Effects of solidification parameters on microstructure and mechanical properties of continuous columnar-grained Cu-Al-Ni alloy

Effects of melt temperature and casting speed on microstructure and mechanical properties of Cu-14%Al-3.8%Ni (mass fraction) alloy wires fabricated by continuous unidirectional solidification technology were investigated. It was found that the average size of columnar grain in the alloy decreased and grain boundary turned clear and straight with increasing the casting speed at a given melt temperature. When the melt temperature was up to 1 280 °C, the β1 phase gradually transformed into lozenged and lanciform γ1' martensite, as well as parallel-sided plate β1' martensite. The alloy with numerous coarsely dendritic γ2 phase has poor mechanical properties due to the difficulty of stress-induced martensitic transformation. When the amount of the γ2 phase reduced and the coarse dendrite γ2 phase evolved into the fine square particles, the elongation of the alloy increased gradually with a decrease in tensile strength. Meanwhile, the plasticity of the alloy could also be improved by increasing the amount and size of martensites, particularly the lanciform γ1' martensite. When the alloy was almost composed of coarse lanciform γ1' martensite, the tensile strength and elongation of the alloy could be up to 772 MPa and 18.9%, respectively, and the tensile curve consisted of three transformation platforms.