【作者】 许可；

【导师】 赵玉涛；

【作者基本信息】 江苏大学 ， 材料加工工程， 2007， 硕士

【摘要】 本文开发A356-Zr（CO₃）₂、A356-K₂ZrF₆及ml-ZrSiO₄反应体系，采用熔体原位反应法成功地制备了（Al₂O₃+Al₃Zr）p／A356、Al₃Zr／A356及（Al₂O₃+Al₃Zr）p／Al复合材料。研究了所制备的复合材料的相组成、凝固组织及力学性能；同时研究了原位铝基复合材料凝固组织的优化方法，并分析了不同优化工艺对原位铝基复合材料微观组织及力学性能的影响规律。X射线衍射仪（XRD）、扫描电镜（SEM）、电子探针（EPMA）分析表明：A356-Zr（CO₃）₂体系原位生成的增强颗粒为Al₂O₃和Al3_Zr，颗粒尺寸在3～4μm，且弥散分布于A356基体中；A356-K₂ZrF₆体系原位生成的增强颗粒为Al₃Zr，颗粒大小为5～7μm，同时颗粒与界面结合良好；Al-ZrSiO₄体系原位生成的增强颗粒为Al₂O₃和Al₃Zr，颗粒尺寸在2～4μm，颗粒均匀分布于基体中。不同凝固组织优化工艺对原位铝基复合材料凝固组织的影响的研究表明，对Al-ZrSiO₄体系原位合成复合材料熔体施加脉冲磁场，使得原位合成的增强颗粒比未施加磁场时变得细小，且更均匀分布于基体中。同时，随着脉冲磁场强度的增大，原位合成的增强颗粒更加细小，分布的更均匀。脉冲磁场作用时间对增强相的颗粒体积分数和大小有很大影响，最佳作用时间为15～20min。对A356-Zr（CO₃）₂体系原位合成复合材料熔体进行微量Sr变质处理，使得原位复合材料中的增强颗粒更细小，且均匀分布在基体中，同时微量Sr的加入使基体A356的Si相形貌，由粗针状变为细小的颗粒状，同时使得Al₃Zr、Al₂O₃颗粒均匀分布在基体中。对A356-K₂ZrF₆体系原位合成复合材料熔体进行快速凝固，使得Al₃Zr颗粒尺寸减小至2-4μm，且颗粒易于被凝固前沿的枝晶所捕获，分布更均匀，同时高的冷却速率使复合材料基体A356合金的共晶组织细化。对A356-Zr（CO₃）₂体系生成的复合材料进行不同温度及不同次数的重熔，结果表明，随着重熔温度的提高，重熔组织中内生颗粒的分布更均匀，形态趋于圆钝化，但过高温度的重熔导致了局部颗粒的粗化，最佳的重熔温度为850℃。随着重熔次数的增加，凝固组织中的颗粒分布更均匀，颗粒的尺寸更细小，颗粒的形态更圆整，但当重熔次数过多时，颗粒体积分数出现明显减少，因此选择5次重熔为最佳的重熔次数。对A356-Zr（CO₃）₂体系制备复合材料熔体进行高能超声处理，使得原位增强颗粒的尺寸小于2μm，且均匀分布在A356基体中。同时高能超声使得复合材料的基体A356合金中共晶Si显著细化，呈颗粒状。复合材料的力学性能研究表明，脉冲磁场作用下，Al-ZrSiO₄体系原位合成的（Al₂O₃+Al₃Zr）_p／Al复合材料的抗拉强度随着脉冲磁场强度的增大而升高，同时抗拉强度在脉冲磁场作用时间适中时达到最大值。微量Sr的变质处理，使得A356-Zr（CO₃）₂体系原位合成的（Al₂O₃+Al₃Zr）_p／A356复合材料的抗拉强度提高了14％。单辊旋淬快速凝固使得A356-K₂ZrF₆体系原位合成Al₃Zr／A356复合材料的平均显微硬度比常态下凝固的复合材料提高了22％。A356-Zr（CO₃）₂体系原位生成的（Al₂O₃+Al₃Zr）_p／A356复合材料的抗拉强度随着重熔温度的提高以及重熔次数的增加而增大，但过高温度以及过多次数的重熔导致了复合材料抗拉强度的下降。A356-Zr（CO₃）₂体系原位反应生成的（Al₃Zr+Al₂O₃）_p／A356复合材料熔体经过高能超声处理后抗拉强度比未加高能超声处理的复合材料提高了近20％。更多还原

