The Evolution Of Mechanical Behavior And The Microstructure Of Cu-Al-Ni Alloy During Thermomechanical Treatment

Copper and copper alloys are widely used in lead frame materials,railway contact wires,electrical connectors,heat transfer components and other electronic and electrical industries.It is of great significance to study the preparation process of high-performance copper alloy materials for China’s national economy and national defense and military construction.As a low stacking fault energy precipitation strengthened copper alloy,the research on the evolution of microstructure and mechanical properties during deformation and aging is very representative and instructive for the development of this kind of copper alloy.In this paper,Cu-5.0wt%Al-3.0wt%Ni and Cu-7.5wt%Al-3.0wt%Ni alloys were designed and prepared by alloying method.By studying the recrystallization behavior of Cu-Al-Ni alloy,the mechanical properties and microstructure evolution during SHPB deformation and aging as well as secondary deformation and aging,the strength and plasticity matching of the alloy samples were successfully improved.Meanwhile,the formation and disappearance mechanism of twins during deformation were simulated by PFC method.And the electrochemical corrosion properties were studied.The conclusions are as follows:（1）After unidirectional rolling at room temperature with 70%deformation,the best recrystallization annealing process is annealing at 700℃for 2h.After SHPB deformation,a large number of cellular substructures and deformation twins are formed in the recrystallized alloy,which greatly improves the strength of the alloy.After aging at 350℃for 1h,a large number of undistorted recrystallized grains and annealing twins are formed in the microstructure,and a large number of nano second phase particles are precipitated.The strength and hardness of the alloy increase at first and then decrease with the increase of aging temperature,However,the ductility continues to improve.The maximum strength of797.06MPa,good elongation of 19.25%and conductivity of 13.86%IACS were obtained at350℃for 1h.（2）During the aging process,the precipitated nano particles hinder the dislocation recovery and recrystallization,and improve the thermal stability of the alloy.The deformed alloy begins to soften after holding at 350℃for 1 hour,resulting in the decrease of strength and hardness.The reason is that the addition of Ni element introduces the precipitated Ni Al and Ni₃Al particles into the alloy.（3）The formation and disappearance mechanism of twin boundary was qualitatively elucidated by PFC method.The formation of grain boundary is caused by the superposition of a large number of dislocation pairs.The original grain boundary is broken by external stress,forming a small angle subcrystalline structure.Through the interaction between grain boundaries and dislocations,including dislocation climbing and sliding,dislocation decomposition,increment and annihilation,dislocation redistribution at grain boundaries,large angle grain boundaries are formed in the process of subcrystalline migration,and finally complete grains are formed.（4）The Cu-Al-Ni alloy was corroded in 3.5%Na Cl solution to form a double-layer structure corrosion product,which is composed of white flocculent Cu₂（OH）₃Cl in the outer layer and dense black Cu₂O dominated oxide in the inner layer.The dense structure of the inner oxide plays a passivation and protection role for the material.（5）After multistage deformation and annealing,the plasticity of Cu-Al-Ni alloy is improved on the premise of maintaining high strength.The improvement can be attributed to the adjustment of deformation strengthening and precipitation strengthening by multistage aging deformation.Finally,the best strength and plasticity matching of Cu-7.5Al-3Ni alloy samples were obtained when the comprehensive process was 80%unidirectional cold rolling followed by holding at 350℃for 60min,and then 50%cold rolling followed by aging at 350℃for 15min.The strength and elongation of Cu-7.5Al-3Ni alloy samples were 774.35mpa and 5.29%,respectively.