Research On Microstructure Evolution And Process Window Of Bimetal Tube Via Three-roll Planetary Milling Process

Compared to mono-metal tube,Cu/Al bimetallic tube has many aspects of the advantages.Bimetallic tube not only retain the excellent corrosion resistant of Al alloy,high conductivity and strength of copper,but also can reduce the use of precious metal and drop the costs.Recently,the Three-roll planetary rolling technology was applied into the manufacture of Cu/Al bimetallic tube successfully.Meanwhile,due to the unique processing method,Three-roll planetary rolling shows many advantages in terms of producing bimetallic tube:it can complete the process for one pass,high deformation,high production efficiency,low energy consumption,low costs.Hence,it is necessary to conduct thorough research to the processing of bimetallic tube via three-roll planetary rolling and optimize the processing parameters.First of all,taking the T2Cu/3003Al bimetallic tube as the research object,the microstructure evolution of T2Cu/3003Al under deformation region of three-roll planetary milling were studied.The microstructure state of T2Cu and 3003A1 under different deformation were studied by electron back-scattered diffraction.The stored energy of T2Cu and 3003A1 under different deformation was studied by differential scanning calorimetry,activation energy of 3003A1 under 30%,50%,70%deformation and T2Cu under 3%,12%,25%,37%deformation was calculated based on DSC measurements at heating rates of 10,20 and 30K/min.The results show that,with the increase of deformation,the grain size of T2Cu/3003Al refined obviously and the percentage of twin in pure Cu decreased which transform into low-angle grain boundary.The grain size of Al under 70%deformation was 3-4?m and pure Cu under 37%deformation was 2-3 ?m.With the increase of deformation,the stored energy of T2Cu/3003Al are rising while the activation energy are declining.The stored energy of 3003Al under 70%deformation was 10.89J/g,T2Cu under 25%deformation was 5.90J/g.The activation energy of 3003A1 under 30%deformation was 95.35kJ/mol,T2Cu under 3%deformation was 3.94kJ/mol.In order to optimizing the processing parameters of bimetallic tube,the hot deformation behavior of 3003A1 and T2Cu were studied through the off-line physical simulation on Gleeble-3500 thermo-simulation machine.The deformation parameters of 3003A1 alloy including deformation temperature 293-773K,strain rate 0.01,0.1,1,10s-1,The deformation parameters of T2Cu including deformation temperature 293-1073K,strain rate 0.01.0.1,1,10s-1.The constitutive equation of 3003A1 and T2Cu were established through the Arrhenius constitutive model and Zener-Hollomon parameter.As we all know,strain has heavy effects on the flow stress during deformation process especially under low temperature.So the constitutive equations of 3003A1 and T2Cu in this paper were modified by considering the effects of strain and built more accurate constitutive equations.What's more,the results show that the constitutive equation of T2Cu should be built as the form of piecewise function of temperature,the first temperature section is 293-723K,the second temperature section is 723-1073K.In this paper,the processing maps of 3003A1 and T2Cu were established according to dynamic material model(DMM)at the strains of 0.2,0.4,0.6,0.8 and optimal processing parameters of 3003A1 and T2Cu were accordingly determined.In order to research the effects of processing parameters on microstructure evolution during deformation processing,the microstructure of compressed samples under different deformation parameters were studied through electron back-scattered diffraction(EBSD).The results show that the deformation parameters have significant effects on the microstructure evolution of 3003A1 and T2Cu.The average grain size decreases with the increase of strain rate and the decrease of deformation temperature.However,when the deformation temperature dropped to a certain degree,dynamic recrystallization(DRX)would not take place and large number of low angle grain boundaries occurred inside the metal.Finally,according to the different deformation of 3003A1 and T2Cu in chapter three,processing maps of corresponding strain were built based on DMM,then superimposed the processing maps each other,avoided the instability areas and found out the areas of high power dissipation efficiency of 3003A1 and T2Cu.Then,the optimum processing parameters of bimetallic tube can be obtained.