Abstract:A novel in-situ reaction system Al-Zr-O was developed. In-situ Al₃Zr and Al₂O₃ particulates reinforced aluminum matrix composites were fabricated by the direct melt reaction technique in the Al-Zr-O system. Microstructures of the composites and crystal morphology of in-situ formed Al₃Zr and Al₂O₃ particulates were analyzed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Results indicate that in-situ formed Al₃Zr and Al₂O₃ particles are finer and well distributed in aluminum matrix. Al₃Zr particulates with a tetragonal structure are mainly in the shape of polyhedron. A few of them are in the form of rectangle. The length/width ratio of the rectangular Al₃Zr is less than 2.0 and the maximum size is 2μm. In addition, a certain number of Al₂O₃ submicro particles with a hexagonal structure are also generated in this system. Furthermore, it is found that Al3Zr crystal grows by the mechanism of twinning. The twin plane is (11 4). The twinning direction is ［221］.The tensile tests show that the composites synthesized in the Al-Zr-O system exhibits high strength and ductility. There are a lot of ripples with fine particles on the fracture. The principal strengthening mechanisms for (Al₃Zr+Al₂O₃)_p/Al composites may include Orowan strengthening, grain-refining strengthening, solid-solution strengthening and dislocation strengthening.

Key words: in-situ synthesis; composites; Al-Zr-O; reinforcements