Study On Microstructure And Properties Of Cu-Al-Ni Alloy With Ultrafine Grained And Twin Structure

Copper and its alloys are widely used in lead frames of integrated circuits and electrical connectors of new energy vehicles because of their excellent electrical conductivity,thermal conductivity and ductility.The vigorous development of these industries has put forward higher requirements for the strength and ductility of copper alloys,but the strength and ductility are naturally opposed.To prepare high strength and high elongation copper alloys has become a hot spot of researchers for a long time.In recent years,copper alloys with high strength and high elongation have been prepared by introducing twin structure into Cu-Al alloy.In order to introduce twins into traditional precipitation strengthened copper alloys,Cu-7at%Al-3at%Ni and Cu-7at%Al-6at%Ni alloys were designed and prepared by alloying on the basis of Cu-7at%Al binary alloy in this work.The ultra-fine grain and twin structure materials were obtained by multi-directional forging and cold rolling,the microstructure was controlled and the precipitated phase was introduced by proper aging treatment,in order to improve the strength and elongation of Cu-Al-Ni alloy.This paper mainly studies the effect of Ni content on the microstructure and precipitated phase types of Cu-Al-Ni alloy during cold rolling aging treatment and multi-directional forging aging treatment.Taking Cu-7at%Al-3at%Ni alloy as the research object,the microstructure evolution and grain boundary orientation distribution of Cu-7at%Al-3at%Ni alloy during cold rolling treatment and multi-directional forging of are discussed.(1)The composition and microstructure test show that Cu-7at%Al,Cu-7at%Al-3at%Ni and Cu-7at%Al-6at%Ni alloy contain a large number of dislocations and substructures after multi-directional forging aging treatment and cold rolling aging treatment,and the fracture surface contains a large number of dimples,indicating that the materials are ductile fracture and have good ductility.The composition test of Cu-7at%Al-3at%Ni and Cu-7at%Al-6at%Ni alloy shows that the precipitated phase is NiAl phase.Under the process conditions in this paper,the change of Ni content does not change the type of precipitated phase.(2)The TEM characterization of Cu-7at%Al-3at%Ni alloy shows that there are a large number of high density dislocations,substructure and nanometer precipitates in Cu-7at%Al-3at%Ni alloy after cold rolling and multi-directional forging.In addition,deformation twins with lamellar thickness of about 30 nm are also observed,which will have a good effect on the ductility of the alloy.The difference is that it can be observed that the dislocation density in the multi-directional forging treatment is significantly higher than that in the cold rolling treatment,and there is almost no complete grain structure,but the recrystallized grains can be observed in the cold rolling treatment.By calibrating the selected area electron diffraction pattern of the precipitated phase,the precipitated phase of the alloy is B2 NiAl phase.Through the HRTEM image,it can be determined that the mismatch degree of cold rolled NiAl phase at the boundary of the two phases is 0.009,NiAl phase and Cu matrix has a good coherent relationship,while the sample after multi-directional forging treatment shows a semi-coherent relationship between NiAl phase and Cu matrix with a misalignment of 0.11.(3)The EBSD characterization of Cu-7at%Al-3at%Ni alloy shows that there are a large amount of substructure,deformed microstructure and recrystallization structure of Cu-7at%Al-3at%Ni alloy after multi-stage cold rolling aging treatment.After multi-directional forging aging,there is only a small amount of recrystallized structure,and still retains a large number of substructure and deformed structure.After cold rolling aging,the large-angle grain boundary of Cu-7at%Al-3at%Ni alloy accounts for 53.5%,the average grain size is 0.65 ?m,and the grain direction is mainly concentrated in the {101} face.after multi-directional forging aging treatment,the large-angle grain boundary accounts for 60%,and the average grain size is 0.64?m.The orientation distribution function analysis shows that after multi-stage cold rolling aging,Cu-7at%Al-3at%Ni alloy mainly has strong standard Goss/Brass texture({110}<115>),strong A texture({110}<111>),?-linear texture and P texture({011}<211>),and weak Rotated-Goss texture({110}<110>).After multi-directional forging aging,Cu-7at%Al-3at%Ni alloy mainly has strong standard Brass texture({110}<112>)and strong Goss/Brass texture({110}<115>),weak Goss texture({110}<100>)and weak Copper-twin texture({552}<115>).(4)The strengthening mechanism of the samples after cold rolling and multi-directional forging aging treatment is quantitatively analyzed.The results show that the greatest contribution to the strength of Cu-7at%Al-3at%Ni alloy is work hardening and grain boundary strengthening,which is mainly due to the introduction of a large number of dislocations in the deformation process,and dislocations divide grains to form fine grains.However,the solid solution strengthening and precipitation strengthening contribute relatively little to the strength of the alloy,and the deformation mode has little effect on the solid solution strengthening and precipitation strengthening.