Research On Thixoforming Of 2024 Aluminum Matrix Composites Reinforced With Nano-sized Al₂O₃ Particles

Particle reinforced aluminum matrix composites have many advantages,such as lower density,higher strength,wear resistance and thermal conductivity.Therefore,they are materials that meet the needs of the current industrial development.Aluminum matrix composites reinforced by nano size particles not only have higher strength,hardness and wear resistance,but also improve their plasticity.It is easy to prepare the components with excellent mechanical properties,high yield and complex structure by semi-solid thixotropic forming technology.In this work,the aluminum alloy matrix composites reinforced by nano particles were prepared by ultrasonic assisted semi-solid stirring.Then,the forming parts are tested and analyzed to explore the influence of process parameters on their properties,and to explore the way for large-scale fabrication of high-performance nano Al₂O₃ particles reinforced aluminum matrix composite structures.Ultrasonic assisted mechanical stirring combined with semi-solid rheological technology was used to prepare Semi-solid Billets of nano Al₂O₃ particles reinforced aluminum matrix composites.It is found that the grains in the Semi-solid Billets are almost free of deformation,and almost no dendrite exists in the microstructure,and the grains are obviously globular or rose like.The computer simulation of the process of semi-solid thixotropic forming of composite material shows that increasing the two heating temperature of the billet is beneficial to reduce the deformation resistance of the blank during forming.Increasing the loading speed and die temperature of the punch,the less heat dissipation,is beneficial to filling the mold cavity of semi-solid billet.With the increase of the two heating temperature and holding time during the thixotropic process,the liquid fraction in the material gradually increases,while the globular grains gradually increase,and some of the grains appear coalescence and growth.The content of Al in the crystal is much higher than that in the grain boundary.Mg,Cu and Fe are segregated at the grain boundary.The distribution of O element shows that the nano Al₂O₃ particles accumulate at the grain boundary,and the intragranular distribution is less than the grain boundary,and the same distribution rule is found along the extrusion direction and the vertical extrusion direction.The tensile test showed that after reinforced with nano Al₂O₃ particles,the yield strength of the matrix material changed from 150 MPa to 158 MPa,increased by 5.3%;the tensile strength changes from 273 MPa to 294 MPa,increased by 7.7%;the elongation rate changes from 3% to 5%,increased by 66.7%.According to the fracture analysis,the fracture mode of the composite material is mainly cleavage fracture,containing a small amount of ductile fracture.On forming tensile specimens for T4 heat treatment,solve the segregation of the Mg and Fe elements,reduce Cu segregation phenomenon,basically no influence on the distribution of nano Al₂O₃ particles;the best tensile strength reach 394 MPa,elongation is 5.2%.The wear resistance tests show that the wear resistance of the composites is improved by the increase of nano Al₂O₃ particles.