Study On The Phase Relationship Of Al-Ti-B-Er System And The Refinement Effect Of Intermediate Alloy On 6111 Aluminum Alloy

With the rapid development of modern industry,traditional aluminum alloys are gradually unable to meet higher performance requirements.Grain refinement has become an indispensable process in modern aluminum processing industry.The most widely used grain refiner is Al-Ti-B.However,Al-Ti-B has a refinement of“poisoning”in aluminum alloy containing Cr,Zr and Si elements,and Ti B₂ particles are easy to gather,making the development of new grain fine agents very agent.In recent years,Al-Ti-B-Er refiners have received widespread attention because the addition of rare earth elements can comprehensively improve refining performance.Therefore,this work investigates the phase relationship of the Al rich region in the Al-Ti-B-Er system to understand the phase change behavior and organizational evolution of intermediate alloys.On the basis of phase relationship,the impact of intermediate alloys on micro-organization and performance on 6111 aluminum alloy.The main work and research results of this topic are as follows:The phase equilibria of the Al-Er binary system have been investigated through both experiments and CALPHAD method.The phase relationship in the compositional range of 0-50 at.%Er was experimentally redetermined using scanning electron microscopy（SEM）with energy dispersive spectroscopy（EDS）,electron probe micro analysis（EPMA）with wavelength dispersive spectrometer（WDS）,X-ray diffraction（XRD）and differential scanning calorimetry（DSC）.The results confirmed the Al₃Er phase existed with the Al₃Ho-type structure stable.It was formed through the peritectic reaction L+Al₂Er（?）Al₃Er at 1105.3±2.4 ^oC.While the Al₁₇Er₂ phase was proved to be metastable in the present work.A comprehensive thermodynamic optimization of the Al-Er binary system has been carried out by utilizing the current experimental data as well as all available results in the previous publications.A set of self-consistent thermodynamic parameters for the Al-Er/system was established.The calculated phase diagram and thermodynamic properties agree well with the available data.The artificial inverted liquid-liquid miscibility gap at high temperature in the previous evaluation is removed.The phase realation of Al rich region in Al-Ti-Er system was studied through thermodymic calculation and experiment,the experimental phase diagram of the isothermal section in the Al-rich region at 500 ^oC and liquid phase projection were obtained.There are five three-phase regions in the 500^oC isothermal section of the Al-Ti-Er system,which are（Al）+Al₃Er+τ₁,（Al）+ε（rt）-Ti Al₃+τ₂,（Al）+ε（rt）-Ti Al₃+τ₂,ε（rt）-Ti Al₃+τ₂+τ₁ andε（rt）-Ti Al₃+Al₃Er+τ₁;There are eight primary phase regions in liquid phase projection of the Al-rich region,which are（Al）,τ₁,τ₂,Al₃Er,Al₂Er,ε（ht）-Ti Al₃,ζ-Ti_2+xAl_5-xandg-Ti Al.On the basis of the experimental phase diagram data,the Al-Ti-Er system has been optimized.The Al-rich region of Al-Ti-1 wt.%B-Er phase relationship was studied through thermodynamic calculations and experiments.There are eight four-phase regions in the 500 ^oC isothermal section of the Al-rich region:Al B₁₄Er+（Al）+Ti B₂+Al B₂,Al B₄Er+B₁₂Er+（Al）+Ti B₂,Al B₄Er+Al₃Er+（Al）+Ti B₂,Al₃Er+t₁+（Al）+Ti B₂,e（rt）-Ti Al₃+t₂+（Al）+Ti B₂,t₁+t₂+e（rt）-Ti Al₃+Ti B₂,t₁+t₂+Ti B₂+（Al）,e（rt）-Ti Al₃+t₁+Al₃Er+Ti B₂.The calculated phase diagram is consistent with the experimental data.Adding rare earth Er and Al-Ti-B master alloys to 6111 aluminum alloy,the effects of grain refinement were compared,the existence mode of rare earth Er and its influence on secondary phase and mechanism were investigated.The effects of master alloys on hardness,tensile properties,and fracture morphology were analyzed.The results showed that the addition of rare earth Er and Al-Ti-B master alloys refined the grains and improved the mechanical properties.