Research On Preparation And Properties Of 6X82Al Matrix Composites Reinforced By Rare Earth And In Situ （ZrB₂+TiB₂） Particles Synthesized Under Ultrasonic Electromagnetic Coupled Field

In recent years,with the rapid development of automotive industry,environmental and energy issues become increasingly prominent,lightweight has become the focus of research in the field of automotive manufacturing.6X82 Al is a new kind of wrought aluminum alloy with medium high strength,has advantages of good plastic formability,forgeability and corrosion resistance,which has been widely used in automotive structural parts such as control arm,rear suspension and bumper,replaces the original steel structural parts gradually,and the lightweight effect is remarkable.However,with the development of technology,the demand of new high performance,energy saving automobile manufacturing for performance of materials has become increasingly strict,6X82 Al cannot satisfy the needs of high specific strength,high specific modulus and anti fatigue,therefore,to further improve the mechanical properties of 6X82 Al alloy becomes more and more important.This paper innovatively introduces rare earth Er,Y based on the existing research,with the synergistic effect of rare earth and in situ particles ZrB₂ and TiB₂,prepared 6X82 Al matrix composites enhanced by Er,Y and（ZrB₂+TiB₂）with in situ reaction synthesis technology and rare earth refinement and strengthening technology combined under ultrasonic electromagnetic coupled field,the microstructure and mechanical properties have been studied.The effects of Er,Y and（ZrB₂+TiB₂）on microstructure of 6X82 Al has been studied individually in order to get 6X82 Al composites with high performance strengthen synergistically by rare earth and in situ particles,and analyzed the characteristics of different reinforcement to determine the best content of the additives through OM,SEM,TEM,XRD,microhardness tester and other equipment.The results show that,Al3 Er,Er5Si3 precipitates formed in the solidification structure by the addition of Er,Al3 Y,Y5Si3,AlCuY precipitates formed by the addition of Y,and analyzed the characteristics of the iMPacts on other elements in the matrix alloy coMParatively,which has been found that Er is beneficial to improve the strength and ductility of the alloy and Y is more suitable for improving the ductility rather thanstrength due to the feature of Y to adsorb the Si which leads to the reduction in quantity of Mg2 Si phase as the main enhancement in the matrix.The introduction of in situ particles in 6X82 Al,there are two kinds of particles in the matrix with different size scale: the size of ZrB₂ particles with near hexagonal sharp is 80¹00nm,and TiB₂ particles with near hexagonal or quadrilateral sharp which size is 0.5¹ m;With the introduction of rare earth and in situ particles to the matrix at the same time,the number of casting defects is reduced,the reinforced particles is getting smaller and smaller,the agglomeration situation has been improved too,which promoted the comprehensive mechanical properties of the alloy.To study the changes of structure of the composites under the outside field,applied the coupled field during the preparation of the new kind of 6X82 Al composites.The results revealed that the agglomeration has been effectively suppressed,the size of particles become smaller,and the effect of the corner passivation is remarkable because of the cavitation mechanism and wave mechanism.The electromagnetic field has strong stirring effect,which leads to the regular movement of the metal melt,effectively improve the distribution of the reinforcing particles and reduce the particle size.The characteristics of ultrasonic field and electromagnetic field were studied individually,which determined the optimum parameters of coupled field: ultrasonic power is 1.5kW,the application time is 3min,the electromagnetic field current is 200 A,the frequency is 5Hz.Under the comprehensive effects of coupled,the problem of agglomeration in composites has been solved effectively,the size of particles decreased to 30⁵0nm,the corners are rounded,the particle clusters basically disappeared,and the distribution is uniform,the comprehensive mechanical properties have been improved significantly.The results of mechanical properties of alloys at room temperature showed that the tensile strength of 6X82 Al is 290 MPa,the elongation is 6.3%.The best addition of Er is 0.5wt.%,tensile strength is 325 MPa,elongation is 10.8%,coMPared to the matrix,the tensile strength and elongation increased by 12.1% and 71.4%respectively.The best addition of Y is 0.3wt.%,tensile strength is 305 MPa,elongation is 14.6%,the elongation increased by 131.7% coMPared to the matrix but theimprovement of strength is not good as Er,which revealed that Y is better used to improve the plasticity of alloy.The composites have the best mechanical properties when the content of（ZrB₂+TiB₂）is 3wt.% whose tensile strength is 322 MPa and elongation is 8.6%.According to the principle of rare earth can’t be joined too much,set the sum addition of Er and Y is 0.5wt.%,the proportion of Er and Y is 3:2,the content of（ZrB₂+TiB₂）is 3wt.%,the tensile strength and elongation of 6X82 Al composites strengthen synergistically by Er,Y and in situ particles（ZrB₂+TiB₂）is334MPa and 12.4% respectively which is higher when fabricated under the coupled field: the tensile strength is 363 MPa and elongation is 15.4%.