电阻率与强度性能的关联及铜合金性能分区

铜合金以低电阻率为特征,由于电阻率与强度存在着共同的微观结构机理,两者往往协同变化,而导致难以对合金进行性能的全面评估和选材.本文以Cu-Ni-Mo合金作为研究对象,以团簇结构Mo_1-Ni_(12)]构建固溶体的近程序结构模型,解析了电阻率和强度依赖于成分的定量变化规律,并定义了拉伸强度/电阻率的值为代表合金本质特性的"强阻比",得到了完全固溶态Cu-Ni-Mo合金的强阻比为7×10~8MPa/?·m,完全析出态的强阻比为(310—490)×10~8MPa/?·m.进而应用强阻比对常用铜合金进行了性能分区,给出铜合金材料选材的依据,得出了基于Cu-(Cr, Zr, Mg, Ag, Cd)等二元基础体系的铜合金适用于高强高导应用,而基于Cu-(Be, Ni, Sn, Fe, Zn, Ti, Al)等为基础二元体系的铜合金不能实现高强高导.该强阻比为310的特征性能分界线的发现为合金性能的全面评估提供了量化依据,可指导高强高导铜合金的选材和研发.

Correlation between electrical resistivity and strength of copper alloy and material classification

Low electrical resistivity and high strength are a basic requirements for copper alloys.However,it has been widely known that these two properties are contradictory to each other:high electrical resistivity means extensive electron scattering by obstacles in the alloy,which in turn blocks dislocation movement to enhance mechanical strength.That is to say,any increase in strength necessarily brings about an increase in electrical resistivity.Essentially,strength and electrical resistivity are coupled in metal alloy as both are issued from a similar microstructural mechanism. That is why it is generally difficult to evaluate these alloys comprehensively and to select the materials appropriately. #br#The present work addresses this fundamental problem by analyzing the dependence of hardness (in relation to strength) and electrical resistivity on solute content for deliberately designed ternaryMo_{y/(y+ 12)}Ni_12/(y+12)]_xCu_100-x alloys (at.%),where x=0.3-15.0 is the total solute content,y=0.5-6.0 is the ratio between Mo and Ni.The Mo-centered and Ni-nearest-neighboredMo₁-Ni₁₂]cluster structure are used to construct a short-range-order structure model of solid solution.The clusterMo₁-Ni₁₂]in solution enhances the strength,without increasing the electrical resistivity much,for the solutes are organized into cluster-type local atomic aggregates that reduce the dislocation mobility more strongly than electron scattering.The short-range-order structure has an essentially identical function for strength and electrical resistivity. In this solution state,both hardness and resistivity increase linearly with solute content increasing.When the solute constituents do not meet the requirement for ideal solution,i.e.,Mo-Ni ratio exceeds 1/12,the maximum value that the clusterMo₁-Ni₁₂]can accommodate,the solid solution should be destabilized and precipitation should occur,such as Mo precipitation in this case.The deviation from the linear change of resistivity and strength with solute content are caused by different alloy states,that is,solid solution and precipitation,which contribute to the resistivity and strength differently.Here we define a new term,the ratio of residual tensile strength to residual electrical resistivity,i.e.the “strength/resistivity ratio” in short,which represents an essential property of the alloy system.This ratio is 7×10⁸ MPa/Ω· m) for the Cu-Ni-Mo alloy in complete solid solution state,and it is in a range of (310-490) 10⁸ MPa/Ω·m) for the Cu-Ni-Mo alloys in a fully precipitation state (i.e.,most of Mo solute atoms precipitate out of the Cu matrix). #br#Finally this new parameter is applied to the classification of common copper industrial alloys for the purpose of laying the basis for material selection.It is found that the strength/resistivity ratio of 310 effectively marks the boundary between the fully precipitated state and precipitation plus solution state.Using this criterion,it is concluded that alloys based on Cu-(Cr,Zr,Mg,Ag,Cd) are suitable for high-strength and high-conductivity applications.However,alloys based on binary systems Cu-(Be,Ni,Sn,Fe,Zn,Ti,Al) cannot realize the same purpose.The finding of the line dividing the characteristic properties of alloy having a strength-resistivity-ratio of 310 provides a key quantitative basis for comprehensively evaluating the alloy performance,which can effectively guide material selection and development of high strength and high conductivity copper alloys.