Continuous And Discontinuous Precipitation Of Cu-Ti-(Al)Alloy

Aging strengthened Cu-Ti alloy is widely used in electronic and electrical engineering because of its excellent mechanical strength and good electrical conductivity,making them an ideal substitute for Cu-Be alloys.In this paper,the phase transformation characteristics of precipitates in Cu-3Ti-（Al）alloys was studied after solid solution and aging treatment.The microstructure of the alloy was observed by metallography microscope and scanning transmission electron microscope,and the conductivity and microhardness were measured.At the same time,the effect of cold deformation treatment and aging treatment process on the properties of the alloy was studied,and the effect of Al addition on the properties and microstructure of Cu-3Ti alloy was also explored.The results were listed as follow:（1）The spinodal decomposition and ordering of Cu-3Ti alloy occurred during the solid solution quenching,resulting in needle-like and metastable states that are consistent with the matrixβ′-Cu₄Ti continuous precipitation phase.However,Cu-3Ti-1Al alloy did not undergo ordering during solution quenching,and obvious spinodal decomposition was observed after aging at 400°C for 1h.With the extension of aging time,needle-like and metastable structures were also observed theβ′-Cu₄Ti ordered phase gradually grows and coarsens,indicating that the addition of Al element delays the process of ordering.The orientation relationship between Cu matrix andβ’-Cu₄Ti is as follows:[001]_Cu//[001]_β’,（310）_Cu//（100）_β’.（2）Discontinuous cellular colonies were precipitated at the grain boundary of Cu-3Ti alloy and Cu-3Ti-1Al alloy during the early stage of aging at 600°C.The microstructure was lamellar structure containingβ-Cu₄Ti andαsolid solution in equilibrium state,and the orientation relationship between them was（111）_α∥（010）_β,[1 10]_α∥[001]_β.The decomposition sequence of Cu-3Ti-（Al）alloys was composition modulation caused by spinodal decomposition of supersaturated solid solution（α₀）→needle-like and metastableβ’-Cu₄Ti continuous precipitation with tetragonal structure→lamellar structure composed of layered equilibriumβ-Cu₄Ti+equilibriumαphase with orthogonal structure.（3）The hardness and electrical conductivity of Cu-3Ti and Cu-3Ti-1Al alloys during low temperature aging were compared.It was found that the addition of Al element increases the hardness of alloy,and the arrival time of the peak hardness of the alloy was advanced from 180 min to 30 min of Cu-3Ti-1Al alloy at 500°C.Compared with Cu-3Ti alloy,the electrical conductivity of Cu-3Ti-1Al alloy was lower than that of Cu-3Ti-1Al alloy under the same aging conditions,indicating that the addition of Al can reduce the electrical conductivity of the alloy.（4）In this paper,Cu-3Ti alloy and Cu-3Ti-Al alloy after solution and cold deformation treatment,respectively,at 450℃aging 90min and 500℃aging 30min achieved good performance,the hardness and conductivity of the alloy were 302.4HV and 13.43%IACS,323.0HV and 7.97%IACS.（5）The cellular structure in Cu-3Ti and Cu-3Ti-1Al alloys was quantitatively analyzed by Image J.It was found that the cellular structure content of Cu-3Ti-1Al alloy was lower than that of Cu-3Ti alloy under the same aging conditions,indicating that the addition of Al element can retard the growth of cellular structure.