To reveal the influence and mechanism of Bi elements with different amount in eutectic phase on the undercooled eutectic solidification structure,Al-Cu-Si-xBi(x=0％、0.01％、0.03％、0.05％、0.07％)eutectic alloys were prepared via using a gravity solidified method.The effect of Bi on the solidification structure of Al-Cu-Si ternery eutectic alloy was investigated.The results show that the Al-Cu-Si ternary eutectic alloy has α-Al/θ-Al2Cu binary eutectic and α-Al/θ-Al2 Cu/β-Si ternary eutectic.The structure is called a bimodal eutectic structure.When Bi is not added,the α-Al/θ-Al2Cu binary eutectic exhibits a typical radial chrysanthemum cluster morphology,the Si phase in α-Al/θ-Al2 Cu/β-Si ternary eutectic exhibits elongated needle like morphology.The bimodal eutectic structure is relatively inhomogeneous.With the addition of Bi,α-Al/θ-Al2Cu binary eutectic exhibits a uniform and fine short layer structure,and the Si phase in α-Al/θ-Al2Cu/β-Si ternary eutectic exhibits dot needle-like morphology.The difference in interlayer spacing of the bimodal eutectic structure gradually decreases.When the amount of Bi added is 0.05％,the modification effect is the optimal,and the bimodal eutectic structure is the most uniform and fine.alloy hardness is optimal.
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