Research On Aluminum Matrix Composites Synthesized By Direct Melt Reaction Under High Intensity Ultrasonic

Aluminum matrix composites reinforced by Al₃Zr and Al₂O₃ particles have been synthesized successfully by direct melt reaction method under high intensity ultrasonic from A356-Zr(CO₃)₂, A356-K₂ZrF₆ and Al-Zr(CO₃)₂ systems, respectively. With the helps of modern analysis methods, such as SEM, XRD, EPMA and so on, the phase compositions, microstructures, mechanical properties of the composites and morphologies, distributions of the in-situ particles in matrix are investigated, and the dynamics and the mechanism of in-situ ultrasonic chemistry reactions are discussed.The results indicate that the in situ chemical reactions for A356-Zr(CO₃)₂ and A356-K₂ZrF₆ systems are speeded with the high-energy ultrasonic field introduced into the aluminum melt, volume fraction is improved, and the reaction time reduced. The in situ particles are uniformly distributed in the aluminum matrix without machine whisking. The microstructures of the composites are optimized, the grains are refined, the Si phase is grain shape, and the mechanical properties increased. The applications of the composites in industry are promoted. These are due to the cavitation effects, acoustic-streaming effects, mechanical effects and the thermal effects of the high-energy ultrasonic field. In addition, the effects of the degassing and deslagging of the ultrasonic in the melt are contributed to the properties of the composites.The results of the XRD, SEM and EPMA analysis indicate that the particles synthesized from the A356-Zr(CO₃)₂ system with ultrasonic treated are Al₂O₃ and Al₃Zr, which are uniformly distributed in the matrix, the size is about 0.5-1.5μm. The particles synthesized from the A356-K₂ZrF₆ system treated by ultrasonic field are Al₃Zr, the size is about 1-3μm, and well distributed in the matrix. The particle and the interface are combined well. The SEM and XRD of the water-quench samples results indicate that the in-situ melt reaction mechanism for the A356-Zr(CO₃)₂ system with ultrasonic assistance is reaction-cracking-diffusion.The mechanical properties test results show that the tensile strength and the elongation of the as-prepared composites are obviously increased with the increase of ultrasonic power. For the A356-Zr(CO₃)₂ system, when ultrasonic power is 1.2kW, the tensile intensity of composites is higher by nearly 14.94% than that of without treatment, reached 402.31MPa. For the A356-K₂ZrF₆ system, the tensile intensity is reached 397.6MPa. The results of the analysis of the tensile fracture morphology indicate that the tensile fracture form is visible dimple fracture character. The strength mechanisms of the as-prepared aluminum matrix composites are Orowan strength, fine-grained strength, solution strength and dislocation strength.