Preparation and microstructure of in-situ (ZrB2+Al2O3+Al3Zr)p/A356 composite synthesized by melt direct reaction

(ZrB2+Al2O3+Al3Zr)/A356 composites were synthesized by melt direct reaction from A356-(K2ZrF6+KBF4+Na2B4O7) system. The phase compositions and the microstructures of the as-prepared composites were investigated by XRD, SEM and TEM. The results show that the reinforcements are composed of ZrB2 and Al2O3 ceramic phase particles and Al3Zr intermetallic particles. The ZrB2 particulates are easy to join together to form some particle clusters and distribute along the α(Al) grain boundary. The morphologies of the ZrB2 particulates are in hexagon-shape with the size of about 50 nm. The TEM investigation results of Al3Zr indicate that Al3Zr grows in the form of facet with the length-diameter ratio of about 20. The morphologies of Al2O3 particles are in rectangular-shape and ellipsoidal-shape, with the size of about 0.1 μm. In addition, the interfaces of the matrix and particles are net and no interfacial outgrowth is observed.