| (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. |
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