Effects of trace ytterbium addition on microstructure,mechanical and thermal properties of hypoeutectic Al-5Ni alloy

Over the past decade,the cast aluminum alloys with excellent mechanical and conductivity properties have emerged as potential materials for thermal management.However,the traditional Al-Si based alloys are difficult to make significant breakthrough in conductivity performance.The hypoeutectic Al-5Ni alloy also possesses sound castability and is expected to be applied in thermal management applications.In this study,the effects of ytterbium(Yb element) at 0-0.5 wt% on the microstructures as well as the electrical/thermal conductivity and mechanical properties of the Al-5Ni alloy were systematically investigated.The experimental results indicate that the addition of Yb at a relatively low amount not only reduces the secondary dendrite arm spacing of the α-Al grains,but also modifies the morphology and distribution of eutectic boundary phase.Moreover,it is found that the dosage of Yb at 0.3 wt% in the Al-5Ni alloy can simultaneously improve the yield strength,ultimate tensile strength and electrical/thermal conductivity.The strengthening and toughening of the Al-5Ni alloy are mainly attributed to the decrease of secondary dendrite arm spacing and the improvement of eutectic phases.The transmission electron microscopy/selected area electron diffraction(TEM/SAED) analysis indicates that the ytterbium in Al-5Ni alloy will form Al_(3)Yb phase,which mainly agglomerates in the Al_(3)Ni phase region.This phase is helpful to decrease the solubility of impurity elements(e.g.,Fe and Si) in the α-Al matrix,which is beneficial to electrical/thermal conductivity.The value of this study lays foundation for manufacturing Al-Ni alloys with high thermal conductivity and acceptable mechanical properties.