Effect of Si addition on microstructure and properties of Cu-Ni-Al alloy
Cu-Ni-Al alloy,as an elastic copper alloy with ultra-high strength and good conductivity,is widely used in electronic industry,aerospace,instrumentation and other fields.Microstructure of Cu-6Ni-2.76Al and Cu-6Ni-2.76Al-0.4Si alloys after aging was studied by means of optical microscope(OM),scanning electron microscopy(SEM),X-ray diffraction(XRD)and scanning transmission electron microscopy(STEM).The results show that the comprehensive properties of the Cu-6Ni-2.76Al alloy after homogenizing annealing at 900 ℃ for 12 h+hot-rolling deformation of 80％+solution treatment at 950 ℃ for 2 h+cold-rolling deformation of 50％and then aging at 500℃ for 8 h are good,the hardness and electrical conductivity are 279.5 HV0.3 and 16.14％IACS,respectively.The strengthening phase of the alloy is nanoscale spherical γ'-Ni3Al particles.The comprehensive properties of the Cu-6Ni-2.76Al-0.4Si alloy after homogenizing annealing at 900 ℃ for 12 h+hot-rolling deformation of 80％+solution treatment at 950 ℃ for 2 h+cold-rolling deformation of 50％and then aging at 450℃for 2 h are excellent,the hardness and electrical conductivity are 313.2 HV0.3 and 13.24％IACS,respectively.The strengthening phases of the alloy are nanoscale spherical particles γ'-Ni3Al phase and 8-Ni2Si phase.The addition of Si element has little effect on the conductivity of the alloy,but it significantly increases its peak hardness and shortens the aging time required to reach the peak hardness,but also reduces the over-aging resistance of the alloy.The orientation relationships among γ'-Ni3Al,δ-Ni2Si precipitate phases and copper matrix are:[001]Cu//[001]Ni3Al//[001]δ;(1(1)0)Cu//(1(1)0)Ni3Al//(100)δ;(110)Cu//(110)Ni3Al∥(010)δ,respectively.The precipitation strengthening effect has the most significant effect on the enhancement of the alloy properties.
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