Study On Microstructure Evolution And Strengthening Mechanism Of Cu-Ni-Mn Alloy

Cu-Ni-Mn alloy has high strength,high modulus of elasticity,excellent thermal conductivity and corrosion resistance.It is commonly used as elastic components and structural parts,and widely used in electronic appliances,oil drilling,aerospace and other fields.At present,the research on Cu-Ni-Mn system alloy is mainly focused on the strengthening mechanism of dispersed precipitated particles,but less on solution strengthening and deformation strengthening.In this paper,Cu-Ni-Mn alloy is taken as the research object.By means of SEM,TEM and tensile test,the effects of Ni and Mn elements on the solution strengthening of Cu-Ni-Mn alloy,the precipitation behavior and strengthening mechanism of Cu-Ni-Mn alloy during aging,and the effects of thermomechanical treatment process on the mechanical properties of Cu-Ni-Mn alloy are systematically studied.Through systematic research and analysis,the specific conclusions are as follows:(1)The strengthening mechanism of solid solution Cu-Ni-Mn alloy was quantitatively analyzed with the help of strengthening model.The results show that solid solution strengthening is the main strengthening mechanism of solid solution alloy after solution treatment.In the solid solution Cu-Ni-Mn alloy,the yield strength increases with the increase of solute content,and the synergistic addition of Ni and Mn elements will lead to higher atomic size mismatch and hardening constant,which is the main reason for stronger solid solution strengthening effect in Cu-Ni-Mn alloy.Because the atomic size mismatch of Mn solute is higher,the solid solution strengthening effect of Mn Addition is higher than that of Ni.In addition,in the Cu-Ni-Mn alloy with a certain Ni content,with the increase of Mn content,the hardening constant value of Ni will increase significantly,which shows that the addition of Mn can enhance the solid solution strengthening effect of Ni.On the contrary,when the content of Ni changes,the hardening constant of Mn changes little.Therefore,the increase of solid solution strengthening of Cu Ni Mn alloy is mainly attributed to the enhancement of Ni solid solution strengthening,and the addition of Mn is the key factor to enhance Ni solid solution strengthening.(2)In Cu-25Ni-25 Mn alloy,two kinds of continuous / discontinuous desolvention transformation of NiMn are desolvention and precipitation.At 350 ℃ and below,the discontinuous desolvention is the main way of Ni Mn phase precipitation in Cu-25Ni-25 Mn alloy;when the aging temperature rises to 450 ℃,the discontinuous desolvention is inhibited,and the continuous desolvention becomes the main way of NiMn phase desolvention and precipitation.The peak hardness of Cu-25Ni-25 Mn alloy aged at 350 ℃ and 450 ℃ is471HV5 and 500HV5,respectively.The hardness of the alloy can be effectively improved by the two methods of desolvention.The continuous desolvention of NiMn phase particles has a coherent relationship with the matrix.Based on the limited layer slip model,the yield strength of Cu-25Ni-25 Mn alloy after discontinuous desolvation at 350 ℃ can be calculated.Compared with the measured values,it is found that the theoretical derivation is approximately close to the experimental value,indicating that the discontinuous desolvation structure in Cu-25Ni-25 Mn alloy can obtain high strength,which is the result of strong hindrance of nano-scale NiMn phase and Cu matrix relative dislocation.(3)The hardness of cold-rolled Cu-25Ni-25 Mn alloy increases with the increase of shape variable.After 80% cold rolling,the hardness of Cu-25Ni-25 Mn alloy reached 300HV5,which increased 175HV5.(4)After cold rolling and aging treatment,the peak hardness of Cu-25Ni-25 Mn alloy increased obviously.The hardness of 80% cold-rolled Cu-25Ni-25 Mn alloy aged at 350 ℃for 24 hours can reach 550HV5,which is 100HV5 higher than the peak hardness of solid solution alloy.The high hardness of cold-rolled Cu-25Ni-25 Mn alloy during aging is the comprehensive effect of dislocation strengthening and discontinuous desolvation structure strengthening.On the other hand,with the increase of shape variable,the time to reach the peak hardness of Cu-25Ni-25 Mn alloy is shortened under different temperature conditions.The peak aging time of solid solution,40% cold rolled and 80% cold rolled alloy is 40 h,14 h and 2 h respectively at 450 ℃.In addition,the hardness increment of cold-rolled Cu-25Ni-25 Mn alloy is lower than that of solid solution alloy due to the reduction of dislocation strengthening effect caused by the recovery reaction during aging at 350 ℃.