA manipulation, which are 23% and 37% higher than those of the unmanipulated alloy (295 MPa and 1.61%). The strengthening mechanisms of hypereutectic Al-Si alloys manipulated by in situ nanocrystals crystallized in the melt are mainly attributed to the fine grain strengthening effect and precipitation strengthening effect. The increase in plasticity is due to the refinement and morphology improvement of Si phases.