Investigation On Microstructure And Properties Of Cu-Ti-Mg Alloys

The Cu-3Ti-2Mg alloy obtained excellent properties according to the test results of electrical conductivity and hardness of Cu-3Ti-xMg（x=0,1,1.5,2）alloy at as-cast state.The microstructures and properties of Cu-3Ti-2Mg alloy at as-cast state,solid solution and aging state were investigated,and the effect of prior cold deformation on the microstructures and properties of Cu-3Ti-2Mg alloy was studied as well.The microstructures and phase constituents were characterized by optical microscope（OM）,scanning electron microscope（SEM）,X-ray diffractometer（XRD）and transmission electron microscope（TEM）,and the hardness,electrical conductivity and elastic modulus were measured.The following conclusions can be obtained from above investigations.（1）Mg addition improves the electrical conductivity and hardness of as-cast Cu-3Ti alloy.The electrical conductivity and hardness of Cu-3Ti-2Mg alloy are 12.5%IACS and 279HV,respectively.The as-cast Cu-3Ti-2Mg alloy presents typical dentrite microstructure and mainly consists ofα-Cu（Ti,Mg）,Cu₂Mg phase and coarse laminar Cu₄Ti phase.（2）Cu-3Ti-2Mg alloy after solution treatment at 700℃for 4h has the minimum electrical conductivity and microstructure without laminar Cu₄Ti phase.（3）A large number of fine and well distributed precipitates generate in the Cu matrix after appropriate solid solution and aging treatment,the hardness and electrical conductivity of Cu-3Ti-2Mg alloy increase obviously.The strengthening effect of the Cu-3Ti-2Mg alloy can be attributed to the formation of fine precipitated Cu₂Mg phase and continuous,coherent and metastableβ′-Cu₄Ti.With the increase of the aging time and the temperature,the precipitates become coarse and discontinuous,incoherent and stable precipitateβ-Cu₃Ti phase start to grow,the stableβ-Cu₄Ti phase increases with consumingβ′-Cu₄Ti phase,and thus,the hardness decreases.Due to the formation of Cu₂Mg,β′-Cu₄Ti,β-Cu₃Ti andβ-Cu₄Ti,Ti concentrations are reduced efficiently in the Cu matrix.And thus,increases the electrical conductivity of Cu-3Ti-2Mg alloy.In the range of experiments,the optimal electrical conductivity and hardness for Cu-3Ti-2Mg alloy can be obtained after solid solution at 700℃for 4h and aging at 450℃for 4h,which are 15.3%IACS and 344HV,respectively.（4）The prior cold deformation before aging enhances the distortion energy of Cu-3Ti-2Mg alloy and promotes the precipitation of secondary phases.Consequently,the electrical conductivity and hardness of Cu-3Ti-2Mg alloy are increased remarkedly and the aging time reached the peak hardness is shortened.The electrical conductivity and hardness of Cu-3Ti-2Mg alloy are 16.7%IACS and 328HV after 60%cold deformation and aging at 450℃for 2h.