Comprehensive Control Of Microstructure And Properties Of Cu-Ti Alloy Prepared By Aluminothermic Method

As a typical age hardening alloy comparable to Cu-Be alloy,Cu-Ti alloys are widely used in aerospace,electronic instruments,communications and other departments.Moreover,it can be used as a high-strength and high-conductivity material in conductive springs,interconnector connectors,and other elastic components.For Cu-Ti alloys,most of the research focuses on the structure and properties of alloys with Ti content less than 5 wt.%.In this work,in order to study the evolution of the structure and properties of Cu-Ti alloys in a wider range of composition,Cu-Ti alloys with Ti content of 1 wt.%,2 wt.%,4.5 wt.%,7 wt.%,10 wt.%and 12.5 wt.%were prepared by a novel aluminotherm method which mainly uses the aluminotherm reaction to release a lot of heat to synthesize metal alloys and has many advantages,such as environmental protection,energy saving,simple process,low cost,and unlimited amount of alloying element addition.Then the microstructure and physical mechanism of the as-cast Cu-Ti alloys were analyzed in detail,followed by rolling and solution aging treatment to adjust the overall performance,aiming to obtain alloys with good strength and plasticity,and a certain conductivity to achieve the application of Cu-Ti alloy as an elastic conductive element.The main research results of the experiment are as follows:?1?The microstructure of the as-cast Cu-Ti alloys are a pentagonal equiaxed crystal with a size of 20⁶0?m.With the increase of Ti content,the grain size gradually decreases,the strength and hardness increase while the conductivity and extension decline.When the Ti content is 1 wt.%,it completely dissolves in the copper matrix,and with the increase of the Ti content,the dot-like phase gradually precipitates.When the Ti content is 4.5 wt.%,the precipitated phase grows into a spherical shape.When it exceeds 4.5 wt.%,the Cu₃Ti and Cu₄Ti precipitate phases grow and aggregate,then connect in a network and enrich at the grain boundaries.?2?During the rolling process of as-cast Cu-Ti alloys,occurrence of plastic deformation in the alloys induces plenty of dislocation pile-up and stress concentration,forming lots of deformation texture,refining the grains,which resulting in that the mechanical property shows a remarkable improvement but plasticity significant decreased.Meanwhile,the precipitated phases are broken and partially dissolved,however the type of phases is no obvious change.In addition,due to the reduction of pores and vacancy concentration,the internal density of Cu-Ti alloys are improved significantly,and meanwhile the conductivity tend to increase,which the reason is that the scattering effect of point defects on electrons becomes weaken.?3?The microstructure of aged Cu-Ti alloys is substantially varied as well as the disappearance of work hardening,showing equiaxed dendrites with different sizes.The grain size of aged alloys shows a significant decrease compared with that of as-cast alloys,the value is approximately 30?m.Moreover,the“throughout type”twinning structure can be observed within the grains,meliorating the plasticity of aged alloys notably,which exhibits5⁷ fold to that of as-rolled alloys,reaching 40%.For Cu-10wt.%alloy,the Cu₃Ti phase vanished after heat treatment.To sum up,the optimum heat treatment process of Cu-Ti alloys is solid solution treatment at 860? for 1 h,cooling and then aging at 450? for 2h.Through cool deformation and heat treatment,the properties exist a significantly improvement compared with that of as-cast alloys,exhibiting outstanding hardness and strength as well as good plasticity under the premise that the conductivity still maintains in a high level.