【摘要】 采用电磁场调控技术和直接熔体反应技术成功制备出原位纳米ZrB2 np/AA6111复合材料,研究了电磁场对复合材料微观组织的影响,分析了磁场的调控机制和微观组织对拉伸性能的影响规律。结果表明,施加电磁场可分散颗粒团聚体、改善团聚体分布、细化纳米增强颗粒(50～100 nm)并使颗粒边角变圆润,基体与颗粒的界面结合良好,干净无杂质,位错与颗粒相互交缠且密度增加。当电磁频率为10 Hz时,其最佳抗拉强度为362 MPa,屈服强度为253 MPa,伸长率为25%,分别比未施加磁场的ZrB2 np/AA6111复合材料提高了38.7%、68.6%和28.7%。更多还原

【Abstract】 6xxx alloys have become of particular interest in automotive structural applications as replacements for low carbon steels, mainly because of the increasing demand for the utilization of lighter materials in the automotive industry. However, the strength and formability of the 6xxx alloy are inferior to those of fully annealed low carbon steels, which is partially due to the different crystallographic textures of these two materials. In-situ nanoparticle-reinforced composites have always been extensively used due to their high modulus, high strength, specific stiffness and excellent comprehensive properties. However, traditional in-situ methods require long reaction time and high reaction temperatures, leading to further growth or agglomeration of the reinforcement particles and decreasing the mechanical properties. In this work, in-situ ZrB2/AA6111 composites were successfully prepared via an in-situ melt reaction with the assistance of an electromagnetic field. The effect of electromagnetic field on distribution, size and morphology of in-situ particles, interface structure between particles and matrix, and dislocation morphology in composites were characterized by XRD, OM, SEM and TEM. The action mechanism of electromagnetic field and the effect of microstructure on tensile strength were analyzed. The results indicated that with the assistance of electromagnetic field during in-situ reaction, the large particle clusters were broken into smaller clusters that were uniformly distributed in the matrix, the distribution of ZrB2 nanoparticles was diffused and homogeneous with the size decreasing to 50～100 nm, and the corners of the nanoparticlesclearly became obtuse. In addition, the interface between the particles and the matrix was well bonded without any impurities. The uniformity of the ZrB2 nanoparticle distribution improved, resulting in dislocation propagation and entanglement. When electromagnetic frequency was 10 Hz, the optimal ultimate tensile strength(UTS), yield strength(YS) and elongation(El) of the composites prepared under the electromagnetic field were 362 MPa, 253 MPa and 25%, respectively, correspondingly increasing 38.7%, 68.6%and 28.7% over the respective properties of the ZrB2 np/AA6111 composite. These improvements were due to the Orowan strengthening, load transmitting strengthening, grain refinement strengthening, and dislocation strengthening caused by the nano-sized ZrB2 particles synthesized under the coupled electromagnetic and ultrasonic field. In addition, the Orowan strengthening contributed most to the improvement of properties.更多还原