| The CuNiSi series alloy with high strength and high conductivity are widely used in the manufacture of connectors,lead frames and high-speed contact wires due to their excellent strength and electrical conductivity combination.Adding a small amount of Co to the CuNiSi can further improve the properties,but the increase of alloying element content makes it more difficult for solid solution of the CuNiCoSi alloy,while insufficient solid solution can not play the role of alloy elements..Therefore,it is necessary to reveal the evolution mechanisms of grain structure,precipitates and properties of CuNiCoSi alloy during the solid solution process,and determine the influences of solution temperature,time and deformation.That is prominent for optimization of the manufacturing process,play the full role of the alloying elements and further improve the properties of the CuNiCoSi alloys.In this paper,the grain structure and precipitates of the CuNiCoSi alloy in different rolling states were characterized.On this basis,the effects of solution temperature and time on the microstructure and properties of the cold rolled CuNiCoSi alloy strip were studied.Besides,the effects of cold rolling before solution and after aging on the CuNiCoSi alloy were studied.Firstly,the microstructure evolution of the CuNiCoSi during the rolling process was analyzed,and then the grain structure and precipitate structure of the cold rolled CuNiCoSi were characterized after solid solution treated at different temperatures.The results show that the grain structure of the CuNiCoSi alloy is refined with the increase of the total rolling deformation,but the size of the(Ni,Co)x Si precipitates increases to a certain extent due to the thermal effect of annealing.The solution rate and final solution degree of the cold rolled CuNiCoSi sheet are mainly determined by solution temperature rather than time.The relationship between solubility and temperature is nonlinear,and there might be a temperature range for rapid decomposition of the precipitates.In order to accurately determine the effect of solid solution time,the cold rolled CuNiCoSi sheet was solid solution treated at 1000 oC for 15-120 s,and then some samples were aged at 500 oC for 2 h.The grain structure,precipitate morphology,mechanical properties and electrical conductivity of the samples were analyzed.The results show that the high temperature recovery,recrystallization and precipitate decomposition of the cold rolled CuNiCoSi alloy occur mainly between 15 and 30 s at the solution temperature of 1000 oC,and the alloy grains coarsen with prolonged solution time,but the residual precipitates remain unchanged.By precisely controlling the solution time,full solution can be achieved without excessive grain coarsening.Over long solution time has adverse effects on the strength and elongation of the alloy.To further improve the properties of the CuNiCoSi,the effect of cold rolling before solution and after aging on its microstructure and properties were studied.It is found that the larger the cold rolling deformation before solution,the higher the hardening degree,and the finer the grain structure after solution.After aging,a cold rolling can further improve the strength,but decrease the elongation and conductivity.In general,the effect of cold rolling before solution and after aging on mechanical properties of the alloy fit with the general material science mechanism,but the rolling deformation before solid solution has a certain effect on the aging precipitation behavior and needs further study. |
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