Research On Solidification Microstructural And Thermal Deformation Simulation Of Alloy2618-ti And Relevant Phase Equilibrium Of This System

Alloy2618is an Al–Cu–Mg alloy with Fe and Ni additions to form intermetallicphase Al9FeNi. This alloy is a heat-treatable alloy developed for aircraft and spaceapplications and auto industry, mainly due to a combination of their high strength toweight ratio and favorable heat resistance. A lot of research work has been done toimprove the mechanical properties of alloy2618over the years, such asmicro-alloying and thermomechanical treatment for this alloy. The beneficial effect ofmicroscale titanium on mechanical properties is resulted from the existence of Al3Tiparticles in the alloy, which can refine the grain structure and inhibit the dynamicrecrystallization of the alloy.In order to exclude the effect of Al9FeNi phase, the Al-Cu-Mg alloys without Feand Ni which contained the same Al and Cu concentation with2618alloy wereinvestigated. Moreover, the Al-Cu-Mg-Ti alloy with high Ti content was prepared bysolid-liquid mixing and near liquidus casting. Then the microstructural evolution ofAl-Cu-Mg-Ti alloy has been investigated using scanning electron microscopy. Theresults show that the grain size of the Al-Cu-Mg-Ti alloy decreases obviously andAl3Ti particles distribute evenly in the as-cast alloy. The size of Al3Ti particles inAl-Cu-Mg-Ti alloy is in the range of2~10μm, which is almost the same as that inAl-7%Ti powders. The morphology of the TiAl3particles changes from fine needle inAl-7%Ti powders to short-rod or lump in Al-Cu-Mg-Ti alloy. When the content of Tiis above1.5%(the adding amount of Al-7%Ti powders exceeds21.4%), the grainrefining effect of Al-7%Ti powders on Al-Cu-Mg-Ti alloy decreases. Besides, theamount of coarse needle-like Al3Ti particles increases obviously. And the pretreatmentfor Al-7%Ti powders is in favor of the uniform distribution of TiAl3particles inAl-Cu-Mg-Ti alloy. After the Al-Cu-Mg-1.5Ti alloys have been re-melted at720℃for different time, the circularity factor of TiAl3particles maintains at0.76. With theincreasing of re-melting time, the average size of TiAl3particles increases rapidlywhen the time is less than20min, then it increases slowly with the time.In order to investigate the influence of strain, strain rate and deformationtemperature on hot compressive deformation of alloy2618-Ti, a comprehensivemodel describing the relationship of the flow stress, strain rate and temperature of thisalloy. The flow stress constitutive equation can be established by the data of the true stress-true strain curve, and the material constants also can be calculated by that. Theresults show that the peak flow stresses of alloy2618-Ti calculated using the proposedconstitutive equations agree well with experimental results. The activation energy ofhot deformation for alloy2618-Ti was306.8kJ/mol, while it was only181kJ/mol foralloy2618. It proves that the existence of much dispersed Al3Ti particles in alloy2618-Ti can suppress the high temperature deformation behavior of this alloy.For further analyze the phase composition of alloy2618-Ti, equilibrating alloymethod was used for determining the phase equilibrium of Al-Cu-Ti ternary system at600℃. The results show that the determinate three-phase region include: Al-η1-Al3Ti,ε2-Al3Ti-τ1, γ1-τ1-τ2, γ1-τ2-τ3, γ1-β-τ3, Al3Ti-Al2Ti-τ1, Al2Ti-AlTi-τ1, AlTi-τ1-τ2,AlTi3-AlTi-τ2, Cu-TiCu4-τ3, TiCu4-Ti2Cu3-τ3, TiCu-Ti2Cu-τ3, β-Cu-τ3, and predict anew ternary phase τ4in this phase equilibrium will appear, and the predictedthree-phase region include AlTi3-τ2-τ4, Ti2Cu-τ3-τ4, α(Ti)-AlTi3-τ4, τ2-τ3-τ4, η1-Al3Ti-ε2,ε2-δ-τ1, δ-γ1-τ1, Ti2Cu3-TiCu-τ3, Ti2Cu3-TiCu-Ti3Cu4, Ti2Cu-α(Ti)-τ4. And the τ4was the predicted new phase.