Mechanism of the Correlation between the Electrical Conductivity of the Cu-Ni-Si-xLa Hot-rolled Sheets and their Characteristic Microstructures
To investigate the effects of La addition on the microstructure and properties of C70250 alloys,the microstructure,grain size and distribution,and evolution of precipitates in Cu-Ni-Si-xLa alloys in the cast,homogenized,and hot-rolled states were investigated via optical microscope,scanning electron microscope,electron backscatter diffraction,microhardness testing,electrical conductivity testing,and tensile testing.The influence of different La contents on the alloy performance before processing was analysed.The results show that the addition of La in the outer region of the cast ingot results in the formation of a fine-grained region,and the grain size of this region first refines and then coarsens with increasing La content.The dendritic structure is obvious in the Base alloy and alloy with 0.05 wt.%La added,and the grain boundaries are blurred.After a suitable amount of La is added to the cast ingot,a fine-grain strengthening effect is produced,and the hardness increases.In the Base alloy,the recrystallized grains are distributed on both sides in the width direction of the fibrous grains.However,in the alloy with La added,the recrystallized grains are mostly distributed at the ends of the fibrous grains and tend to grow towards the middle of the grains.The recrystallized grains sever the fibrous grains,thereby leading to a reduction in their length.The addition of an appropriate amount of La improves the hot-rolled strength of the Cu-2.8Ni-0.66Si alloy,and the best comprehensive performance is obtained when the addition of 0.2 wt.%La,with a tensile strength of 441 MPa and an electrical conductivity of 18.2%IACS.
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