【Abstract】 (Al₂O₃+Al₃Zr)p/A356、Al₃Zr/A356 and （Al₂O₃+Al₃Zr）p/Al composites have been successfully synthesized by direct melt reaction method from the system of A356-Zr（CO₃）₂、A356-K₂ZrF₆ and Al-ZrSiO₄ respectively. The phase composition、microstructure and mechanical properties are investigated. The ways for optimizing the microstructures of the in-situ aluminum matrix composites are studied. In additional, the effects of the variation optimization process on the microstructure and mechanical properties are investigated.The results of the XRD、SEM and EPMA analysis indicate that the particles synthesized from the A356-Zr（CO₃）₂ system are Al₂O₃ and Al₃Zr, and distributed in the matrix uniformly, the size is about 3～4μm. The particles synthesized from the A356-K₂ZrF₆ system are Al₃Zr, the size is about 5～7μm, and well distributed in the matrix. The particles synthesized from the Al-ZrSiO₄ are Al₂O₃ and Al₃Zr, the size is about 2～4μm, and distributed in the Al matrix uniformly.It is found by studying the effects of various optimization process on the microstructure that the microstructure of the as-prepared composites synthesized from the system of Al-ZrSiO₄ under pulsed magnetic field are finer, and the reinforcement particles well distributed in the Al matrix than under zero magnetic field. With the plused magnetic intensity increasing, the sizes and distributions of in-situ particles in the matrix become refiner and more homogenous. The volume fraction and the size of the reinforcement particles are obviously affected by the applying time of the pulsed magnetic field into the aluminum melt, the best time is 15～20min. The in-situ particles synthesized from the system of A356-Zr（CO3）₂ are uniformly distributed in the matrix by strontium modification treatment, the size is less than 3μm, and the particles have not been rejected by the solid/liquid interface, but captured in the solid. The morphologies of Si in the A356 matrix are changed from coarse needle-shape to fine grain-shape. The results of the effects for the rapid solidification on the microstructure of the composites synthesized from the A356-K₂ZrF₆ system indicate that the particles become refiner and easier to be captured by the dendritics in the rim of the solidification. In additional, the eutectic structure of A356 matrix are refined by the excessive cooling rate. The composites synthesized from the system of A356-Zr（CO₃）₂ are remelted at different temperatures. The sizes and distributions of in-situ particles become refiner and more uniformly with increasing the remelting temperature. But the excessive high temperature results in the coarsening of in-situ particles, the optimal remelting temperature is 850℃. With the increase of the remlting frequency, the in-situ particles become refiner and well distributed. But the excessive remelting frequency lead to the decrease of particles volume fraction. The optimal remelting times is five. The sizes of the in-situ Al₂O₃ and Al₃Zr particles synthesized from the system of A356-Zr（CO₃）₂ by in-situ reaction assisting with high-intensity ultrasonic are less than 2μm, and the particles well distributed in the A356 matrix. The morphologies of Si in the A356 matrix are changed from coarse needle-shape to fine grain-shape.The results of the mechanical property testing of the composites show that the ultimate tensile strength of （Al₂O₃+Al₃Zr）_p/Al composites synthesized from the Al-ZrSiO₄ system are increased with increasing the plused magnetic intensity, and the max. value of the tensile strength can be obtained with the suitable applying time for the pulsed magnetic field. The tensile strength of the composites synthesized by A356-Zr（CO₃）₂ with strontium modification treatment is 14％higher than that of without treatment. Rapid solidification makes the micro-hardness of Al₃Zr/A356 composites prepared by A356-K₂ZrF₆ higher by 22％than that without. The tensile strength of the composites prepared by the A356-Zr（CO₃）₂ become higher with the increasing of the remelting temperature and remelting times, and decease with excessive remelting temperature times. When the melt is treated with high-intensity ultrasonic during the fabrication of the composites from A356-Zr（CO₃）₂ system, the tensile strength is higher by nearly 20％than that of without treating.更多还原