Study On Work Softening Behavior Of Cu-Cr-Ti-Si Alloy

Cu-Cr-Ti based alloys are widely used in connector,lead frames and other fields due to their high strength,high electrical conductivity and good corrosion resistance.In this thesis,the microstructure and property evolution of peak-aged Cu-Cr-Ti and Cu-Cr-Ti-Si alloys at various aging states during preparation process were studied.The mechanism of work softening behavior of underaged,peak-aged Cu-Cr-Ti-Si alloys and work hardening behavior of over-aged Cu-Cr-Ti-Si alloy,peak-aged Cu-Cr-Ti alloy during the cold rolling are revealed.This work used pure copper?99.95 wt.%?,pure titanium?99.99 wt.%?,Cu-8 wt.%Cr master alloy and pure Si?99.0 wt.%?as raw materials.Cu-Cr-Ti and Cu-Cr-Ti-Si alloy ingots were prepared through?hot rolling-solid solution–aging-cold rolling?.For alloys after aging treatment,it was found that Cr existed in the copper matrix in the form of second phase and Ti and Si existed in the matrix as solute atoms.The addition of trace Si element had the effect of refining grains of alloy at aging state,resulting in finer grains of peak-aged Cu-Cr-Ti-Si alloy than Cu-Cr-Ti alloy.The properties of peak-aged Cu-Cr-Ti alloy and Cu-Cr-Ti-Si alloy after cold rolling were investigated.It was found that the hardness of Cu-Cr-Ti-Si alloy decreased from 192±0.9HV_0.2 to 178±3.8 HV_0.2 when the cold-rolling reduction reached 80%,and work softening occurred.However,the hardness of Cu-Cr-Ti alloy increased with the increase of deformation,showing a significant work hardening phenomenon.The microstructure of the alloys after cold rolling was observed and analyzed by scanning electron microscopy equipped with an electron backscatter diffraction system and transmission electron microscopy.It was found that the proportion of low-angle grain boundaries of the Cu-Cr-Ti-Si alloy with severe plastic deformation decreased,dislocation cells increased,dislocation density slightly decreased that the recovery took placed.Since there were no recrystallized grains,which indicated that recovery led to softening of alloy.No such phenomenon has found for Cu-Cr-Ti alloy.The microstructure and properties of Cu-Cr-Ti-Si alloys at various aging states before and after cold rolling deformation were investigated.The results showed that bcc-Cr phase had been found.In addition,the number of precipitated phases in the peak-aged Cu-Cr-Ti-Si alloy structure was the largest and the spacing was the smallest.The precipitated phase of the over-aged alloy partially dissolved,so the spacing increased,and the grain size also increased.The properties and microstructure of alloys with different aging states after deformation were studied.It was found that the hardness of underaged and peak-aged Cu-0.32Cr-0.059Ti-0.017Si alloys firstly increased,and decreased under greater deformation.The hardness of over-aged Cu-0.32Cr-0.059Ti-0.017Si alloy increased with the increase of deformation.Observing the microstructure of the alloy after cold rolling at different cold-rolling reduction,the reason for softening phenomenon is found to be that underaged and peak-aged Cu-0.32Cr-0.059Ti-0.017Si alloys recovered and the dislocation density decreased.