Abstract:A novel in-situ reaction system Al-Zr-O was developed. In situ Al₃Zr and Al₂O₃ particulate reinforced A356 alloy matrix composites have been fabricated by direct melt reaction method. The results show that the maximum sizes of Al₃Zr and Al2O₃ particulates synthesized in the system ZrOCl₂-A356 are 1μm and 3μm respectively, and they are well distributed in the matrix. The investigation shows that the Al₃Zr crystal is in the shape of polyhedron and rectangle. There is a faceted growth phenomenon on Al₃Zr crystal surface. It is firstly found that the Al₃Zr crystal grows in the mechanism of twinning. The twinning plane is (11^-4), and the twinning direction is［22^-1］. The crystal morphology of in-situ α-Al₂O₃ particulate is rectangle or sphere. Furthermore, (Al₃Zr+Al₂O₃)_p/A356 composites have not only higher tensile strength at room temperature (376.2MPa) but also higher yield strength(319.4MPa)and higher tensile strength at elevated temperature (200℃) than those of the A356 alloy. The dry sliding wear test shows that the wear resistance of the (Al₃Zr+Al₂O₃)_p/A356 composites is greatly enhanced with increasing particulate volume fraction.

Key words: in-situ synthesis; direct melt reaction; Al-Zr-O reaction system