| 2024 Al matrix composites with more excellent performance can be obtained by the combination of aluminum alloy and reinforcement?Ceramic particles,metal compounds,etc.?.TiAl3 has high hardness,specific strength,wear resistance and high temperature stability,therefore it's could be used as reinforcement materials.The interface between reinforcement and matrix can be improved by introducing in-situ synthesis TiAl3 particles.The disadvantage of traditional mechanical stirring in-situ synthesis method is poor dispersion,high porosity,high content of oxide inclusions,and long rod brittle TiAl3 phase was easy to be obtained.Based on above situation,this paper proposed that particle reinforced TiAl3/2024Al composites could be prepared by assisted ultrasound.The reaction process of globular solid Ti powder and 2024 Al melt under ultrasonic vibration was studied in this paper.The result shows that,the only product obtainded from in-situ casting process is TiAl3 particles.The trend of TiAl3's growth along?001?crystal face direction caused by the electronic structure was breaked due to local high temperature and high pressure produced by high intensity ultrasonic.The reaction rate between solid Ti and Al melt is dominated by diffusion of Ti through the TiAl3 layer.The kinetic exponent n of in-situ TiAl3 in this work is determined to be 0.86,which is much higher than that of standard diffusion-controlled growth?n=0.5?.Particle reinforced TiAl3/2024Al composites were prepared by assisted ultrasound in-situ casting method.The research result shows that the changes of reaction temperature,time and TiAl3 mass fraction have a great influence on Ti-Al reaction and microstructure of composite.After ultrasonic treatment of 15min at 835?,added Ti particles were completely reacted,and TiAl3/2024Al composites without Ti particles were obtained.With the increase of time,reinforcement particles gradually grow up.With the increase of reaction temperature,reaction rate was increased,size of the ?-Al grain decreased and microstructure homogeneity is improved.However,the high temperature has a negative effect on alloy composition and performance.Matrix microstructure and morphology of TiAl3 particles are not affected by mass fraction of reinforcement.With the increase of the reaction temperature,hardness of TiAl3/2024 composites;with the increase of reaction time,hardness of TiAl3/2024 composites increased first and then decreased.With the increase of proportion,hardness of TiAl3/2024 composites increased.Yield strength and tensile strength of 8wt.%TiAl3/2024Al composites are 446MPa and 357MPa,respectively.Compared with the 2024 aluminum alloy without the introduction of TiAl3 particles,strength of the composites increased by about 30%.In this paper,reasons for the increase of the yield strength of the composites are analyzed and the theoretical verification is carried out.Friction and wear test shows that TiAl3/2024Al composite has excellent wear resistance at room temperature.At high temperature friction and wear test,with the change of experimental temperature,the change of wear rate is not regular.Wear rate is increased with the increase of TiAl3 content when the experimental temperature below 300?,while wear rate decreased at 300?.This paper argues that this phenomenon is related to the formation of Al2O3 film,blocking effect of TiAl3 particles on the formation of Al2O3 and the oxidation resistance of TiAl3.High temperature compression experiments of 8wt.%TiAl3/2024Al composite were carried out on Gleeble-3500D thermal simulation test machine.In this paper,high temperature flow stress variation law is studied,and the constitutive model which can accurately describe flow stress characteristics of the composite is established.The average relative error between predicted stress and experimental stress is 4.78%.Based on experimental data of high temperature thermal compression,the hot processing map that can provide reference for forging process is established.In this paper,die forging experiment of 8wt.%TiAl3/2024Al composite is carried out.The result shows that,TiAl3 particles greatly affect the microstructure of cup-shaped forging in high strain zone.The higher the forming temperature,the finer the microstructure uniformity of TiAl3 and grain boundary precipitates.With the increase of forming temperature,TiAl3 particles and grain boundary precipitates are finer,and the microstructure becomes uniform.With deformation densification,hardness of the composites is increased,and with the increase of forging temperature,tensile strength is slightly increased.In this paper,reaction kinetics process and control conditions of TiAl3/2024Al composite prepared by ultrasound assisted in situ casting are analyzed.The preparation process of TiAl3/2024Al composites was studied systematically.The simulation and experimental study of TiAl3/2024Al composites are carried out based on constitutive equation and hot processing map,which provide important theoretical basis for the forming of in situ composites. |
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